Comparative developmental toxicity of a comprehensive suite of polycyclic aromatic hydrocarbons

Particle size-based evaluation of stormwater control measures in reducing solids, polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs)

This study evaluates the effectiveness of various stormwater control measures (SCMs) in removing polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs), both in dissolved forms and associated with different-sized solids. The SCMs evaluated include biofilters, a hybrid biofilter + media filter, a retention pond, and treatment trains with hydrodynamic separators and cartridge filters. The targeted particle size fractions were clay (0.7-2.7 µm), fine silt (2.7-20 µm), coarse silt (20-63 µm), and sand (>63 µm), along with their associated PAHs and PCBs. Samples were collected from multiple storm events at the inlets and outlets of these SCMs on current and former military bases in the Southwestern and Northwestern US. The study found that coarse particles (>20 µm) contained significantly higher fractions of organic carbon (foc), which correlated with higher concentrations of contaminants in these particulates. All SCMs effectively reduced particulate-bound contaminants, especially within the coarse particle fractions, but the removal of aqueous phase contaminants was generally minimal. Despite the overall effectiveness of the SCMs, maintenance challenges-such as biofilter erosion and insufficient cleanout of cartridge filters-can hinder their performance. The study highlights the importance of considering particle size and its relationship to contaminant distribution to comprehensively assess the performance of stormwater control measures and the potential for sediment recontamination.

Knockdown of cytochrome P450 1 A (cyp1a) gene suppresses growth and oxygen tolerance in zebrafish

Cyp1a (cytochrome P450 1 A) is critical for metabolizing endogenous substances and environmental chemicals. In this study, a zebrafish strain KI (cyp1a:mcherry), exhibiting low cyp1a gene expression, was compared with wild-type zebrafish (WT) to investigate the effects of cyp1a on growth and hypoxia tolerance. The results demonstrated that low cyp1a expression significantly inhibited zebrafish growth and reduced hypoxia tolerance. Specifically, KI zebrafish exhibited slower growth rates and higher sensitivity to low oxygen conditions compared to WT. These physiological phenotypes directly link low cyp1a expression to impaired growth and reduced environmental adaptation. Transcriptomic analysis revealed potential mechanisms underlying these effects, including up-regulation of digestive system-related genes (e.g., cpa1, cpb1) and dysregulation of pathways involved in detoxification, stress response, and steroid biosynthesis. These findings highlight the importance of maintaining normal cyp1a expression for healthy growth and environmental adaptation in zebrafish.

Toxicity mechanisms of polycyclic aromatic hydrocarbons to Manila clam Ruditapes philippinarum: oxidative stress and oxidative damage

Polycyclic Aromatic Hydrocarbons (PAHs) are bioaccumulative and highly toxic, posing a significant threat to the security of marine ecosystems. Bivalves are still one of the marine invertebrates with high species diversity despite experiencing environmental pollution. In this paper, we focused on the detoxification metabolism and toxicological impacts of a representative mixture of PAHs (Phenanthrene: Chrysene: Benzo(a)pyrene = 1:1:1) on Ruditapes philippinarum. Our observations confirm that PAHs exhibited strong bioaccumulation and induced detoxification processes, as evidenced by the up-regulation of detoxification enzymes and genes in Phase I and Phase II reactions. Additionally, the results regarding the toxic effects of PAHs, such as the inhibition of DNA repair and damage to biomacromolecules and tissues, suggested that DNA damage, lipid peroxidation, and protein glycosylation may serve as potential biomarkers for PAHs contamination. However, the transition from induction to suppression in the antioxidant defense system revealed a more sophisticated strategy in clams to balance detoxification and antioxidant demands. Therefore, given the potential influence of other stressors, further validation under field conditions is necessary. This research contributes to a deep understanding of the toxic responses of marine invertebrates to PAHs stress and provides a more comprehensive basis for monitoring PAHs pollution in marine environments.

Transcriptomics uncover inhibition of repair and wound healing pathways in Atlantic halibut (Hippoglossus hippoglossus) after crude oil exposure

Accidental oil spills significantly threaten marine ecosystems and fisheries, impacting biodiversity and ecological health. This study examines the downstream transcriptomic responses of Atlantic halibut larvae exposed to crude oil during organogenesis. Findings show concentration-dependent transcriptional abnormalities. Pathway analysis at 10 days post-hatch (dph), 11 days after cessation of oil exposure, indicates downregulation of inflammatory and reparative pathways. By 18 dph, tissue-specific analyses reveal activation of these pathways, especially in head tissues, alongside upregulation of neuronal signaling pathways. This highlights the complex relationship between oil exposure and transcriptional responses, emphasizing recovery mechanisms represented by regulation of inflammatory, repair and wound healing pathways following oil exposure. The activation of repair pathways in surviving larvae suggests compensatory processes to address oil-induced damage. These novel insights enhance understanding of the molecular mechanisms of oil toxicity and the lasting effects on marine organisms.

Profiling aerosol Polycyclic Aromatic Compounds (PACs) in a severely polluted European city: A comprehensive assessment of the residential biomass burning impact on atmospheric toxicity

Fine aerosol Polycyclic Aromatic Hydrocarbons (PAHs), Oxygenated Polycyclic Aromatic Hydrocarbons (OPAHs) and other PM2.5 components were quantified in Ioannina, a Southeastern European city facing severe air quality degradation due to residential biomass burning (BB). Polycyclic Aromatic Compound (PAC) seasonal means were extremely enhanced in winter compared to summer (by 98 and 88 times for PAHs and OPAHs, respectively). Benzo(a)pyrene (BaP) registered a 347-fold winter increase, and its estimated annual mean was 2.4 times higher than the EU standard. Medium- and high-molecular weight PAC species correlated well with PM2.5 DTTv activity (R2: 0.48 and 0.54, respectively), suggesting also their significant non-carcinogenic potential. These PAC groups were strongly associated with methanol- and water-soluble Brown Carbon absorption (R2 > 0.7). Source apportionment by Positive Matrix Factorization (PMF) on the speciation dataset indicated BB as the major aerosol source, contributing > 80 % to average Σ-PAC concentrations and their carcinogenic potential during the study period. The PAC carcinogenic risk assessment highlighted the importance of considering the inclusion of not only legacy PAHs but also emerging species with very high estimated toxicity, such as Benzo(c)fluorene and Dibenzo-pyrenes. Observed concentrations were alarming, posing substantial short- and especially long-term risks. Therefore, there is an urgent need to regulate residential BB in Ioannina and similar urban environments in SE Europe.

Identification of Potentially Toxic Transformation Products Produced in Polycyclic Aromatic Hydrocarbon Bioremediation Using Suspect and Non-Target Screening Approaches

Polycyclic aromatic hydrocarbons (PAHs) are a class of ubiquitous environmental contaminants that can be remediated through physical, chemical, or biological means. Treatment strategies can lead to the formation of PAH-transformation products (PAH-TPs) that, despite having the potential for adverse ecological and human health effects, are unregulated and understudied in environmental monitoring and remediation. Unavailability of reference standards for PAH-TPs limits the ability to identify PAH-TPs by targeted methods. This study utilized suspect and nontarget screening approaches to identify PAH-TPs produced by a bacterial culture, Rhodococcus rhodochrous ATCC 21198, using liquid chromatography-high resolution mass spectrometry. Open-source tools were used to predict biotransformation products, predict potential PAH-TP structures from mass spectra, and estimate health hazards of potential PAH-TPs. The workflow developed in this study allowed for the tentative identification of 16 PAH-TPs (confidence levels 2a to 3), seven of which were not previously detected by targeted analysis. Several new potential transformation pathways for our bacterial pure culture were suggested by the PAH-TPs, including carboxylation, sulfonation and up to three hydroxylation reactions. A computational toxicity assessment indicated that the PAH-TPs shared many hazard characteristics with their parent compounds, including genotoxicity and endocrine disruption, highlighting the importance of considering PAH-TPs in future PAH studies.

Transformation of polycyclic aromatic hydrocarbons during frying stinky tofu

Reductions in polycyclic aromatic hydrocarbon (PAH) concentrations have been observed during frying. However, transformation mechanisms of PAHs remain unclear. We hypothesize that PAHs may be oxidized into oxygenated polycyclic aromatic hydrocarbons (OPAHs) and other derivatives during frying. First, the levels of 24 PAHs and 12 OPAHs during frying stinky tofu were evaluated. Among the OPAHs, 9,10-anthraquinone exhibited the greatest increase in frying oil, with an increase rate of 55 %. The transformation of anthracene into 9,10-anthraquinone was further confirmed through stable isotope tracing. Targeted and untargeted mass spectrometry analyses suggested that anthrone, heavy PAHs, and alkyl derivatives were also produced from anthracene. Theoretical calculations revealed that radical addition was kinetically and thermodynamically more favourable than hydrogen abstraction in the initial reaction of anthracene. This study systematically elucidates, for the first time, the transformation mechanisms of anthracene in frying oil, paving the way for reducing health risks associated with PAHs.

