Identifying Organic Toxicants in Sediment Using Effect-Directed Analysis: A Combination of Bioaccessibility-Based Extraction and High-Throughput Midge Toxicity Testing

Recent advances in bioassays for assessing the toxicity of environmental contaminants in effect-directed analysis

Chemical cocktails in the environment can cause adverse impacts on ecosystems and human health even at low concentrations. Effect-directed analysis (EDA) has proven to be very valuable in identifying key toxic substances in environmental mixtures. For this, it is important to carefully select accurate bioassays from a wide range of tests for EDA when applying it to actual environmental samples. This article reviews studies published from 2014 to 2023 that have applied EDA and summarizes the bioassays and their corresponding biological effects. A total of 127 studies were selected from 591 publications evaluating the toxic effects of environmental samples, including wastewater, surface water, and sediments. Here, bioassays used in EDA are summarized, including the assays that measure specific receptor-mediated modes of action (MOA), induction of xenobiotic metabolism pathways, and induction of adaptive stress response pathways using either in vitro or in vivo bioassays. Also, the identified substances using EDA are discussed based on their MOA. The importance of EDA in establishing a comprehensive approach for the detection of environmental contaminants using bioanalytical methods is emphasized. The current limitations and benefits of using EDA in practical applications are outlined and strategies for moving forward are proposed.

Identifying and prioritizing organic toxicants in treated flowback and produced water from shale gas exploitation sites using an integrative effect-directed analysis and nontarget screening method

The use of hydraulic fracturing in shale gas exploitation has generated substantial amount of flowback and produced water (FPW), and ecological risk of these highly complex chemical mixtures has raised worldwide concern. Herein, an integrative effect-directed analysis (EDA) and nontarget screening (NTS) workflow was developed to identify and prioritize main toxicants in the treated FPW (T-FPW). The workflow included sample extraction and fractionation, zebrafish embryo toxicity tests, target and nontarget chemical analyses, and toxicity prioritization and confirmation using toxicological priority index (ToxPi). Results showed that less hydrophobic compounds (log Kow < 3.7) which were used in fracturing fluid and their degradation products were the potentially high-risk toxicants in T-FPW. Thirty-nine target compounds identified in toxic fraction explained 4.82% of the mortality. Additional 584 nontarget contaminants were annotated by NTS. Risk prioritization was achieved for 470 identified contaminants with ecotoxicity data available using a ToxPi method. Six nontarget toxicants were identified with higher ecological risks than all target contaminants, and their presence in FPW were confirmed using reference standards. A principal component analysis of NTS features revealed that EDA fractionation reduced mixture complexity and focused toxicant screening, which significantly improved NTS efficiency, highlighting advantages of integrative EDA and NTS for mixture risk assessment.

Role of sediment particle size in cypermethrin toxicity to Chironomus dilutus and Hyalella azteca: insights from bioavailability and exposure pathways

Variation in sediment particle properties gives rise to diverse settling velocities and distances, leading to distinct distributions of particle sizes in field sediments, while the impact of particle size on sediment toxicity is scarcely known. We investigated the variations in spiked-sediment toxicity across different particle sizes (<20 μm, 63-180 μm, 180-500 μm, and original) with cypermethrin, one of the main toxicity contributors in sediment from South China, as the target compound and two invertebrates Chironomus dilutus and Hyalella azteca as the testing species. Cypermethrin in fine sediments was more toxic than in coarse sediments, as evidenced by lower LC50 values, even though the desorption rate from fine sediments was slower than that from coarse sediments. The LC50 and LC25 (μg per g OC) values of cypermethrin for C. dilutus and H. azteca differed by 5- and 4-fold, respectively, across sediments. The variation in toxicity was only partially reduced when the LC50 values were based on bioavailable concentrations derived from biomimetic extraction methods, implying that bioavailability was not responsible for the enhanced toxicity of fine particle sizes. The ingestion of fine sediment particles bound with cypermethrin may significantly contribute to sediment toxicity to benthic and epibenthic invertebrates, underscoring the importance of evaluating multiple exposure pathways in sediment toxicity assessments.

Progress, applications, and challenges in high-throughput effect-directed analysis for toxicity driver identification - is it time for HT-EDA?

The rapid increase in the production and global use of chemicals and their mixtures has raised concerns about their potential impact on human and environmental health. With advances in analytical techniques, in particular, high-resolution mass spectrometry (HRMS), thousands of compounds and transformation products with potential adverse effects can now be detected in environmental samples. However, identifying and prioritizing the toxicity drivers among these compounds remain a significant challenge. Effect-directed analysis (EDA) emerged as an important tool to address this challenge, combining biotesting, sample fractionation, and chemical analysis to unravel toxicity drivers in complex mixtures. Traditional EDA workflows are labor-intensive and time-consuming, hindering large-scale applications. The concept of high-throughput (HT) EDA has recently gained traction as a means of accelerating these workflows. Key features of HT-EDA include the combination of microfractionation and downscaled bioassays, automation of sample preparation and biotesting, and efficient data processing workflows supported by novel computational tools. In addition to microplate-based fractionation, high-performance thin-layer chromatography (HPTLC) offers an interesting alternative to HPLC in HT-EDA. This review provides an updated perspective on the state-of-the-art in HT-EDA, and novel methods/tools that can be incorporated into HT-EDA workflows. It also discusses recent studies on HT-EDA, HT bioassays, and computational prioritization tools, along with considerations regarding HPTLC. By identifying current gaps in HT-EDA and proposing new approaches to overcome them, this review aims to bring HT-EDA a step closer to monitoring applications.

