Temporal and spatial characteristics of PAHs in oysters from the Pearl River Estuary, China during 2015-2020

The effects of perfluoroalkyl substance pollution on microbial community and key metabolic pathways in the Pearl River Estuary

The extensive use of perfluoroalkyl substances (PFASs) has raised significant concerns regarding their adverse environmental implications. However, the understanding of their behaviors and biological effects in natural estuarine ecosystems remain limited. This study employed a multidisciplinary approach integrating chemical analysis, biological sequencing, and statistical modeling to comprehensively investigate the distribution of PFASs, as well as their intrinsic relationship with microbial community in the Pearl River Estuary (PRE), a rapidly urbanized area. Our findings demonstrate that the total PFAS concentrations ranged from 52-127 ng L-1 in water, and 2-70 μg kg-1 dry weight in sediment, with notably distinct compositions across habitats. Aquatic microbial communities exhibited higher sensitivity to environmental variables, including PFAS concentrations, attributed to increased stochasticity and reduced spatial turnover. Conversely, sediments harbored microbial communities with higher phylogenetic diversity, rendering them less susceptible to PFAS-induced stress. Furthermore, PFAS concentrations significantly affected microbial carbon, nitrogen, and phosphorus cycling, predominantly through indirect alterations in characteristic genus composition. Importantly, noteworthy variations in impacts were observed between perfluorinated carboxylic acids (PFCAs) and perfluorinated sulfonic acids (PFSAs), which might contingent upon C-F bond dissociation energies. The findings shed light on PFAS ecological roles and interaction patterns with microbial communities in human-impacted estuarine environments.

Bioaccumulation and potential human health risks of PAHs in marine food webs: A trophic transfer perspective

Polycyclic aromatic hydrocarbons (PAHs) are persistent pollutants in aquatic environments that can accumulate in marine organisms and pose potential health risks to humans through trophic transfer in the food webs. However, the accumulation and health risks of PAHs in organisms at different trophic levels remain unclear. This study investigated the accumulation and trophic transfer of PAHs in 40 marine organisms from Beibu Gulf (China), and assessed their health risks. Utilizing the trophic level spectrum constructed with stable isotope methods, the organisms were categorized into three trophic levels: Omnivorous (15.00 %), low-level carnivorous (67.50 %), and mid-level carnivorous (17.50 %). The contamination levels of total PAHs in these organisms ranged from "mild pollution" to "moderate pollution", with all organisms exhibiting significant PAH accumulation (Bioconcentration factor value > 2000). Total PAH concentrations increased with higher trophic levels, following the trend of mid-level carnivores > low-level carnivores > omnivores. Notably, only three PAH compounds (Nap, Fla and Phe) showed biomagnification effects, while the others exhibited trophic dilution. Carcinogenic risk assessment indicated an "Unacceptable risk" level for all populations, with the highest risk due to consumption of mid-level carnivorous. These findings offer new insights into the accumulation and health risks of PAHs from a trophic transfer perspective.

Crab urine as biomonitoring tools for pollution: A state-of-the-art review of methods, organic contaminant levels, and comparisons between spilled and unspilled areas

This study constitutes a systematic review endeavoring to elucidate the methodologies pertinent to the extraction and analysis of organic contaminants, specifically focusing on crab urine. Although research is limited, crabs serve as invaluable bioindicators and biomonitors due to their unique habitat in sediment-rich areas where aquatic contaminants commonly accumulate. Despite the well-documented harmful effects of substances like PCBs, OCPs, PBDEs, and pesticides on the nervous and endocrine systems, our review found that existing studies have predominantly focused on PAHs such as pyrene, benzo(a)pyrene, and naphthalene oi spilled and unspilled areas. One reason for this research gap is the misconception that collecting crab urine is challenging, a notion perpetuated by the lack of detailed methodologies in the literature. The research gap hinders comparing contamination levels and trends. Limited, infrequent studies highlight the urgent need for comprehensive investigations to enhance understanding of ecological impacts and improve environmental monitoring.

Distribution and sources of polycyclic aromatic hydrocarbons in cascade reservoir sediments: influence of anthropogenic activities and reservoir hydrology

The construction of dams has caused disruptions to river connectivity, leading to alterations in the deposition of hydrophobic organic contaminants in reservoir sediments. Further investigation is warranted to explore the impact of cascade reservoirs with differing hydrological characteristics on polycyclic aromatic hydrocarbons (PAHs) distribution in sediment. This study examines the presence of 30 PAHs in the sediments collected from six cascade reservoirs situated in the Wujiang River basin during January and July 2017. The results showed that Σ30 PAHs ranged from 455-3000 ng/g dw (mean 1030 ng/g dw). Anthropogenic activities and reservoir hydrology determined the distribution trend of PAHs in sediments, with an overall increase from upstream to midstream and then a decrease downstream. The PAH levels were highly linked to the secondary industry (P < 0.05). This was further supported by the relationship between the PAH emissions from coal combustion and traffic sources analyzed by the positive matrix factorization model and economic parameters in the wet season (P < 0.01). At the same time, reservoir age (RA) showed a positive correlation with PAH concentrations (P < 0.05), while hydraulic retention time (HRT) exhibited a negative correlation with PAH levels (P = 0.03). The relationship between total organic carbon (TOC) and PAHs in stream sediments worldwide was nonlinear (P < 0.01), with PAH concentrations initially rising and then falling as TOC levels increased. Concerns regarding carcinogenic risk were raised due to contributions from coal and vehicular sources, with the risk increasing with RA.