High molecular weight polycyclic aromatic hydrocarbon (HMW-PAH) isomers: unveiling distinct toxic effects from cytotoxicity to oxidative stress-induced DNA damage

Polycyclic aromatic hydrocarbons (PAHs) represent one of the most extensive classes of known carcinogenic and genotoxic compounds widely distributed across the globe. Particularly relevant to ecotoxicological studies is the possible presence of PAHs with molecular weight (MW) 302 Da. Since the toxicity of 302 Da PAHs differs significantly from isomer to isomer, understanding their relative toxicity is essential for assessing their potential risks to human health. This study investigates the toxic effects of micromolar concentrations of four HMW-PAHs isomers of MW = 302 Da, namely dibenzo(b,l)fluoranthene (DB(b,l)F), dibenzo(a,j)fluoranthene (DB(a,j)F), dibenzo(a,l)fluoranthene (DB(a,l)F) and naphtho(1-2j)fluoranthene (N(1-2j)F), upon exposure and metabolic activation in HepG2 cells. Appropriate assays were selected to investigate their potential to disrupt cellular viability and to induce cytotoxicity, apoptosis/necrosis, genotoxicity, and oxidative stress with DNA damage. After 48 h of exposure time, DB(a,l)F was the only isomer to reduce cellular viability in a concentration-dependent manner. In all cases, apoptosis was the main mechanism of HepG2 cell death, which could be induced by the significant DNA damage and an increase in 8-hydroxy-2'-deoxyguanosine (8-OHdG) adduct level formation. The highest concentrations of DB(a,l)F tested exhibited the greatest potential to induce HepG2 DNA damage and 8-OHdG formation. Altogether, these facts demonstrate that the distinct arrangements of the atoms in HMW-PAHs isomers can impact on their toxic potential and that DB(a,l)F was the most toxic isomer evaluated in this study. These results shed light on the importance to thoroughly characterize MW302 PAHs to substantiate their human and environmental risk assessments.

Tracing PAH emissions from leisure boats in a low tidal coastal area, including comparison with Environmental Quality Standards (EQS)

The approximately 850,000 recreational boats in Sweden, has shown to have a significant impact on the marine environment of the Swedish west coast. The extensive weather-protected archipelagos and fjords with minor tidal activity, offers excellent conditions to uncover traces of leisure boats exhaust from the background. In this study we focus on polycyclic aromatic hydrocarbons (PAHs) from boat exhausts in surface sediments and water (using SPMD) in a busy harbour and a pristine fjord. The PAH analyses were performed using gas chromatography - mass spectrometry after suitable extraction procedures. Concentrations of total PAHs in water and sediments was 4-8 ng/L and 200-5500 ng/g respectively. In addition to PAH measurements, we used the number of documented motorboat passages together with residence time of water, to quantify the concentration enhancement of up to 40% due to recreational boating. Here we have for the first time succeeded in distinguishing the leisure boat PAH signature in coastal marine environments. This by combining our data and observed compositions from lakes where emissions from leisure boats is documented as a dominating source of pollution. Comparisons with Environmental Quality standards (EQS) showed elevated levels of up to more than five times in the most exposed sediments, while the water concentrations were below the EQS. The study concludes that boating activities significantly contribute to PAH-levels in these coastal environments, with implications for environmental management and pollution mitigation strategies.

Developmental toxicity of alkylated PAHs and substituted phenanthrenes: Structural nuances drive diverse toxicity and AHR activation

Polycyclic aromatic hydrocarbons (PAHs) are a diverse class of chemicals that occur in complex mixtures including parent and substituted PAHs. To understand the hazard posed by complex environmental PAH mixtures, we must first understand the structural drivers of activity and mode of action of individual PAHs. Understanding the toxicity of alkylated PAHs is important as they often occur in higher abundance in environmental matrices and can be more biologically active than their parent compounds. 104 alkylated PAHs were screened from 11 different parent compounds with emphasis on substituted phenanthrenes and their structurally dependent toxicity differences. Using a high-throughput early life stage zebrafish assay, embryos were exposed to concentrations between 0.1 and 100 μM and assessed for morphological and behavioral outcomes. The aryl hydrocarbon receptor (AHR) is often implicated in the toxicity of PAHs and the induction of cytochrome P4501A (cyp1a) is an excellent biomarker of Ahr activation. Embryos were evaluated for cyp1a induction using a fluorescence reporter line. Alkyl and polar phenanthrene derivatives were further assessed for spatial cyp1a expression and Ahr dependence of morphological effects. In the alkyl PAH screen 35 (33.7%) elicited a morphological or behavioral response and of those 23 (65%) also induced cyp1a. 31 (29.8%) of the chemicals only induced cyp1a. Toxicity varied substantially in response to substitution location, the amount of ring substitutions and alkyl chain length. Cyp1a induction varied by parent compound group and was a poor indicator of morphological or behavioral outcomes. Polar phenanthrenes were more biologically active than alkylated phenanthrene derivatives and their toxicity was not dependent upon the Ahr2, Ahr1a or Ahr1b when tested individually, despite cyp1a induction by 50% of polar phenanthrenes. Our results demonstrated that induction of cyp1a did not always correlate with PAH toxicity or Ahr dependence and that the type and location of phenanthrene substitution determined potency.

Cell Painting for cytotoxicity and mode-of-action analysis in primary human hepatocytes

High-throughput, human-relevant approaches for predicting chemical toxicity are urgently needed for better decision-making in human health. Here, we apply image-based profiling (the Cell Painting assay) and two cytotoxicity assays (metabolic and membrane damage readouts) to primary human hepatocytes after exposure to eight concentrations of 1085 compounds that include pharmaceuticals, pesticides, and industrial chemicals with known liver toxicity-related outcomes. Three computational methods (CellProfiler, a Cell Painting-specific convolutional neural network, and a pretrained vision transformer) were compared to extract morphology features from single cells or entire images. We used these morphology features to predict activity in the measured cytotoxicity assays, as well as in 412 curated ToxCast assays that span cytotoxicity, cell-based, and cell-free categories. We found that the morphological profiles detect compound bioactivity at lower concentrations than standard cytotoxicity assays. In supervised analyses, they predict cytotoxicity and targeted cell-based assay readouts, but not cell-free assay readouts. We also found that the various feature extraction methods performed relatively similarly and that filtering out non-bioactive or cytotoxic concentrations did not boost supervised assay prediction performance for any assay endpoint category, although it did have a large influence on unsupervised cluster analysis. We envision that image-based profiling could serve as a key component of modern safety assessment.

Rapid determination of chemical losses in a microplate bioassay using fluorescence spectroscopy

The increase in production and innovation of chemicals that humans interface with has enhanced the need for rapid toxicity testing of new and existing chemicals. This need, along with efforts to reduce animal testing, has led to the development of high-throughput bioassays typically conducted in microplates. These bioassays offer time and resource advantages over traditional animal models; however, significant chemical losses can occur in microplates. Current methods for measuring chemical losses in microplates require extensive sample preparation and highly sensitive instruments. We propose the use of fluorescence spectroscopy to measure chemical losses in high-throughput bioassays as a low resource alternative to the existing methods. A fluorescent plate reader was used to develop methods for quantifying the aqueous concentrations of two chemicals, 2-hydroxynaphthalene and acridine, in microwells of a 96-well microplate. A high-throughput, 5 day embryonic zebrafish bioassay was used as the model bioassay for method development. Chemical losses were attributed to a combination of photodegradation, sorption, and uptake by the zebrafish embryos, kinetics of which were derived from a pseudo-first order model. Chemical uptake amount was calculated to be approximately 50% and 21% of the total chemical amount added for 2-hydroxynaphthalene and acridine, respectively. Unexpected cranial deformities were observed in the embryonic zebrafish, suggesting further investigation of potential additive toxicity of the ultraviolet radiation exposure from fluorescence measurements and chemical exposure is needed. Nonetheless, this novel method provides a rapid, low resource approach to measuring chemical losses in microplates that can be extended to a variety of autofluorescent chemicals and microplate-based bioassays.

Divergent Transport Dynamics of Alkylated versus Unsubstituted Polycyclic Aromatic Hydrocarbons at the Air-Water and Sediment-Water Interfaces at a Legacy Creosote Site

Alkylated polycyclic aromatic hydrocarbons (PAHs) are abundant constituents of many PAH mixtures and contribute to risk at contaminated sites. Despite their abundance, the movement of alkylated PAHs remains understudied relative to unsubstituted PAHs. In the present study, passive sampling devices were deployed in the air, water, and sediments at 11 locations across multiple seasons to capture spatial and temporal variability in the abundance and movement of alkylated PAHs at a Brownsfield creosote site in Oregon, USA. Freely dissolved concentrations of 18 alkyl homologous series were quantified by gas chromatography-triple quadrupole mass spectrometry. Alkylated PAHs were consistently more abundant than unsubstituted PAHs in all sampled media (sum PAH and APAH concentrations 43-96% alkyl PAHs). Models of diffusive and advective flux revealed abundant 2 and 3-ring alkyl PAHs exhibited seasonal differences in movement, particularly across the air-water interface. The novel application of these methods to freely dissolved alkylated PAH homologues revealed that, in many instances, alkylated PAHs, particularly C3 and C4 homologues, moved in the opposite direction as unsubstituted PAHs across both the air-water and sediment-water interfaces. These findings reinforce the need to characterize alkylated PAHs and seasonal variability and can inform future sampling at contaminated sites.