Revealing the distribution of synthetic musks in Chinese estuarine sediments driven by natural and anthropogenic factors

Synthetic musks (SMs) commonly used in personal care products can accumulate in the estuarine environment, but influencing factors on their distribution at large-scale region remain largely unexplored. Herein, surface sediment samples from 18 main estuaries of China and two river outlets in the Yangtze River Estuary were collected to discern the spatial and temporal variations of SMs. Moreover, fourteen influencing factors consisting of natural and anthropogenic parameters were scrutinized and their significance were analyzed by using Spearman's rank correlation and Random Forest. The widespread distribution of SMs were observed in Chinese estuarine sediments with the levels ranging from < reporting limit to 28 ng g-1 on a basis of dry weight (mean: 3.5 ng g-1). Predominated polycyclic musks shared similar sources both spatially and temporally. Positive correlation was found between SMs and total organic carbon in sediments, whereas the SM distribution was strongly influenced by regional anthropogenic activities. Regional population density was the primary influencing factor, followed by gross domestic product per unit area and wet deposition of particulate matters. A good correlation between SMs and water quality category indicated SMs could serve as an indicator for water quality. To the best of our knowledge, this is the first study to identify the main influencing factors on SM distribution in estuarine sediments, aiming to better understand the distribution and fate of emerging organic chemicals in the estuarine environment.

Evidence from In Situ Bioassays and Suspect Analysis Revealed the Region-Specific Aquatic Risk across Socioeconomic Gradients in China

Various contaminants are present in aquatic environment and pose potential threats to pelagic and benthic organisms, calling for effective risk assessment. Traditional risk assessments based on target analysis are useful when the principal contaminants responsible for ecological risk are known; however, these approaches become challenging when dealing with chemical mixtures. In addition, the compositions of chemical mixtures often differ in regions with different levels of socioeconomic development, requiring risk assessment methods that are applicable under different pollution scenarios. Herein, in situ bioassays were conducted with two native species, Chinese rare minnows (Gobiocypris rarus) and Asian clams (Corbicula fluminea), in economically developed watersheds in China (Pearl River Basin (PRB) and Taihu Lake Basin (THB)) and agriculture-dominated Poyang Lake Basin (PYB). Significant lethal and sublethal effects (e.g., neurotoxicity, reproductive toxicity, and metabolic and oxidative stress) were observed in fish and clams irrespective of economic gradients. Notably, ecological effects differed significantly between water and sediment phases within the same region. Target (98 contaminants) and suspect screening (942 contaminants) revealed regional-specific characteristics. Ecological risk assessments using a weight of evidence approach demonstrated that both water and sediment in the PRB were at moderate to high risk, as was the sediment in the less developed PYB. However, the characteristics of mixture pollution varied greatly among regions. Suspect screening identified many pollutants that are not regularly monitored but are present at high environmental concentrations and are linked to local industrial production. These distinct mixture risk characteristics across different basins suggest that mitigating aquatic pollution requires region-specific management measures.

Deep Learning Bridged Bioactivity, Structure, and GC-HRMS-Readable Evidence to Decipher Nontarget Toxicants in Sediments

Identifying causative toxicants in mixtures is critical, but this task is challenging when mixtures contain multiple chemical classes. Effect-based methods are used to complement chemical analyses to identify toxicants, yet conventional bioassays typically rely on an apical and/or single endpoint, providing limited diagnostic potential to guide chemical prioritization. We proposed an event-driven taxonomy framework for mixture risk assessment that relied on high-throughput screening bioassays and toxicant identification integrated by deep learning. In this work, the framework was evaluated using chemical mixtures in sediments eliciting aryl-hydrocarbon receptor activation and oxidative stress response. Mixture prediction using target analysis explained <10% of observed sediment bioactivity. To identify additional contaminants, two deep learning models were developed to predict fingerprints of a pool of bioactive substances (event driver fingerprint, EDFP) and convert these candidates to MS-readable information (event driver ion, EDION) for nontarget analysis. Two libraries with 121 and 118 fingerprints were established, and 247 bioactive compounds were identified at confidence level 2 or 3 in sediment extract using GC-qToF-MS. Among them, 12 toxicants were analytically confirmed using reference standards. Collectively, we present a "bioactivity-signature-toxicant" strategy to deconvolute mixtures and to connect patchy data sets and guide nontarget analysis for diverse chemicals that elicit the same bioactivity.