Adverse neurodevelopment in children associated with prenatal exposure to fine particulate matter (PM2.5) - Possible roles of polycyclic aromatic hydrocarbons (PAHs) and mechanisms involved

Prenatal exposure to ambient fine particles (PM2.5) and polycyclic aromatic hydrocarbons (PAHs) has been associated with adverse birth outcomes including neurodevelopmental effects with cognitive and/or behavioral implications in early childhood. As a background we first briefly summarize human studies on PM2.5 and PAHs associated with adverse birth outcomes and modified neurodevelopment. Next, we add more specific information from animal studies and in vitro studies and elucidate possible biological mechanisms. More specifically we focus on the potential role of PAHs attached to PM2.5 and explore whether effects of these compounds may arise from disturbance of placental function or more directly by interfering with neurodevelopmental processes in the fetal brain. Possible molecular initiating events (MIEs) include interactions with cellular receptors such as the aryl hydrocarbon receptor (AhR), beta-adrenergic receptors (βAR) and transient receptor potential (TRP)-channels resulting in altered gene expression. MIE linked to the binding of PAHs to cytochrome P450 (CYP) enzymes and formation of reactive electrophilic metabolites are likely less important. The experimental animal and in vitro studies support the epidemiological findings and suggest steps involved in mechanistic pathways explaining the associations. An overall evaluation of the doses/concentrations used in experimental studies combined with the mechanistic understanding further supports the hypothesis that prenatal PAHs exposure may cause adverse outcomes (AOs) linked to human neurodevelopment. Several MIEs will likely occur simultaneously in various cells/tissues involving several key events (KEs) which relative importance will depend on dose, time, tissue, genetics, other environmental factors, and neurodevelopmental endpoint in study.

Behavior and toxicological impact of spilled diluted bitumen and conventional heavy crude oil in the unsaturated zone

Demand for unconventional crude oils continues to drive the production of diluted bitumen (dilbit) within Western Canada, promoting increased transport volumes across the extensive 700,000 km pipeline system of Canada and the USA. Despite this vast extent of terrestrial transport, the current understanding of the behavior and fate of spilled dilbit within shallow groundwater systems is limited. To this end, oil spill experiments with a dilbit (Cold Lake Blend) and a physicochemically similar conventional heavy crude oil (Conventional Heavy Blend) were conducted for 104 days in large soil columns (1 m height × 0.6 m diameter) engineered to model contaminant transport in the unsaturated (vadose) zone. Around two-fold greater concentrations and 6-41 % faster rates of vadose zone transport of benzene, toluene, ethylbenzene and xylenes (BTEX) and polycyclic aromatic compounds (PACs) were observed in the dilbit- compared to conventional heavy crude-contaminated columns. As determined by Orbitrap mass spectrometry, the OxSx species abundances in the acid extractable organics (AEOs) fraction of column leachate from both oil types increased over time, ostensibly due to microbial degradation of petroleum. Bioaccumulation of petroleum constituents in fathead minnow (Pimephales promelas) larvae exposed to contaminated leachate was confirmed through the induction of developmental malformations lasting up to 34 days and increased abundance of cyp1a mRNA observed throughout the experiment. Toxicity was comparable between the two oils but could not be fully attributed to metals, BTEX, PACs or AEOs, implying the presence of uncharacterized teratogens capable of being transported within the vadose zone following terrestrial dilbit and conventional heavy crude oil surface spills.

Aryl hydrocarbon receptor-dependent toxicity by retene requires metabolic competence

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds frequently detected in the environment with widely varying toxicities. Many PAHs activate the aryl hydrocarbon receptor (AHR), inducing the expression of a battery of genes, including xenobiotic metabolizing enzymes like cytochrome P450s (CYPs); however, not all PAHs act via this mechanism. We screened several parent and substituted PAHs in in vitro AHR activation assays to classify their unique activity. Retene (1-methyl-7-isopropylphenanthrene) displays Ahr2-dependent teratogenicity in zebrafish, but did not activate human AHR or zebrafish Ahr2, suggesting a retene metabolite activates Ahr2 in zebrafish to induce developmental toxicity. To investigate the role of metabolism in retene toxicity, studies were performed to determine the functional role of cyp1a, cyp1b1, and the microbiome in retene toxicity, identify the zebrafish window of susceptibility, and measure retene uptake, loss, and metabolite formation in vivo. Cyp1a-null fish were generated using CRISPR-Cas9. Cyp1a-null fish showed increased sensitivity to retene toxicity, whereas Cyp1b1-null fish were less susceptible, and microbiome elimination had no significant effect. Zebrafish required exposure to retene between 24 and 48 hours post fertilization (hpf) to exhibit toxicity. After static exposure, retene concentrations in zebrafish embryos increased until 24 hpf, peaked between 24 and 36 hpf, and decreased rapidly thereafter. We detected retene metabolites at 36 and 48 hpf, indicating metabolic onset preceding toxicity. This study highlights the value of combining molecular and systems biology approaches with mechanistic and predictive toxicology to interrogate the role of biotransformation in AHR-dependent toxicity.

Environmental significance of PAH photoproduct formation: TiO2 nanoparticle influence, altered bioavailability, and potential photochemical mechanisms

Interactions between polycyclic aromatic hydrocarbons (PAHs) and titanium dioxide (TiO2) nanoparticles (NPs) can produce unforeseen photoproducts in the aqueous phase. Both PAHs and TiO2-NPs are well-studied and highly persistent environmental pollutants, but the consequences of PAH-TiO2-NP interactions are rarely explored. We investigated PAH photoproduct formation over time for benzo[a]pyrene (BaP), fluoranthene (FLT), and pyrene (PYR) in the presence of ultraviolet A (UVA) using a combination of analytical and computational methods including, identification of PAH photoproducts, assessment of expression profiles for gene indicators of PAH metabolism, and computational evaluation of the reaction mechanisms through which certain photoproducts might be formed. Chemical analyses identified diverse photoproducts, but all PAHs shared a primary photoproduct, 9,10-phenanthraquinone (9,10-PQ), regardless of TiO2-NP presence. The computed reaction mechanisms revealed the roles photodissociation and singlet oxygen chemistry likely play in PAH mediated photochemical processes that result in the congruent production of 9,10-PQ within this study. Our investigation of PAH photoproduct formation has provided substantial evidence of the many, diverse and congruent, photoproducts formed from physicochemically distinct PAHs and how TiO2-NPs influence bioavailability and time-related formation of PAH photoproducts.

Evaluation of historical data on persistent organic pollutants and heavy metals in Lake Baikal: Implications for accumulation in marine environments

Lake Baikal, the largest freshwater lake by volume, provides drinking water and aquatic food supplies to over 2.5 million people. However, the lake has been contaminated with recalcitrant pollutants released from surrounding industrial complexes, agriculture, and natural lands, thereby increasing the risk of their bioaccumulation in fish and seals. Yet, a collective analysis of historical concentration data and their bioaccumulation potential as well as what factors drive their accumulation in fish or seals remains largely unknown. We analyzed concentration data from 42 studies collected between 1985 and 2019 in water, sediment, fish, and seals of Lake Baikal. Heavy metals had the highest concentrations in water and biota followed closely by polycyclic aromatic hydrocarbons (PAHs) and organochlorines. Among organochlorines, polychlorinated biphenyls (PCBs) showed the highest levels in water, surpassing hexachlorocyclohexane (HCH) concentrations, particularly after normalizing to solubility. While naphthalene and phenanthrene exhibited the highest average concentrations among polycyclic aromatic hydrocarbons (PAHs), their relative concentrations significantly decreased upon solubility normalization. The analysis confirmed that bioconcentration and biomagnification of organochlorine pesticides, PCBs, PAHs, and heavy metals depend primarily on source strength to drive their concentration in water and secondarily on their chemical characteristics as evidenced by the higher concentrations of low-solubility PCBs and high molecular weight PAHs in water and sediment. The differential biomagnification patterns of Cu, Hg, and Zn compared to Pb are attributed to their distinct sources and bioavailability, with Cu, Hg, and Zn showing more pronounced biomagnification due to prolonged industrial release, in contrast to the declining Pb levels. Dibenzo-p-dioxins were detected in sediment and seals, but not in water or fish compartments. These data highlight the importance of addressing even low concentrations of organic and inorganic pollutants and the need for more consistent and frequent monitoring to ensure the future usability of this and other similar essential natural resources.

Activity-Based Protein Profiling to Probe Relationships between Cytochrome P450 Enzymes and Early-Age Metabolism of Two Polycyclic Aromatic Hydrocarbons (PAHs): Phenanthrene and Retene

A growing body of literature has linked early-life exposures to polycyclic aromatic hydrocarbons (PAH) with adverse neurodevelopmental effects. Once in the body, metabolism serves as a powerful mediator of PAH toxicity by bioactivating and detoxifying PAH metabolites. Since enzyme expression and activity vary considerably throughout human development, we evaluated infant metabolism of PAHs as a potential contributing factor to PAH susceptibility. We measured and compared rates of phenanthrene and retene (two primary PAH constituents of woodsmoke) metabolism in human hepatic microsomes from individuals ≤21 months of age to a pooled sample (n = 200) consisting primarily of adults. We used activity-based protein profiling (ABPP) to characterize cytochrome P450 enzymes (CYPs) in the same hepatic microsome samples. Once incubated in microsomes, phenanthrene demonstrated rapid depletion. Best-fit models for phenanthrene metabolism demonstrated either 1 or 2 phases, depending on the sample, indicating that multiple enzymes could metabolize phenanthrene. We observed no statistically significant differences in phenanthrene metabolism as a function of age, although samples from the youngest individuals had the slowest phenanthrene metabolism rates. We observed slower rates of retene metabolism compared with phenanthrene also in multiple phases. Rates of retene metabolism increased in an age-dependent manner until adult (pooled) metabolism rates were achieved at ∼12 months. ABPP identified 28 unique CYPs among all samples, and we observed lower amounts of active CYPs in individuals ≤21 months of age compared to the pooled sample. Phenanthrene metabolism correlated to CYPs 1A1, 1A2, 2C8, 4A22, 3A4, and 3A43 and retene metabolism correlated to CYPs 1A1, 1A2, and 2C8 measured by ABPP and vendor-supplied substrate marker activities. These results will aid efforts to determine human health risk and susceptibility to PAHs exposure during early life.