Species sensitivity distribution for nonylphenol: Acute toxicity and ecological risk in Bohai Region

Nonylphenol (NP), a main byproduct of nonylphenol polyethoxylates (NPEs) degradation, is prevalent across diverse environmental settings. Given its widespread presence, evaluating the ecological risks associated with NP in coastal waters and sediments is essential for the protection of the marine environment. This study evaluates the acute toxicity of NP on ten representative aquatic species from the Bohai Sea, determining the Aquatic Life Criteria (ALC) through two distinct methods. The Criteria Maximum Concentration (CMC) for NP in seawater was established at 12.0 μg/L, with a Predicted No-Effect Concentration (PNEC) for water at 15.2 μg/L and for sediment at 33.3 μg/kg. Additionally, a tiered ecological risk assessment (ERA) of both surface seawater and sediment in the Bohai Sea revealed significant ecological risks at various sediment sites. These results offer crucial insights for assessing the ecological risks to coastal ecosystem and provide foundational data necessary for informed environmental protection and management strategies.

High-Efficiency Effect-Directed Analysis Leveraging Five High Level Advancements: A Critical Review

Organic contaminants are ubiquitous in the environment, with mounting evidence unequivocally connecting them to aquatic toxicity, illness, and increased mortality, underscoring their substantial impacts on ecological security and environmental health. The intricate composition of sample mixtures and uncertain physicochemical features of potential toxic substances pose challenges to identify key toxicants in environmental samples. Effect-directed analysis (EDA), establishing a connection between key toxicants found in environmental samples and associated hazards, enables the identification of toxicants that can streamline research efforts and inform management action. Nevertheless, the advancement of EDA is constrained by the following factors: inadequate extraction and fractionation of environmental samples, limited bioassay endpoints and unknown linkage to higher order impacts, limited coverage of chemical analysis (i.e., high-resolution mass spectrometry, HRMS), and lacking effective linkage between bioassays and chemical analysis. This review proposes five key advancements to enhance the efficiency of EDA in addressing these challenges: (1) multiple adsorbents for comprehensive coverage of chemical extraction, (2) high-resolution microfractionation and multidimensional fractionation for refined fractionation, (3) robust in vivo/vitro bioassays and omics, (4) high-performance configurations for HRMS analysis, and (5) chemical-, data-, and knowledge-driven approaches for streamlined toxicant identification and validation. We envision that future EDA will integrate big data and artificial intelligence based on the development of quantitative omics, cutting-edge multidimensional microfractionation, and ultraperformance MS to identify environmental hazard factors, serving for broader environmental governance.

Prioritizing Organic Pollutants for Shale Gas Exploitation: Life Cycle Environmental Risk Assessments in China and the US

Environmental impacts associated with shale gas exploitation have been historically underestimated due to neglecting to account for the production or the release of end-of-pipe organic pollutants. Here, we assessed the environmental impacts of shale gas production in China and the United States using life cycle assessment. Through data mining, we compiled literature information on organic pollutants in flowback and produced water (FPW), followed by assessments using USEtox to evaluate end-of-pipe risks. Results were incorporated to reveal the life cycle risks associated with shale gas exploitation in both countries. China exhibited higher environmental impacts than the US during the production phase. Substantially different types of organic compounds were observed in the FPW between two countries. Human carcinogenic and ecological toxicity attributed to organics in FPW was 3 orders of magnitude higher than that during the production phase in the US. Conversely, in China, end-of-pipe organics accounted for approximately 52%, 1%, and 47% of the overall human carcinogenic, noncarcinogenic, and ecological impacts, respectively. This may be partially limited by the quantitative data available. While uncertainties exist associated with data availability, our study highlights the significance of integrating impacts from shale gas production to end-of-pipe pollution for comprehensive environmental risk assessments.

Microbial mechanisms of C/N/S geochemical cycling during low-water-level sediment remediation in urban rivers

Low-water-level regulation has been effectively implemented in the restoration of urban river sediments in Guangzhou City, China. Further investigation is needed to understand the microbial mechanisms involved in pollutant degradation in low-water-level environments. This study examined sediment samples from nine rivers, including low-water-level rivers (LW), tidal waterways (TW), and enclosed rivers (ER). Metagenomic high-throughput sequencing and the Diting pipeline were utilized to investigate the microbial mechanisms involved in sediment C/N/S geochemical cycling during low-water-level regulation. The results reveal that the degree of pollution in LW sediment is lower compared to TW and ER sediment. LW sediment exhibits a higher capacity for pollutant degradation and elimination of black, odorous substances due to its stronger microbial methane oxidation, nitrification, denitrification, anammox, and oxidation of sulfide, sulfite, and thiosulfate. Conversely, TW and ER sediment showcase greater microbial methanogenesis, anaerobic fermentation, and sulfide generation abilities, leading to the persistence of black, odorous substances. Factors such as grit and silt content, nitrate, and ammonia concentrations impacted microbial metabolic pathways. Low-water-level regulation improved the micro-environment for functional microbes, facilitating pollutant removal and preventing black odorous substance accumulation. These findings provide insights into the microbial mechanisms underlying low-water-level regulation technology for sediment restoration in urban rivers.

Synthetic musks in the natural environment: Sources, occurrence, concentration, and fate-A review of recent developments (2010-2023)

Synthetic musks (SMs) have served as cost-effective substitutes for natural musk compounds in personal care and daily chemical products for decades. Their widespread use has led to their detection in various environmental matrices, raising concerns about potential risks. Despite numerous studies on SM levels in different natural environments, a systematic review of their contemporary presence is lacking. This review aims to address this gap by summarising recent research developments on SMs in diverse natural environments, including river water, lake water, seawater, estuarine water, groundwater, snow, meltwater, sediments, aquatic suspended matter, soils, sands, outdoor air, and atmospheric particulate matter. Covering the period from 2010 to 2023, the review focuses on four SM categories: nitro, polycyclic, macrocyclic, and alicyclic. It systematically examines their sources, occurrences, concentrations, spatial and temporal variations, and fate. The literature reveals widespread detection of SMs in the natural environment (freshwater and sediments in particular), with polycyclic musks being the most studied group. Both direct (e.g., wastewater discharges) and indirect (e.g., human recreational activities) sources contribute to SM presence. Levels of SMs vary greatly among studies with higher levels observed in certain regions, such as sediments in Southeast Asia. Spatial and temporal variations are also evident. The fate of SMs in the environment depends on their physicochemical properties and environmental processes, including bioaccumulation, biodegradation, photodegradation, adsorption, phase exchange, hydro-dilution effects. Biodegradation and photodegradation can decrease SM levels, but may produce more persistent and eco-toxic products. Modelling approaches have been employed to analyse SM fate, especially for indirect processes like photodegradation or long-distance atmospheric transport. Future studies should further investigate the complex fate if SMs and their environmental influence. This review enhances understanding of SM status in the natural environment and supports efforts to control environmental contamination.

Occurrence and Ecological Risk of Alkylamine Triazines in Chinese Estuarine Sediments: An Emerging Class of Persistent, Mobile, and Toxic Substances

Identifying persistent, mobile, and toxic (PMT) substances from synthetic chemicals is critical for chemical management and ecological risk assessment. Inspired by the triazine analogues (e.g., atrazine and melamine) in the original European Union's list of PMT substances, the occurrence and compositions of alkylamine triazines (AATs) in the estuarine sediments of main rivers along the eastern coast of China were comprehensively explored by an integrated strategy of target, suspect, and nontarget screening analysis. A total of 44 AATs were identified, of which 23 were confirmed by comparison with authentic standards. Among the remaining tentatively identified analogues, 18 were emerging pollutants not previously reported in the environment. Tri- and di-AATs were the dominant analogues, and varied geographic distributions of AATs were apparent in the investigated regions. Toxic unit calculations indicated that there were acute and chronic risks to algae from AATs on a large geographical scale, with the antifouling biocide cybutryne as a key driver. The assessment of physicochemical properties further revealed that more than half of the AATs could be categorized as potential PMT and very persistent and very mobile substances at the screening level. These results highlight that AATs are a class of PMT substances posing high ecological impacts on the aquatic environment and therefore require more attention.

Effect-Directed Analysis Combined with Nontarget Screening to Identify Unmonitored Toxic Substances in the Environment

Effect-directed analysis (EDA) combined with nontarget screening (NTS) has established a valuable tool for the identification of unmonitored toxic substances in environmental samples. It consists of three main steps: (1) highly potent fraction identification, (2) toxicant candidate selection, and (3) major toxicant identification. Here, we discuss the methodology, current status, limitations, and future challenges of EDA combined with NTS. This method has been applied successfully to various environmental samples, such as sediments, wastewater treatment plant effluents, and biota. We present several case studies and highlight key results. EDA has undergone significant technological advancements in the past 20 years, with the establishment of its key components: target chemical analysis, bioassays, fractionation, NTS, and data processing. However, it has not been incorporated widely into environmental monitoring programs. We provide suggestions for the application of EDA combined with NTS in environmental monitoring programs and management, with the identification of further research needs.

Identification and Prioritization of Environmental Organic Pollutants: From an Analytical and Toxicological Perspective

Exposure to environmental organic pollutants has triggered significant ecological impacts and adverse health outcomes, which have been received substantial and increasing attention. The contribution of unidentified chemical components is considered as the most significant knowledge gap in understanding the combined effects of pollutant mixtures. To address this issue, remarkable analytical breakthroughs have recently been made. In this review, the basic principles on recognition of environmental organic pollutants are overviewed. Complementary analytical methodologies (i.e., quantitative structure-activity relationship prediction, mass spectrometric nontarget screening, and effect-directed analysis) and experimental platforms are briefly described. The stages of technique development and/or essential parts of the analytical workflow for each of the methodologies are then reviewed. Finally, plausible technique paths and applications of the future nontarget screening methods, interdisciplinary techniques for achieving toxicant identification, and burgeoning strategies on risk assessment of chemical cocktails are discussed.

Ecological risk of galaxolide and its transformation product galaxolidone: evidence from the literature and a case study in Guangzhou waterways