PAH bioremediation with Rhodococcus rhodochrous ATCC 21198: Impact of cell immobilization and surfactant use on PAH treatment and post-remediation toxicity

Polycyclic aromatic hydrocarbons (PAHs) are prevalent environmental contaminants that are harmful to ecological and human health. Bioremediation is a promising technique for remediating PAHs in the environment, however bioremediation often results in the accumulation of toxic PAH metabolites. The objectives of this research were to demonstrate the cometabolic treatment of a mixture of PAHs by a pure bacterial culture, Rhodococcus rhodochrous ATCC 21198, and investigate PAH metabolites and toxicity. Additionally, the surfactant Tween ® 80 and cell immobilization techniques were used to enhance bioremediation. Total PAH removal ranged from 70-95% for fluorene, 44-89% for phenanthrene, 86-97% for anthracene, and 6.5-78% for pyrene. Maximum removal was achieved with immobilized cells in the presence of Tween ® 80. Investigation of PAH metabolites produced by 21198 revealed a complex mixture of hydroxylated compounds, quinones, and ring-fission products. Toxicity appeared to increase after bioremediation, manifesting as mortality and developmental effects in embryonic zebrafish. 21198's ability to rapidly transform PAHs of a variety of molecular structures and sizes suggests that 21198 can be a valuable microorganism for catalyzing PAH remediation. However, implementing further treatment processes to address toxic PAH metabolites should be pursued to help lower post-remediation toxicity in future studies.

Spatiotemporal Gradients of PAH Concentrations in Greek Cities and Associated Exposure Impacts

To study the spatiotemporal variability of particle-bound polycyclic aromatic hydrocarbons (PAHs) and assess their carcinogenic potential in six contrasting urban environments in Greece, a total of 305 filter samples were collected and analyzed. Sampling sites included a variety of urban background, traffic (Athens, Ioannina and Heraklion), rural (Xanthi) and near-port locations (Piraeus and Volos). When considering the sum of 16 U.S. EPA priority PAHs, as well as that of the six EU-proposed members, average concentrations observed across locations during summer varied moderately (0.4-2.2 ng m-3) and independently of the population of each site, with the highest values observed in the areas of Piraeus and Volos that are affected by port and industrial activities. Winter levels were significantly higher and more spatially variable compared to summer, with the seasonal enhancement ranging from 7 times in Piraeus to 98 times in Ioannina, indicating the large impact of PAH emissions from residential wood burning. Regarding benzo(a)pyrene (BaP), an IARC Group 1 carcinogen and the only EU-regulated PAH, the winter/summer ratios were 24-33 in Athens, Volos, Heraklion and Xanthi; 60 in Piraeus; and 480 in Ioannina, which is afflicted by severe wood-burning pollution events. An excellent correlation was observed between organic carbon (OC) and benzo(a)pyrene (BaP) during the cold period at all urban sites (r2 > 0.8) with stable BaP/OC slopes (0.09-0.14 × 10-3), highlighting the potential use of OC as a proxy for the estimation of BaP in winter conditions. The identified spatiotemporal contrasts, which were explored for the first time for PAHs at such a scale in the Eastern Mediterranean, provide important insights into sources and controlling atmospheric conditions and reveal large deviations in exposure risks among cities that raise the issue of environmental injustice on a national level.

Oil droplet fouling on lesser sandeel (Ammodytes marinus) eggshells does not enhance the crude oil induced developmental toxicity

The oil industry's expansion and increased operational activity at older installations, along with their demolition, contribute to rising cumulative pollution and a heightened risk of accidental oil spills. The lesser sandeel (Ammodytes marinus) is a keystone prey species in the North Sea and coastal systems. Their eggs adhere to the seabed substrate making them particularly vulnerable to oil exposure during embryonic development. We evaluated the sensitivity of sandeel embryos to crude oil in a laboratory by exposing them to dispersed oil at concentrations of 0, 15, 50, and 150 µg/L oil between 2 and 16 days post-fertilization. We assessed water and tissue concentrations of THC and tPAH, cyp1a expression, lipid distribution in the eyes, head and trunk, and morphological and functional deformities. Oil droplets accumulated on the eggshell in all oil treatment groups, to which the embryo responded by a dose-dependent rise in cyp1a expression. The oil exposure led to only minor sublethal deformities in the upper jaw and otic vesicle. The findings suggest that lesser sandeel embryos are resilient to crude oil exposure. The lowest observed effect level documented in this study was 36 µg THC/L and 3 µg tPAH/L. The inclusion of these species-specific data in risk assessment models will enhance the precision of risk evaluations for the North Atlantic ecosystems.

Exposure to individual polycyclic aromatic compounds impairs the cardiac performance of American lobster (Homarus americanus) larvae

The potential for oil spills poses a threat to marine organisms, the toxicity of which has been attributed primarily to polycyclic aromatic compounds (PACs). Predictive tools such as the target lipid model (TLM) have been developed to forecast and assess these risks. The aim of the present study was to characterize the cardiotoxicity of 10 structurally diverse PACs in American lobster (Homarus americanus) larvae by assessing heart rate following a 48 h exposure in a passive dosing system, and subsequently use the TLM framework to calculate a critical target lipid body burden (CTLBB) for bradycardia. Exposure to 8 of the 10 PACs resulted in concentration-dependent bradycardia, with phenanthrene causing the greatest effect. The TLM was able to effectively characterize bradycardia in American lobsters, and the cardiotoxic CTLBB value determined in this study is among the most sensitive endpoints included in the CTLBB database. This study is one of the first to apply the TLM to a cardiac endpoint and will improve predictive models for assessing sublethal impacts of oil spills on American lobster populations.

Fluorene-induced stress in the benthic oligochaete Tubifex tubifex: A multi-biomarker assessment of toxicological pathways and mechanisms under acute and subchronic exposures

This study examined the multifaceted impacts of fluorene exposure on Tubifex tubifex, encompassing acute (survival analysis and behavioral responses) and subchronic exposure regimens (antioxidant enzyme response and histopathology), molecular docking studies, and generalized read-across analysis. Survival analysis revealed concentration-dependent increases in toxicity over varying time intervals, with LC50 values decreasing from 30.072 mg/L at 24 h to 12.365 mg/L at 96 h, emphasizing the time-sensitive and concentration-responsive nature of the stressor. Behavioral responses were both concentration- and duration-dependent. While Erratic Movement and Clumping Tendency exhibited earlier responses (within 24 h) at lower concentrations, the wrinkling effect and mucus secretion) exhibited delayed onset, suggesting intricate regulatory mechanisms underlying adaptability to environmental challenges; moreover, the wrinkling effect was consistently induced at higher concentrations, indicating greater sensitivity to the toxic effects of fluorene. With sublethal environmentally relevant concentrations-1.24 mg/l and 2.47 mg/L i.e., 10% and 20% 96 h, respectively-the antioxidant enzyme response (i.e., upregulation of SOD, CAT, and GST) with increasing fluorene concentration, revealing a nonlinear, hormetic response, suggested adaptive protection at lower doses but inhibition at higher concentrations. Histopathological examination indicated that higher fluorene concentrations caused cellular proliferation, inflammation, and severe tissue damage in the digestive tract and body wall. Molecular docking studies demonstrated robust interactions between fluorene and major stress biomarker enzymes, disrupting their functions and inducing oxidative stress. Interactions with cytochrome c oxidase suggested interference with cellular energy production. Generalized Read-Across (GenRA) analysis unveiled shared toxicity mechanisms among fluorene and its analogs, involving the formation of reactive epoxides and the influence of cytochrome P450 enzymes. The diverse functional groups of these analogs, particularly chlorine-containing compounds, were implicated in toxicity through lipid peroxidation and membrane damage. Adverse outcome pathways and broader consequences for aquatic ecosystem health are discussed.

Zebrafish neuromast sensory system: Is it an emerging target to assess environmental pollution impacts?