Galaxolidone (HHCB-lac) is a major transformation product of the commonly used synthetic musk galaxolide (HHCB) and is ubiquitous in the environment along with the parent compound. Although many studies have shown the harmful effects of HHCB, little attention has been paid to the potential ecological risk of HHCB-lac. Herein, we reviewed the concentrations and ratios of HHCB and HHCB-lac (HHCB-lac : HHCB) in different media reported in the literature, derived the predicted no-effect concentrations (PNECs) for the two compounds using ECOSAR predictions and species sensitivity distribution (SSD) estimates, and assessed their ecological risks in the aquatic environment. The literature data indicated that HHCB-lac and HHCB were generally present in the environment at ratios of 0.01-10. Using the derived PNECs (2.14 and 18.4 μg L-1 for HHCB and HHCB-lac, respectively), HHCB in the aquatic environment was assessed to have medium to high risks, while HHCB-lac was assessed to have low risks. Furthermore, we carried out a case study on the occurrence and ecological risks of HHCB and HHCB-lac in Guangzhou waterways. The concentrations of the two compounds in Guangzhou waterways ranged from 20 to 2620 ng L-1 and 3 to 740 ng L-1, respectively, and the ratios were in the range of 0.15 to 0.64. The field study data also showed medium to high risks of HHCB and low risks of HHCB-lac. Additionally, the endocrine effects of HHCB and HHCB-lac were confirmed by Endocrine Disruptome, which calls for greater scrutiny of the potential effects of HHCB and HHCB-lac on human health.

Influence of dissolved organic carbon on multimedia distribution and toxicity of fipronil and its transformation products in lotic waterways

Environmental fate and ecological impacts of fipronil and its transformation products (FIPs) in aquatic environment have caused worldwide attention, however, the influence of dissolved organic carbon (DOC) on multimedia distribution, bioavailability, and toxicity of FIPs in field waterways was largely unknown. Here, we collected 11 companion water and sediment samples along a lotic stream in Guangzhou, South China. FIPs were ubiquitous with total water concentrations ranging from 1.22 to 43.2 ng/L (14.8 ± 12.9 ng/L) and fipronil sulfone was predominant in both water and sediment. More than 70% of FIPs in aqueous phase were bound to DOC and the K_DOC values of FIPs were approximately 1-2 orders of magnitude higher than K_d-s/K_OC, emphasizing the significance of DOC in phase partitioning and transport of FIPs in aquatic environment. Water and sediment samples were more toxic to Chironomus dilutus than Hyallela azteca, and FIPs (especially fipronil sulfone) pronouncedly contributed toxicity to C. dilutus. Toxic units (TU) based on freely dissolved concentrations in water determined by solid phase microextraction significantly improved toxicity estimation of FIPs to the invertebrates compared to TUs based on aqueous concentrations. The present study highlights the significance of DOC association on fate and ecological risk of hydrophobic insecticides in lotic ecosystem.

An integrated screening strategy for novel AhR agonist candidate identification and toxicity confirmation in sediments

Organic contaminants showing aryl hydrocarbon receptor (AhR) agonist activity are commonly detected in areas disturbed by intense human activities and they can initiate a variety of biochemical, physiological, and toxicological effects. A new integrated screening strategy for AhR agonist candidate identification and toxicity confirmation was developed to characterize the AhR-active pollutants in sediments of the contaminated Daqing River basin (DRB) in North China. The specific objectives were to (i) determine the concentrations of known AhR agonists, (ii) identify the novel AhR agonist candidates from nontarget screening (NTS) with structure alerts, computational toxicology (CompTox) Dashboard bioassays, and in silico predictions, and (iii) evaluate contributions of AhR agonists to the overall potencies and characterize the distribution and source of these pollutants. Significant AhR-mediated potencies were observed in all sediment extracts by in vitro bioassays. Concentrations of polar target chemicals in sediment extracts were much lower than nonpolar target chemicals. A total of 19 known AhR agonists explained 11.3 % to 49.1 % of bioassay-derived AhR-mediated potencies and polychlorinated biphenyls (PCB) 126 and PCB169 were found to contribute significantly to the total effects. 21 compounds screened from NTS by AhR-related structure alerts and further confirmed toxicity by high-throughput bioassays and in silico predictions were selected as AhR agonist candidates. Most of them were substituted PAHs, biphenyls, quinones, substituted phenols and heterocyclic compounds, and they primarily originated from nearby manufacturing industries. Of these compounds, 1-methy-pyrene exhibited significant AhR-mediated potency. Follow up studies should focus on toxicological mechanism, source, and fate of these novel AhR agonists in water environment.

Bioassay-based identification and removal of target and suspect toxicants in municipal wastewater: Impacts of chemical properties and transformation

Municipal wastewater contains numerous chemicals and transformation products with highly diverse physiochemical properties and intrinsic toxicity; thus, it is imperative but challenging to identify major toxicants. Herein, toxicity identification evaluation (TIE) was applied to identify major toxicants in a typical municipal wastewater treatment plant (WWTP). Impacts of chemical properties on the removal of contaminants and toxicity at individual treatment stages were also examined. The WWTP influent caused 100% death of Daphnia magna and zebrafish embryos, and toxicity characterization suggested that organics, metals, and volatiles all contributed to the toxicity. Toxicity identification based on 189 target and approximately one-thousand suspect chemicals showed that toxicity contributions of organic contaminants, metals, and ammonia to D. magna were 77%, 4%, and 19%, respectively. Galaxolide, pyrene, phenanthrene, benzo[a]anthracene, fluoranthene, octinoxate, silver, and ammonia were identified as potential toxicants. Comparatively, the detected transformation products elicited lower toxicity than their respective parent contaminants. In contrast, the analyzed contaminants showed negligible contributions to the toxicity of zebrafish embryos. Removal efficiencies of these toxicants in WWTP were highly related to their hydrophobicity. Diverse transformation and removal efficiencies of contaminants in WWTPs may influence the chemical compositions in effluent and ultimately the risk to aquatic organisms in the receiving waterways.