Environmental pollution poses risks to ecosystems. Among these risks, one finds neurotoxicity and damage to the lateral line structures of fish, such as the neuromast and its hair cells. Zebrafish (Danio rerio) is recommended as model species to be used in ecotoxicological studies and environmental biomonitoring programs aimed at assessing several biomarkers, such as ototoxicity. However, little is known about the history of and knowledge gaps on zebrafish ototoxicity. Thus, the aim of the current study is to review data available in the scientific literature about using zebrafish as animal model to assess neuromast toxicity. It must be done by analyzing the history and publication category, world production, experimental design, developmental stages, chemical classes, neuromasts and hair cell visualization methods, and zebrafish strains. Based on the results, number, survival and fluorescence intensity of neuromasts, and their hair cells, were the parameters oftentimes used to assess ototoxicity in zebrafish. The wild AB strain was the most used one, and it was followed by Tübingen and transgenic strains with GFP markers. DASPEI was the fluorescent dye most often applied as method to visualize neuromasts, and it was followed by Yo-Pro-1 and GFP transgenic lines. Antibiotics, antitumorals, metals, nanoparticles and plant extracts were the most frequent classes of chemicals used in the analyzed studies. Overall, pollutants can harm zebrafish's mechanosensory system, as well as affect their behavior and survival. Results have shown that zebrafish is a suitable model system to assess ototoxicity induced by environmental pollution.

Embryonic exposures to cadmium and PAHs cause long-term and interacting neurobehavioral effects in zebrafish

Developmental exposure to either polycyclic aromatic hydrocarbons (PAHs) or heavy metals has been shown to cause persisting and overlapping neurobehavioral effects in animal models. However, interactions between these compounds have not been well characterized, despite their co-occurrence in a variety of environmental media. In two companion studies, we examined the effects of developmental exposure to cadmium (Cd) with or without co-exposure to prototypic PAHs benzo[a]pyrene (BaP, Exp. 1) or fluoranthene (FA, Exp. 2) using a developing zebrafish model. Zebrafish embryos were exposed to Cd (0-0.3 μM), BaP (0-3 μM), FA (0-1.0 μM), or binary Cd-PAH mixtures from 5 to 122 h post fertilization (hpf). In Exp. 1, Cd and BaP produced independent effects on an array of outcomes and interacting effects on specific outcomes. Notably, Cd-induced deficits in dark-induced locomotor stimulation were attenuated by BaP co-exposure in the larval motility test and BaP-induced hyperactivity was attenuated by Cd co-exposure in the adolescent novel tank test. Likewise, in Exp. 2, Cd and FA produced both independent and interacting effects. FA-induced increases on adult post-tap activity in the tap startle test were attenuated by co-exposure with Cd. On the predator avoidance test, FA- and 0.3 μM Cd-induced hyperactivity effects were attenuated by their co-exposure. Taken together, these data indicate that while the effects of Cd and these representative PAHs on zebrafish behavior were largely independent of one another, binary mixtures can produce sub-additive effects for some neurobehavioral outcomes and at certain ages. This research emphasizes the need for detailed risk assessments of mixtures containing contaminants of differing classes, and for clarity on the mechanisms which allow cross-class toxicant interactions to occur.

Dual effect of polyaromatic hydrocarbons on sarco(endo)plasmic reticulum calcium ATPase (SERCA) activity of a teleost fish (Oncorhynchus mykiss)

Polycyclic aromatic hydrocarbons (PAHs) are embryo- and cardiotoxic to fish that might be associated with improper intracellular Ca2+ management. Since sarco(endo)plasmic reticulum Ca2+-ATPase (SERCA) is a major regulator of intracellular Ca2+, the SERCA activity and the contractile properties of rainbow trout (Oncorhynchus mykiss) ventricle were measured in the presence of 3- and 4-cyclic PAHs. In unfractionated ventricular homogenates, acute exposure of SERCA to 0.1-1.0 μM phenanthrene (Phe), retene (Ret), fluoranthene (Flu), or pyrene (Pyr) resulted in concentration-dependent increase in SERCA activity, except for the Flu exposure, with maximal effects of 49.7-83 % at 1 μM. However, PAH mixture did not affect the contractile parameters of trout ventricular strips. Similarly, all PAHs, except Ret, increased the myotomal SERCA activity, but with lower effect (27.8-40.8 % at 1 μM). To investigate the putative chronic effects of PAHs on SERCA, the atp2a2a gene encoding trout cardiac SERCA was expressed in human embryonic kidney (HEK) cells. Culture of HEK cells in the presence of 0.3-1.0 μM Phe, Ret, Flu, and Pyr for 4 days suppressed SERCA expression in a concentration-dependent manner, with maximal inhibition of 49 %, 65 %, 39 % (P < 0.05), and 18 % (P > 0.05), respectively at 1 μM. Current findings indicate divergent effects of submicromolar PAH concentrations on SERCA: stimulation of SERCA activity in acute exposure and inhibition of SERCA expression in chronic exposure. The depressed expression of SERCA is likely to contribute to the embryo- and cardiotoxicity of PAHs by depressing muscle function and altering gene expression.

Historic distribution of Polycyclic Aromatic Compounds (PAC) in a Skagerrak fjord, Swedish west coast as reflected in a high-resolution sediment record and compared to the Environmental Quality Standards (EQS)

We present the historic distribution of Polycyclic Aromatic Compounds (PAC) in a Skagerrak fjord, a relatively unexploited area, on the Swedish west coast. PACs encompass various compounds, including PAHs, alkyl-PAHs, nitro-PAHs, and oxy-PAHs. These compounds, have environmental implications due to their harmful properties. Using a high-resolution sediment record, PAC variations including standard PAHs, nitro-PAHs and oxy-PAHs were investigated over the last approximately 170 years, comparing them with other European records. The sediment record reveals a significant increase in PAC levels during the 1940s-1950s, followed by peaks in the 1960s and 1970s, and a subsequent decrease in the 1980s. These trends align with industrial growth and evolving stronger environmental regulations in the region. The highest recorded concentration of PACs (1950-1970) reached levels comparable to present-day polluted urban environments. The study also compared PAH levels with EQS values. Results indicated that PAH levels exceeded EQS standards, potentially posing risks to sediment-dwelling organisms.

Limited impact of weathered residues from the Deepwater Horizon oil spill on the gut-microbiome and foraging behavior of sheepshead minnows (Cyprinodon variegatus)

The Deepwater Horizon disaster of April 2010 was the largest oil spill in U.S. history and exerted catastrophic effects on several ecologically important fish species in the Gulf of Mexico (GoM). Within fish, the microbiome plays a key symbiotic role in maintaining host health and aids in acquiring nutrients, supporting immune function, and modulating behavior. The aim of this study was to examine if exposure to weathered oil might produce significant shifts in fish gut-associated microbial communities as determined from taxa and genes known for hydrocarbon degradation, and whether foraging behavior was affected. The gut microbiome (16S rRNA and shotgun metagenomics) of sheepshead minnow (Cyprinodon variegatus) was characterized after fish were exposed to oil in High Energy Water Accommodated Fractions (HEWAF; tPAH = 81.1 ± 12.4 µg/L) for 7 days. A foraging behavioral assay was used to determine feeding efficiency before and after oil exposure. The fish gut microbiome was not significantly altered in alpha or beta diversity. None of the most abundant taxa produced any significant shifts as a result of oil exposure, with only rare taxa showing significant shifts in abundance between treatments. However, several bioindicator taxa known for hydrocarbon degradation were detected in the oil treatment, primarily Sphingomonas and Acinetobacter. Notably, the genus Stenotrophomonas was detected in high abundance in 16S data, which previously was not described as a core member of fish gut microbiomes. Data also demonstrated that behavior was not significantly affected by oil exposure. Potential low bioavailability of the oil may have been a factor in our observation of minor shifts in taxa and no behavioral effects. This study lays a foundation for understanding the microbiome of captive sheepshead minnows and indicates the need for further research to elucidate the responses of the fish gut-microbiome under oil spill conditions.

A complex mixture of polycyclic aromatic compounds causes embryotoxic, behavioral, and molecular effects in zebrafish larvae (Danio rerio), and in vitro bioassays

Polycyclic aromatic compounds (PACs) are prevalent in the environment, typically found in complex mixtures and high concentrations. Our understanding of the effects of PACs, excluding the 16 priority polycyclic aromatic hydrocarbons (16 PAHs), remains limited. Zebrafish embryos and in vitro bioassays were utilized to investigate the embryotoxic, behavioral, and molecular effects of a soil sample from a former gasworks site in Sweden. Additionally, targeted chemical analysis was conducted to analyze 87 PACs in the soil, fish, water, and plate material. CALUX® assays were used to assess the activation of aryl hydrocarbon and estrogen receptors, as well as the inhibition of the androgen receptor. Larval behavior was measured by analyzing activity during light and darkness and in response to mechanical stimulation. Furthermore, qPCR analyses were performed on a subset of 36 genes associated with specific adverse outcomes, and the total lipid content in the larvae was measured. Exposure to the sample resulted in embryotoxic effects (LC50 = 0.480 mg dry matter soil/mL water). The mixture also induced hyperactivity in darkness and hypoactivity in light and in response to the mechanical stimulus. qPCR analysis revealed differential regulation of 15 genes, including downregulation of opn1sw1 (eye pigmentation) and upregulation of fpgs (heart failure). The sample caused significant responses in three bioassays (ERα-, DR-, and PAH-CALUX), and the exposed larvae exhibited elevated lipid levels. Chemical analysis identified benzo[a]pyrene as the predominant compound in the soil and approximately half of the total PAC concentration was attributed to the 16 PAHs. This study highlights the value of combining in vitro and in vivo methods with chemical analysis to assess toxic mechanisms at specific targets and to elucidate the possible interactions between various pathways in an organism. It also enhances our understanding of the risks associated with environmental mixtures of PACs and their distribution during toxicity testing.