Effect-Directed Analysis Based on the Reduced Human Transcriptome (RHT) to Identify Organic Contaminants in Source and Tap Waters along the Yangtze River

Since a large number of contaminants are detected in source waters (SWs) and tap waters (TWs), it is important to perform a comprehensive effect evaluation and key contributor identification. A reduced human transcriptome (RHT)-based effect-directed analysis, which consisted of a concentration-dependent RHT to reveal the comprehensive effects and noteworthy pathways and systematic identification of key contributors based on the interactions between compounds and pathway effects, was developed and applied to typical SWs and TWs along the Yangtze River. By RHT, 42% more differentially expressed genes and 33% more pathways were identified in the middle and lower reaches, indicating heavier pollution. Hormone and immune pathways were prioritized based on the detection frequency, sensitivity, and removal efficiency, among which the estrogen receptor pathway was the most noteworthy. Consistent with RHT, estrogenic effects were widespread along the Yangtze River based on in vitro evaluations. Furthermore, 38 of 100 targets, 39 pathway-related suspects, and 16 estrogenic nontargets were systematically identified. Among them, diethylstilbestrol was the dominant contributor, with the estradiol equivalent (EEQ) significantly correlated with EEQ_water. In addition, zearalenone and niclosamide explained up to 54% of the EEQ_water. The RHT-based EDA method could support the effect evaluation, contributor identification, and risk management of micropolluted waters.

Spiking organic chemicals onto sediments for ecotoxicological analyses: an overview of methods and procedures

Laboratory testing with spiked sediments with organic contaminants is a valuable tool for ecotoxicologists to study specific processes such as effects of known concentrations of toxicants, interactions of the toxicants with sediment and biota, and uptake kinetics. Since spiking of the sediment may be performed by using different strategies, a plethora of procedures was proposed in the literature for spiking organic chemicals onto sediments to perform ecotoxicological analyses. In this paper, we reviewed the scientific literature intending to characterise the kind of substrates that were used for spiking (i.e. artificial or field-collected sediment), how the substrates were handled before spiking and amended with the organic chemical, how the spiked sediment was mixed to allow the homogenisation of the chemical on the substrate and finally how long the spiked sediment was allowed to equilibrate before testing. What emerged from this review is that the choice of the test species, the testing procedures and the physicochemical properties of the organic contaminant are the primary driving factors affecting the selection of substrate type, sediment handling procedures, solvent carrier and mixing method. Finally, we provide recommendations concerning storage and characterization of the substrate, equilibrium times and verification of both equilibration and homogeneity.

Identification of toxicity factors and causal analysis of toxicity in surface sediments from Liaohe river basin, Northeast China using an effect guidance strategy

Sediments play a pivotal role in maintaining the aquatic ecological status of rivers. However, the determination of the key toxicants that consider the combined effects of all sediment-related contaminants are still challenging and necessary for an appropriate sediment risk assessment. The effects of sediments on aquatic organisms have been reported in Liaohe River, but their key toxicity factors are not well known. To determine the key toxicity factors, twenty-six surface sediment samples from Liaohe River tributaries in Northeast China were collected. Acute toxicity test of midge larvae results showed that 6 of 26 tributaries had obvious toxic effects, with survival rates of 37%-57% (p < 0.05). The masking test showed that the main pollutants in the surface sediments of T7 and T16 were metals, that of T8 was an organic pollutant, those of T19 and T26 were organic pollutants and ammonia, and those of T17 were heavy metal and ammonia. Chemical analysis showed that the relatively high concentrations of ammonia were only presented in surface sediments of T17, T19, and T26, with PTU of 1.5, 1.2 and 1.1, respectively, whereas heavy metals were markedly high in surface sediments from T7 and T16, with PTU of 0.92 and 0.61, respectively. Interestingly, the observed toxicity in surface sediments agreed with the toxicity predicted by chemical analysis Moreover, the significant correlation between the survival and volume ratio of the sediment and overlying water confirmed ammonia nitrogen was key toxicity factor in T17, T19, and T26, whereas Cu was the key toxicity factor in T7 that cause the biological toxicity. In conclusion, the major toxic factors of ammonia and copper in the sediments were identified. Moreover, our study suggested that effect guidance strategy was an effective method for sediment quality assessment.

In-situ biological effects, bioaccumulation, and multi-media distribution of organic contaminants in a shallow lake

Anthropogenic activity-impacted aquatic environment contains a complex mixture of contaminants, and ecological risk assessment solely based on chemical analysis is insufficient and biological assessment is required. However, traditional assessment heavily relies on laboratory bioassays, which may cause uncertainty due to inevitable laboratory-related artifact. A self-designed in-situ bioassay system was successfully applied to simultaneously evaluate water and sediment toxicity by co-exposure of two native species, Chinese rare minnows (Gobiocypris rarus) and Asian clams (Corbicula fluminea) in Tai Lake Basin, China. In-situ exposure caused pronouncedly lethal and sublethal effects (i.e., metabolic and oxidative stress, neurotoxicity, reproductive toxicity) on both fish and clams. Meanwhile, multi-media distribution of organic contaminants in water-sediment-biota system was analyzed. Besides hydrophobicity, metabolism was recognized as an influential factor on phase distribution of contaminants in water-fish and sediment-clam systems. Traditional hazard quotient (HQ) method based on environmental concentrations of 98 contaminants showed bias in risk assessment. Instead, a weight of evidence method by integrating three lines of evidence, including in-situ survival, enhanced integrated biomarker response values and environmental concentrations, successfully differentiate high- and moderate-risk sites in the shallow lakes. The present study incorporated in-situ bioassays into risk assessment using a weight of evidence approach, which reduced uncertainty in decision-making.