International Water Quality Guidelines for Polycyclic Aromatic Hydrocarbons: Advances to Improve Jurisdictional Uptake of Guidelines Derived Using The Target Lipid Model

A large number of different of polycyclic aromatic hydrocarbons (PAHs) have been found in environmental media, yet water quality guidelines (WQGs) are only available for a small subset of PAHs, limiting our ability to adequately assess environmental risks from these compounds. The target lipid model (TLM) was published over 20 years ago and has been extensively validated in the literature, but it has still not been widely adopted by jurisdictions to derive WQGs for PAHs. The goal of our study was to better align the methods for deriving TLM-based WQGs with international derivation protocols. This included updating the TLM with rescreened data to identify datapoints by which effect concentrations were estimated rather than measured, modernizing the statistics used to generate the hazard concentration, and testing the applicability of a chronic TLM model rather than using the acute-to-chronic ratio. The results show that the acute TLM model did not deviate substantially from the previous iteration, indicating that the model has reached a point of stability after over 20 years of testing and improvements. Water quality guidelines derived directly from a chronic TLM provided a similar level of protection as previous iterations of the TLM. The major advantage of adopting TLM-derived WQGs is the expanded list of PAH WQGs, which will allow a more fulsome quantification of environmental risks and the ability to apply the model to mixtures. Environ Toxicol Chem 2024;00:1-15. © 2023 SETAC.

Association between PAH and plastic fragments on Brazilian coast beaches: a baseline assessment

Plastic materials have many destinies on the environment, and one of them is its continuous fragmentation, originating microplastics (MP). MP act as an adsorption surface for organic pollutants like polycyclic aromatic hydrocarbons (PAH). Due to its toxic and harmful properties, 16 PAH are defined as priorities in studies. Several works have evaluated the occurrence of MP and PAH individually in environmental matrices, but just a few have investigated their association. The present study aims to investigate PAH occurrence, sources, and concentration in MP from beach sediments of eight Brazilian coastal states. Sixteen PAH were analyzed by gas chromatography, in which 14 PAH were detected, and PAH total concentration (ΣPAH) ranged from 0.25 to 71.60 ng g-1. In the North and Northeast regions, the low PAH concentrations in MP appear to be related to the intense hydrodynamic processes. Naphthalene levels on the Styrofoam were above the threshold effect level in two samples and near it on one; therefore, effects in the organisms might occur due to these PAH. The Southeast and South regions are the only ones with previous studies relating PAH with MP, and ΣPAH ranged from 0.34 to 2.52 ng g-1. According to the diagnostic ratios, the PAH sources were associated with industrial and port activities, untreated effluent disposal, and urban runoff by pluvial waters. The highest ΣPAH level was found in the Styrofoam samples, suggesting that this MP type might contribute considerable to PAH dispersion on Brazilian coast beaches.

Changes in Temperature Alter the Toxicity of Polycyclic Aromatic Compounds to American Lobster (Homarus americanus) Larvae

Polycyclic aromatic compounds (PACs) present in the water column are considered to be one of the primary contaminant groups contributing to the toxicity of a crude oil spill. Because crude oil is a complex mixture composed of thousands of different compounds, oil spill models rely on quantitative structure-activity relationships like the target lipid model to predict the effects of crude oil exposure on aquatic life. These models rely on input provided by single species toxicity studies, which remain insufficient. Although the toxicity of select PACs has been well studied, there is little data available for many, including transformation products such as oxidized hydrocarbons. In addition, the effect of environmental influencing factors such as temperature on PAC toxicity is a wide data gap. In response to these needs, in the present study, Stage I lobster larvae were exposed to six different understudied PACs (naphthalene, fluorenone, methylnaphthalene, phenanthrene, dibenzothiophene, and fluoranthene) at three different relevant temperatures (10, 15, and 20 °C) all within the biological norms for the species during summer when larval releases occur. Lobster larvae were assessed for immobilization as a sublethal effect and mortality following 3, 6, 12, 24, and 48 h of exposure. Higher temperatures increased the rate at which immobilization and mortality were observed for each of the compounds tested and also altered the predicted critical target lipid body burden, incipient median lethal concentration, and elimination rate. Our results demonstrate that temperature has an important influence on PAC toxicity for this species and provides critical data for oil spill modeling. More studies are needed so oil spill models can be appropriately calibrated and to improve their predictive ability. Environ Toxicol Chem 2023;42:2389-2399. © 2023 SETAC.

NSO-heterocyclic PAHs - Controlled exposure study reveals high acute aquatic toxicity

Environmental occurrence and hazardous nature of heterocyclic polyaromatic hydrocarbons (heterocyclic PAHs) has the potential to threaten the health of aquatic ecosystems. Here, we investigate the acute toxicity of heterocyclic PAHs (log KOW 3.7-6.9) to aquatic organisms: marine bacteria (Aliivibrio fischeri), freshwater green algae (Raphidocelis subcapitata), and water fleas (Daphnia magna) using passive dosing to maintain stable exposure. The membrane-water partition coefficient (KMW) of the heterocycles was measured to elucidate its relationship with toxicity. Our findings show that the tested heterocycles had little inhibitory effect on A. fischeri, while most compounds were highly toxic to R. subcapitata and D. magna. Toxicity generally increased with increasing KMW values, and nonpolar narcosis was identified as the most likely mode of toxic action of the heterocycles. Comparison of standard protocols with passive dosing emphasizes the importance of maintaining a constant concentration during toxicity testing, as very high losses occurred in standard tests and passive dosing experiments revealed higher toxicities. These results indicate a potentially high risk to aquatic life and call for more in-depth investigation of the (eco)toxic effects of NSO-PAHs.

Prenatal exposure to crude oil vapor reduces differentiation potential of rat fetal mesenchymal stem cells by regulating ERK1/2 and PI3K signaling pathways: Protective effect of quercetin

It has been indicated that crude oil vapor (COV) induces tissue damage by several molecular mechanisms. Quercetin (QT) as an important component of food with antioxidant properties has a protective role against cell toxicity caused by many pollutants. However, data related to the adverse effects of crude oil vapor (COV) on stem cell fate and differentiation and the role of quercetin (QT) in protecting stem cells against the toxicity caused by these pollutants is very limited. This study aimed to explore the protective effect of QT against the adverse effects of COV on fetal mesenchymal stem cells (fMSCs) differentiation. Twenty-four pregnant Wistar rats were categorized into 4 groups including the control, COV, COV+QT, and QT. Rats were exposed to COV from gestational day (GD) 0-15 and received QT by gavage. The fMSCs were isolated from fetuses, and cell proliferation, differentiation potential, expression of osteogenesis and adipogenesis-related genes, and phosphorylation of PI3K and ERK1/2 signaling proteins were evaluated. The results showed that COV reduced the proliferation and differentiation of fMSCs through the activation of PI3K and ERK1/2 signaling pathways. Also, COV significantly decreased the expression of osteonectin, ALP, BMP-6, Runx-2, PPARγ, and CREBBP genes in differentiated cells. QT treatment increased the proliferation and differentiation of fMSCs in COV-exposed rats. In conclusion, our findings suggest that prenatal exposure to COV impaired fMSCs differentiation and QT reduced the adverse effects of COV by regulating ERK1/2 and PI3K signaling pathways.

Advances in PAH mixture toxicology enabled by zebrafish

Polycyclic aromatic hydrocarbons (PAHs) are a class of organic compounds produced by a variety of petrogenic and pyrogenic sources. PAHs inherently occur in the environment in complex mixtures. The early life-stage zebrafish model is a valuable tool for high-throughput screening (HTS) for toxicity of complex chemical mixtures due to its rapid development, high fecundity, and superb sensitivity to chemical insult. Zebrafish are amenable to exposure to surrogate mixtures as well as extracts of environmental samples and effect-directed analysis. In addition to its utility to HTS, the zebrafish has proven an excellent model for assessing chemical modes of action and identifying molecular initiating and other key events in an Adverse Outcome Pathway framework. Traditional methods of assessing PAH mixture toxicity prioritize carcinogenic potential and lack consideration of non-carcinogenic modes of action, assuming a similar molecular initiating event for all PAHs. Recent work in zebrafish has made it clear that while PAHs belong to the same chemical class, their modes of action can be divergent. Future research should use zebrafish to better classify PAHs by their bioactivity and modes of action to better understand mixture hazards.

Evaluation of single and combined effects of mancozeb and metalaxyl on the transcriptional and biochemical response of zebrafish (Danio rerio)

Mancozeb and metalaxyl are fungicidal agents frequently used in combination to control fungi in crops that may affect non-target organisms when entering ecosystems. This study aims to evaluate the environmental effects of Mancozeb (MAN) and Metalaxyl (MET), alone and in combination, on zebrafish (Danio rerio) as an experimental model. The oxidative stress biomarkers and the transcription of genes involved in detoxification in zebrafish (Danio rerio) were assessed after co-exposure to MAN (0, 5.5, and 11 μg L^-1) and MET (0, 6.5, and 13 mg L^-1) for 21 days. Exposure to MAN and MET induced a significant increase in the expression of genes related to detoxification mechanisms (Ces2, Cyp1a, and Mt2). Although Mt1 gene expression increased in fish exposed to 11 μg L^-1 of MAN combined with 13 mg L^-1 of MET, Mt1 expression was down-regulated significantly in other experimental groups (p < 0.05). The combined exposure to both fungicides showed synergistic effects in the expression levels that are manifested mainly at the highest concentration. Although a significant (p < 0.05) increase in alkaline phosphatase (ALP) and transaminases (AST and ALT), catalase activities, the total antioxidant capacity, and malondialdehyde (MDA) contents in the hepatocytes of fish exposed to MAN and MET alone and in combination was detected, lactate dehydrogenase (LDH), gamma-glutamyl transferase (GGT) activities, and hepatic glycogen content decreased significantly (p < 0.05). Overall, these results emphasize that combined exposure to MET and MAN can synergistically affect the transcription of genes involved in detoxification (except Mt1 and Mt2) and biochemical indicators in zebrafish.