Point or non-point source: Toxicity evaluation using m-POCIS and zebrafish embryos in municipal sewage treatment plants and urban waterways

Municipal sewage treatment plants (STPs) have been regarded as an important source of organic contaminants in aquatic environment. To assess the impact of STPs on occurrence and toxicity of STP-associated contaminants in receiving waterways, a novel passive sampler modified from polar organic chemical integrative sampler (m-POCIS) was deployed at the inlet and outlet of a STP and several upstream and downstream sites along a river receiving STP effluent in Guangzhou, China. Eighty-seven contaminants were analyzed in m-POCIS extracts, along with toxicity evaluation using zebrafish embryos. Polycyclic musks were the predominant contaminants in both STP and urban waterways, and antibiotics and current-use pesticides (e.g., neonicotinoids, fiproles) were also ubiquitous. The m-POCIS extracts from downstream sites caused significant deformity in embryos, yet the toxicity could not be explained by the measured contaminants, implying the presence of nontarget stressors. Sewage treatment process substantially reduced embryo deformity, chemical oxygen demand, and contamination levels of some contaminants; however, concentrations of neonicotinoids and fiproles increased after STP treatment, possibly due to the release of chemicals from perturbed sludge. Source identification showed that most of the contaminants found in urban waterways were originated from nonpoint runoff, while cosmetics factories and hospitals were likely point sources for musks and antibiotics, respectively. Although the observed embryo toxicity could not be well explained by target contaminants, the present study showed a promising future of using passive samplers to evaluate chemical occurrence and aquatic toxicity concurrently. Zebrafish embryo toxicity significantly decreased after sewage treatment, but higher toxicity was observed for downstream samples, demonstrating that urban runoff may produce detrimental effects to aquatic life, particularly in rainy season. These results highlight the relevance of monitoring nonpoint source pollution along with boosting municipal sewage treatment infrastructure.

Cis-bifenthrin inhibits cortisol and aldosterone biosynthesis in human adrenocortical H295R cells via cAMP signaling cascade

Cis-bifenthrin (cis-BF) is a common-used pyrethroid insecticide frequently detected in environmental and biological matrices. Mounting evidence highlights the endocrine disrupting effects of cis-BF due to anti-estrogenic or anti-androgenic activity. However, little is known about the exposure effects of cis-BF on adrenal cortex function. In this study, effects of cis-BF on biosynthesis of adrenal steroids, as well as the potential mechanisms were investigated in human adrenocortical carcinoma (H295R) cells. Cis-BF decreased basal production levels of cortisol and aldosterone, as well as cAMP-induced production of cortisol. Both he basal and cAMP-stimulated transcriptional levels of several steroidogenic genes were significantly down-regulated by cis-BF. As an important rate-limiting enzyme in steroidogenesis, the protein level of StAR was prohibited by cis-BF on both basal and cAMP-induced conditions. Intracellular level of cAMP was significantly reduced by cis-BF. Overall, these data suggest that cis-BF may inhibit the biosynthesis of cortisol and aldosterone via disrupting cAMP signaling cascade.

Novel polar AhR-active chemicals detected in sediments of an industrial area using effect-directed analysis based on in vitro bioassays with full-scan high resolution mass spectrometric screening

Studies investigating aryl hydrocarbon receptor (AhR)-active compounds in the environment typically focus on non- and mid-polar substances, such as PAHs; while, information on polar AhR agonists remains limited. Here, we identified polar AhR agonists in sediments collected from the inland creeks of an industrialized area (Lake Sihwa, Korea) using effect-directed analysis combined with full-scan screening analysis (FSA; using LC-QTOFMS). Strong AhR-mediated potencies were observed for the polar and latter fractions of RP-HPLC (F3.5-F3.8) from sediment organic extracts in the H4IIE-luc in vitro bioassays. FSA was performed on the corresponding fractions. Twenty-eight tentative AhR agonists were chosen using a five-step process. Toxicological confirmation using bioassay revealed that canrenone, rutaecarpine, ciprofloxacin, mepanipyrim, genistein, protopine, hydrocortisone, and medroxyprogesterone were significantly active. The relative potencies of these AhR-active compounds compared to that of benzo[a]pyrene ranged from 0.00002 to 2.0. Potency balance analysis showed that polar AhR agonists explained, on average, ~6% of total AhR-mediated potencies in samples. Some novel polar AhR agonists also exhibited endocrine-disrupting potentials capable of binding to estrogen and glucocorticoid receptors, as identified by QSAR modeling. In conclusion, the focused studies on distributions, sources, fate, and ecotoxicological effects of novel polar AhR agonists in the environment are necessary.