Recommendations for advancing media preparation methods used to assess aquatic hazards of oils and spill response agents

Laboratory preparation of aqueous test media is a critical step in developing toxicity information needed for oil spill response decision-making. Multiple methods have been used to prepare physically and chemically dispersed oils which influence test outcome, interpretation, and utility for hazard assessment and modeling. This paper aims to review media preparation strategies, highlight advantages and limitations, provide recommendations for improvement, and promote the standardization of methods to better inform assessment and modeling. A benefit of media preparation methods for oil that rely on low to moderate mixing energy coupled with a variable dilution design is that the dissolved oil composition of the water accommodation fraction (WAF) stock is consistent across diluted treatments.  Further, analyses that support exposure confirmation maybe reduced and reflect dissolved oil exposures that are bioavailable and amenable to toxicity modeling.  Variable loading tests provide a range of dissolved oil compositions that require analytical verification at each oil loading. Regardless of test design, a preliminary study is recommended to optimize WAF mixing and settling times to achieve equilibrium between oil and test media. Variable dilution tests involving chemical dispersants (CEWAF) or high energy mixing (HEWAF) can increase dissolved oil exposures in treatment dilutions due to droplet dissolution when compared to WAFs. In contrast, HEWAF/CEWAFs generated using variable oil loadings are expected to provide dissolved oil exposures more comparable to WAFs. Preparation methods that provide droplet oil exposures should be environmentally relevant and informed by oil droplet concentrations, compositions, sizes, and exposure durations characteristic of field spill scenarios. Oil droplet generators and passive dosing techniques offer advantages for delivering controlled constant or dynamic dissolved exposures and larger volumes of test media for toxicity testing. Adoption of proposed guidance for improving media preparation methods will provide greater comparability and utility of toxicity testing in oil spill response and assessment.

The Levels of Polycyclic Aromatic Hydrocarbons and Their Derivatives in Plasma and Their Effect on Mitochondrial DNA Methylation in the Oilfield Workers

This study focuses on the components and levels of polycyclic aromatic hydrocarbons (PAHs) and their derivatives (MPAHs and OPAHs) in plasma samples from 19 oil workers, pre- and post-workshift, and their exposure-response relationship with mitochondrial DNA (mtDNA) methylation. PAH, MPAH, OPAH, and platelet mtDNA methylation levels were determined using a gas chromatograph mass spectrometer (GC-MS) and a pyrosequencing protocol, respectively. The total plasma concentrations of PAHs in mean value were, respectively, 31.4 ng/mL and 48.6 ng/mL in pre- and post-workshift, and Phe was the most abundant (13.3 ng/mL in pre-workshift and 22.1 ng/mL in post-workshift, mean value). The mean values of total concentrations of MPAHs and OPAHs in the pre-workshift were 2.7 ng/mL and 7.2 ng/mL, while in the post-workshift, they were 4.5 ng/mL and 8.7 ng/mL, respectively. The differences in the mean MT-COX1, MT-COX2, and MT-COX3 methylation levels between pre- and post-workshift were 2.36%, 5.34%, and 0.56%. Significant (p < 0.05) exposure-response relationships were found between PAHs and mtDNA methylation in the plasma of workers; exposure to Anthracene (Ant) could induce the up-regulation of the methylation of MT-COX1 (β = 0.831, SD = 0.105, p < 0.05), and exposure to Fluorene (Flo) and Phenanthrene (Phe) could induce the up-regulation of methylation of MT-COX3 (β = 0.115, SD = 0.042, p < 0.05 and β = 0.036, SD = 0.015, p < 0.05, respectively). The results indicated that exposure to PAHs was an independent factor influencing mtDNA methylation.

Emission factors for polycyclic aromatic hydrocarbons from laboratory biomass-burning and their chemical transformations during aging in an oxidation flow reactor

Atmospheric polycyclic aromatic hydrocarbons (PAHs) can be emitted from different combustion sources including domestic biomass burning, internal combustion engines, and biomass burning (BB) in wild, prescribed, and agricultural fires. With climate warming and consequent global increases in frequency and severity of wildfires, BB is a dominant source of PAHs emitted into the atmosphere. In this study, six globally and regionally important and representative fuels (Alaskan peat, Moscow peat, Pskov peat, eucalyptus, Malaysian peat, and Malaysian agricultural peat) were burned under controlled conditions in the combustion chamber facility at the Desert Research Institute (DRI, Reno, NV, USA). Gas- and particle-phase BB emissions were aged in an oxidation flow reactor (OFR) to mimic five to sevendays of atmospheric aging. To sample gas- and particle-phase BB emissions, fresh and OFR-aged biomass-burning aerosols were collected on Teflon-impregnated glass fiber filters (TIGF) in tandem with XAD resin media for organic carbon speciation. The objectives of this study were to i) quantify the emission factors for 113 PAHs emitted from the combustion of the six selected fuels, ii) characterize the distribution of PAH compounds between gas and particle phases for these fuels, iii) identify the changes in PAHs during OFR-aging, and iv) evaluate toxicity potential with characterized compounds. We found that combustion emissions of gas-phase PAHs were more abundant (>80 % by mass) than particle-phase PAHs, for emissions from all combusted fuels. The mass fraction of substituted napthalenes in Moscow peat and Malaysian peat emissions were ∼70 % & 84 %, respectively, whereas in Eucalyptus the same fraction was <50 %, which indicates that these substituted compounds can be used as tracers for peat emissions. Mass concentrations of gas- and particle-phase PAHs were reduced by ∼70 % after OFR oxidation. However, the understanding of the fate of PAHs during OFR oxidation requires further investigations. Our results also indicate that the PAH toxicity of BB samples would be underestimated by 10-100 times if only the BaPeq for the 16 US EPA priority PAHs in the particle phase are included.

Molecular Dynamics Simulation Prediction of the Partitioning Constants (KH, Kiw, Kia) of 82 Legacy and Emerging Organic Contaminants at the Water-Air Interface

The tendency of organic contaminants (OCs) to partition between different phases is a key set of properties that underlie their human and ecological health impacts and the success of remediation efforts. A significant challenge associated with these efforts is the need for accurate partitioning data for an ever-expanding list of OCs and breakdown products. All-atom molecular dynamics (MD) simulations have the potential to help generate these data, but existing studies have applied these techniques only to a limited variety of OCs. Here, we use established MD simulation approaches to examine the partitioning of 82 OCs, including many compounds of critical concern, at the water-air interface. Our predictions of the Henry's law constant (K_H) and interfacial adsorption coefficients (K_iw, K_ia) correlate strongly with experimental results, indicating that MD simulations can be used to predict K_H, K_iw, and K_ia values with mean absolute deviations of 1.1, 0.3, and 0.3 logarithmic units after correcting for systematic bias, respectively. A library of MD simulation input files for the examined OCs is provided to facilitate future investigations of the partitioning of these compounds in the presence of other phases.

Hydroxylated polycyclic aromatic hydrocarbons possess inhibitory activity against alpha-glucosidase: An in vitro study using multispectroscopic techniques and molecular docking

Alpha-glucosidase (GAA) activity can be affected by exogenous substances. Hydroxylated polycyclic aromatic hydrocarbons (OH-PAHs) are typical metabolites of PAHs that can enter the body through various routes. The effects of 1-hydroxynaphthalene (1-OHNap) and 1-hydroxypyrene (1-OHPyr) on GAA activity and the potential mechanisms were investigated viamultispectroscopic methods and molecular docking. First-order derivative synchronous spectrofluorimetry was successfully applied to analyze the fluorescence quenching of GAA in the GAA-1-OHNap and GAA-1-OHPyr systems. 1-OHNap and 1-OHPyr had strong inhibitory effects on GAA activity. GAA could bind with 1-OHNap and 1-OHPyr in 1:1 mode with binding constants of 3.97 × 10⁴ and 9.42 × 10⁴ L/mol at 298 K. Hydrophobic interactions and hydrogen bonds played pivotal roles in the interactions. 1-OHNap was located closer to the active site of GAA than 1-OHPyr. This work suggests that the disturbance of glycometabolism by exogenous pollutants in the human body is worthy of attention and further investigation.