Identifying bioaccessible suspect toxicants in sediment using adverse outcome pathway directed analysis

Chemical mixtures are a common occurrence in contaminated sediment and determining causal relationship between sediment contamination and adverse outcomes is challenging. The bioavailability and choice of bioassay endpoints played important roles in elucidating causality. As such, bioaccessibility-based XAD extraction and adverse outcome pathway (AOP) guided bioassays were incorporated into an effect-directed analysis to more effectively determine sediment causality. XAD extracts of sediments from urban waterways in Guangzhou, China were examined using cell viability bioassays with four human tumor cells from lung, liver, breast, and bone marrow. Pronounced effects to SH-SY5Y cells were noted, thus neurotoxicity was subsequently focused in the AOP-guided bioassays. Intracellular calcium influx, mitochondrial membrane potential inhibition, reactive oxygen species generation, and cell viability were utilized as evidence for neurotoxicity AOP-guided analysis. Suspect toxicants were identified in active fractions using GC-MS. Toxicity confirmation was performed by evaluating toxicity contributions of the candidates to the pathway. Cypermethrin, bisphenol A, galaxolide, tonalide, and versalide were found as the major stressors across key events of the studied pathway. Moreover, good correlations among key events validated the feasibility of method to predict in vivo response, suggesting that considering bioavailability and AOP improved environmental relevance for toxicant identification in a complex mixture.

Multiple Bioassays and Targeted and Nontargeted Analyses to Characterize Potential Toxicological Effects Associated with Sediments of Masan Bay: Focusing on AhR-Mediated Potency

An enhanced, multiple lines of evidence approach was applied to assess potential toxicological effects associated with polluted sediments. Two in vitro bioassays (H4IIE-luc and Vibrio fischeri) and three in vivo bioassays (microalgae: Isochrysis galbana and Phaeodactylum tricornutum; zebrafish embryo: Danio rerio) were applied. To identify causative chemicals in samples, targeted analyses (polycyclic aromatic hydrocarbons (PAHs), styrene oligomers (SOs), and alkylphenols) and nontargeted full-scan screening analyses (FSA; GC- and LC-QTOFMS) were performed. First, great AhR-mediated potencies were observed in midpolar and polar fractions of sediment extracts, but known and previously characterized AhR agonists, including PAHs and SOs could not fully explain the total potencies of samples. Enoxolone was identified as a novel AhR agonist in a highly potent sediment fraction by use of FSA. Enoxolone has a relative potency of 0.13 compared to benzo[a]pyrene (1.0) in the H4IIE-luc bioassay. Nonylphenols associated with membrane damage that influenced the viability of the microalgae were also observed. Finally, inhibitions of bioluminescence of V. fischeri and lethality of D. rerio embryos were strongly related to nonpolar compounds. Overall, the present work addressed assay- and end point-specific variations and sensitivities for potential toxicities of mixture samples, warranting a significant utility of the "multiple lines of evidence" approach in ecological risk assessment.

Smarter Sediment Screening: Effect-Based Quality Assessment, Chemical Profiling, and Risk Identification

Sediments play an essential role in the functioning of aquatic ecosystems but simultaneously retain harmful compounds. However, sediment quality assessment methods that consider the risks caused by the combined action of all sediment-associated contaminants to benthic biota are still underrepresented in water quality assessment strategies. Significant advancements have been made in the application of effect-based methods, but methodological improvements can still advance sediment risk assessment. The present study aimed to explore such improvements by integrating effect-monitoring and chemical profiling of sediment contamination. To this end, 28 day life cycle bioassays with Chironomus riparius using intact whole sediment cores from contaminated sites were performed in tandem with explorative chemical profiling of bioavailable concentrations of groups of legacy and emerging sediment contaminants to investigate ecotoxicological risks to benthic biota. All contaminated sediments caused effects on the resilient midge C. riparius, stressing that sediment contamination is ubiquitous and potentially harmful to aquatic ecosystems. However, bioassay responses were not in line with any of the calculated toxicity indices, suggesting that toxicity was caused by unmeasured compounds. Hence, this study underlines the relevance of effect-based sediment quality assessment and provides smarter ways to do so.

Understanding the bioavailability of pyrethroids in the aquatic environment using chemical approaches

Pyrethroids are a class of commonly used insecticides and are ubiquitous in the aquatic environment in various regions. Aquatic toxicity of pyrethroids was often overestimated when using conventional bulk chemical concentrations because of their strong hydrophobicity. Over the last two decades, bioavailability has been recognized and applied to refine the assessment of ecotoxicological effects of pyrethroids. This review focuses on recent advances in the bioavailability of pyrethroids, specifically in the aquatic environment. We summarize the development of passive sampling and Tenax extraction methods for assessing the bioavailability of pyrethroids. Factors affecting the bioavailability of pyrethroids, including physicochemical properties of pyrethroids, and quality and quantity of organic matter, were overviewed. Various applications of bioavailability on the assessment of bioaccumulation and acute toxicity of pyrethroids were also discussed. The final section of this review highlights future directions of research, including development of standardized protocols for measurement of bioavailability, establishment of bioavailability-based toxicity benchmarks and water/sediment quality criteria, and incorporation of bioavailability into future risk assessment and management actions.