Alkyl-phenanthrenes in early life stage fish: differential toxicity in Atlantic haddock (Melanogrammus aeglefinus) embryos

Tricyclic polycyclic aromatic hydrocarbons (PAHs) are believed to be the primary toxic components of crude oil. Such compounds including phenanthrene are known to have direct effects on cardiac tissue, which lead to malformations during organogenesis in early life stage fish. We tested a suite of 13 alkyl-phenanthrenes to compare uptake and developmental toxicity in early life stage haddock (Melanogrammus aeglefinus) embryos during gastrulation/organogenesis beginning at 2 days post fertilization via passive dosing. The alkyl-phenanthrenes were tested at their solubility limits, and three of them also at lower concentrations. Measured body burdens were linearly related to measured water concentrations. All compounds elicited one or more significant morphological defects or functional impairment, such as decreased length, smaller eye area, shorter jaw length, and increased incidence of body axis deformities and eye deformities. The profile of developmental toxicities appeared unrelated to the position of alkyl substitution, and gene expression of cytochrome 1 a (cyp1a) was low regardless of alkylation. Mortality and sublethal effects were observed below the expected range for baseline toxicity, thus indicating excess toxicity. Additionally, PAH concentrations that resulted in toxic effects here were far greater than when measured in whole crude oil exposures that cause toxicity. This work demonstrates that, while these phenanthrenes are toxic to early life stage fish, they cannot individually account for most of the developmental toxicity of crude oil, and that other compounds and/or mixture effects should be given more consideration.

The Superfund Research Program Analytics Portal: linking environmental chemical exposure to biological phenotypes

The OSU/PNNL Superfund Research Program (SRP) represents a longstanding collaboration to quantify Polycyclic Aromatic Hydrocarbons (PAHs) at various superfund sites in the Pacific Northwest and assess their potential impact on human health. To link the chemical measurements to biological activity, we describe the use of the zebrafish as a high-throughput developmental toxicity model that provides quantitative measurements of the exposure to chemicals. Toward this end, we have linked over 150 PAHs found at Superfund sites to the effect of these same chemicals in zebrafish, creating a rich dataset that links environmental exposure to biological response. To quantify this response, we have implemented a dose-response modelling pipeline to calculate benchmark dose parameters which enable potency comparison across over 500 chemicals and 12 of the phenotypes measured in zebrafish. We provide a rich dataset for download and analysis as well as a web portal that provides public access to this dataset via an interactive web site designed to support exploration and re-use of these data by the scientific community at http://srp.pnnl.gov .

Target and Nontarget Screening of Organic Chemicals and Metals in Recycled Plastic Materials

Increased demand for recycling plastic has prompted concerns regarding potential introduction of hazardous chemicals into recycled goods. We present a broad screening of chemicals in 21 plastic flake and pellet samples from Canadian recycling companies. From target analysis, the organophosphorus ester flame retardants and plasticizers exhibited the highest detection frequencies (DFs) (5-100%) and concentrations (<DL-4,700 ng/g), followed by brominated/chlorinated flame retardants (<DL-2,150 ng/g, 5-76% DFs). The perfluoroalkyl acids were least detected at the lowest concentrations (<0.01-0.70 ng/g, 5-19% DFs). Using nontargeted analysis, 217 chemicals were identified as Level 1 (authentic standard) or 2 (library match), with estimated individual concentrations up to 1030 ng/g (highest: 2-hexyl hydroxy benzoate, 100% DF). Total (Σ60) element concentrations were between 0.005 and 2,980 mg/kg, with highest concentrations for calcium (2,980 mg/kg), sodium (617 mg/kg), and iron (156 mg/kg). Collectively >280 chemicals were detected in recycled plastic pellets and flakes, suggesting potential incorporation into recycled goods. Individual concentrations indicate unintentional trace contamination following European Union threshold limits for recycled granules (500 mg/kg) and waste plastic flakes (1,000 mg/kg), although do not reflect toxicological thresholds, if any. Our study highlights that while recycling addresses sustainability goals, additional screening of goods and products made from recycled plastics is needed to fully document potentially hazardous chemicals and exposure.

Coupling Environmental Whole Mixture Toxicity Screening with Unbiased RNA-Seq Reveals Site-Specific Biological Responses in Zebrafish

Passive sampling device (PSD) extracts paired with developmental toxicity assays in Danio Rerio (zebrafish) are excellent sensors for whole mixture toxicity associated with the bioavailable non-polar organics at environmental sites. We expand this concept by incorporating RNA-Seq in 48-h post fertilization zebrafish statically exposed to PSD extracts from two Portland Harbor Superfund Site locations: river mile 6.5W (RM 6.5W) and river mile 7W (RM 7W). RM 6.5W contained higher concentrations of polycyclic aromatic hydrocarbons (PAHs), but the diagnostic ratios of both extracts indicated similar PAH sourcing and composition. Developmental screens determined RM 6.5W to be more toxic with the most sensitive endpoint being a "wavy" notochord malformation. Differential gene expression from exposure to both extracts was largely parallel, although more pronounced for RM 6.5W. When compared to the gene expression associated with individual chemical exposures, PSD extracts produced some gene signatures parallel to PAHs but were more closely matched by oxygenated-PAHs. Additionally, differential expression, reminiscent of the wavy notochord phenotype, was not accounted for by either class of chemical, indicating the potential of other contaminants driving mixture toxicity. These techniques offer a compelling method for non-targeted hazard characterization of whole mixtures in an in vivo vertebrate system without requiring complete chemical characterization.

Polycyclic aromatic hydrocarbons (PAHs): Updated aspects of their determination, kinetics in the human body, and toxicity

Polycyclic aromatic hydrocarbons (PAHs) are legacy pollutants of considerable public health concern. Polycyclic aromatic hydrocarbons arise from natural and anthropogenic sources and are ubiquitously present in the environment. Several PAHs are highly toxic to humans with associated carcinogenic and mutagenic properties. Further, more severe harmful effects on human- and environmental health have been attributed to the presence of high molecular weight (HMW) PAHs, that is PAHs with molecular mass greater than 300 Da. However, more research has been conducted using low molecular weight (LMW) PAHs). In addition, no HMW PAHs are on the priority pollutants list of the United States Environmental Protection Agency (US EPA), which is limited to only 16 PAHs. However, limited analytical methodologies for separating and determining HMW PAHs and their potential isomers and lack of readily available commercial standards make research with these compounds challenging. Since most of the PAH kinetic data originate from animal studies, our understanding of the effects of PAHs on humans is still minimal. In addition, current knowledge of toxic effects after exposure to PAHs may be underrepresented since most investigations focused on exposure to a single PAH. Currently, information on PAH mixtures is limited. Thus, this review aims to critically assess the current knowledge of PAH chemical properties, their kinetic disposition, and toxicity to humans. Further, future research needs to improve and provide the missing information and minimize PAH exposure to humans.

Oxygenated and Nitrated Polycyclic Aromatic Hydrocarbons: Sources, Quantification, Incidence, Toxicity, and Fate in Soil—A Review Study

The genotoxicity, mutagenesis, and carcinogenic effects of polycyclic aromatic hydrocarbon (PAH) derivatives may exceed the parent PAHs. However, their influence on the soil environment has not been explored to a large extent. Oxygenated polycyclic aromatic hydrocarbons (OPAHs) and nitrated polycyclic aromatic hydrocarbons (NPAHs) are typical polar substituted compounds. We offer a review of the literature on the sources, quantification, incidence, toxicity, and transport of these compounds in soil. Although their environmental concentrations are lower than those of their parent compounds, they exert higher toxicity. Both types of substances are basically related to carcinogenesis. OPAHs are not enzymatically activated and can generate reactive oxygen species in biological cells, while NPAHs have been shown to be mutagenic, genotoxic, and cytotoxic. These compounds are largely derived from the transformation of PAHs, but they behave differently in soil because of their higher molecular weight and dissimilar adsorption mechanisms. Therefore, specialized knowledge of model derivatives is required. We also made recommendations for future directions based on existing research. It is expected that the review will trigger scientific discussions and provide a research basis for further study on PAH derivatives in the soil environment.

Oxygenated polycyclic aromatic hydrocarbons in food: toxicity, occurrence and potential sources

Oxygenated polycyclic aromatic hydrocarbons (OPAHs) are polycyclic aromatic hydrocarbons (PAHs) functionalized with at least one carbonyl group and are generally thought to be more toxic than PAHs. In this review, the physical-chemical properties, toxicity, occurrence, and potential sources of OPAHs in food were comprehensively discussed. The toxicities of 1,2-naphthoquinone, 1,4-naphthoquinone, 6H-benzo[cd]pyren-6-one, benzo[a]anthracene-7,12-quinone and 9,10-phenanthrenequinone were prominent among the OPAHs. Both 1,4-naphthoquinone and 1,2-naphthoquinone exhibited strong genotoxicity, cytotoxicity, and developmental toxicity. 6H-benzo[cd]pyren-6-one and benzo[a]anthracene-7,12-quinone showed high genotoxicity and cardiovascular toxicity. Although 9,10-phenanthrenequinone showed no genotoxicity, it exhibited almost the strongest cytotoxicity. For the majority of foods, the concentrations of OPAHs and PAHs were on the same order of magnitude. OPAHs tend to be positively correlated with the corresponding PAH concentrations in oil and fried food, while for barbequed food and seafood, no obvious correlation was found. In addition, 9-fluorenone, 9,10-anthraquinone, benzanthrone and 1,2-acenaphthenequinone had high abundance in food. Environmental pollution, food composition, storage conditions, heating methods, and other treatments influence the accumulation of OPAHs in food. Furthermore, oxygen and water played an important role in the transformation from PAHs to OPAHs. In short, this review guides the evaluation and further reduction of OPAH-related health risks in food.