Analysis of the UV filter Benzophenone-3 assimilation in Crossostrea gigas oysters post-exposure in a controlled environment by LC-MS/MS

Benzophenone-3 (BP-3), utilized as a UV filter in cosmetic products, is an emerging contaminant that constitutes a threat to natural resources and environmental health. This study investigated the assimilation of the UV filter BP-3 in Crassostrea gigas oysters collected in Florianópolis, Santa Catarina, Brazil. Lyophilized oyster tissue extracts were prepared using the QuEChERS method, and LC-MS/MS was employed to determine the BP-3 concentration in the samples. The method was applied to specimens intentionally exposed to two concentrations of the contaminant, for different periods of exposure (1 and 7 days). Samples from treatment 1 (T1) were exposed to a concentration of 1 μg L-1 of the BP-3 standard, and samples from treatment 2 (T2) were exposed to a concentration of 100 μg L-1 of the BP-3 standard. The results revealed rapid absorption of BP-3, with an increase of 126% for lower concentrations, reaching 1.13 μg of BP-3 per gram of oyster tissue, and 17% for higher concentrations, reaching 34.6 μg of BP-3 per gram of oyster tissue after 7 days. The presence of BP-3 even in samples not directly exposed to the contaminant indicates its widespread environmental distribution. The rapid bioaccumulation suggests the need to consider seasonal variations, such as increased tourism in the summer. The validated analytical method demonstrated efficacy in quantifying BP-3, providing an integrated approach for long-term monitoring of pollution levels and their dynamic variations over time. In addition, variation in BP-3 levels in the samples may be related to transport patterns influenced by tides and discharges from septic system, highlighting the need to improve wastewater treatment. These findings underscore the necessity for continuous biomonitoring and effective environmental management to safeguard the health of marine ecosystems and humans.

Air pollution prevention in central China: Effects on particulate-bound PAHs from 2010 to 2018

Long-term trends in particulate-bound polycyclic aromatic hydrocarbon (PAH) concentrations in air in Zhengzhou (a severely polluted city in central China) between 2010 and 2018 were studied to assess the effectiveness of an air pollution prevention and control action plan (APPCAP) implemented in 2013. The PM2.5, sum of 16 PAHs (Σ16 PAHs), benzo[a]pyrene (BaP), and BaP toxic equivalent concentrations were high before 2013 but 41%, 77%, 77%, and 78% lower, respectively, after the APPCAP. The maximum daily Σ16 PAHs concentration between 2014 and 2018 was 338 ng/m3, 65% lower than the maximum of 961 ng/m3 between 2010 and 2013. The ratio between the Σ16 PAHs concentrations in winter and summer decreased over time and was 8.0 in 2011 and 1.5 in 2017. The most abundant PAH was benzo[b]fluoranthene, for which the 9-year mean concentration was 14 ± 21 ng/m3 (15% of the Σ16 PAHs concentration). The mean benzo[b]fluoranthene concentration decreased from 28 ± 27 ng/m3 before to 5 ± 4 ng/m3 after the APPCAP (an 83% decrease). The mean daily BaP concentrations were 0.1-62.8 ng/m3, and >56% exceeded the daily standard limit of 2.5 ng/m3 for air. The BaP concentration decreased from 10 ± 8 ng/m3 before to 2 ± 2 ng/m3 after the APPCAP (a 77% decrease). Diagnostic ratios and positive matrix factorization model results indicated that coal combustion and vehicle exhausts were important sources of PAHs throughout the study period, contributing >70% of the Σ16 PAHs concentrations. The APPCAP increased the relative contribution of vehicle exhausts from 29% to 35% but decreased the Σ16 PAHs concentration attributed to vehicle exhausts from 48 to 12 ng/m3. The PAH concentration attributed to vehicle exhausts decreased by 79% even though vehicle numbers strongly increased, indicating that pollution caused by vehicles was controlled well. The relative contribution of coal combustion remained stable but the PAH concentration attributed to coal combustion decreased from 68 ng/m3 before to 13 ng/m3 after the APPCAP. Vehicles made dominant contributions to the incremental lifetime cancer risk (ILCRs) before and after the APPCAP even though the APPCAP decreased the ILCRs by 78%. Coal combustion was the dominant source of PAHs but contributed only 12-15% of the ILCRs. The APPCAP decreased PAH emissions and changed the contributions of different sources of PAHs, and thus strongly affected the overall toxicity of PAHs to humans.

Differentiation and decreased genetic diversity in field contaminated oysters Crassostrea hongkongensis: Identification of selection signatures

The extent to which chemical contamination affects the population structure and genetic diversity of natural populations remains elusive. Here, we used the whole-genome resequencing and transcriptome to diagnose the effects of long-term exposure to multiple elevated chemical pollutants on the population differentiation and genetic diversity in oysters Crassostrea hongkongensis in a typically polluted Pearl River Estuary (PRE) of Southern China. Population structure revealed an obvious differentiation between the PRE oysters and those collected from a nearby clean Beihai (BH) individuals, while no significant differentiation was observed among individuals collected from the three pollution sites within PRE due to the high gene flow. The decreased genetic diversity in the PRE oysters reflected the long-term effects of chemical pollutants. Selective sweeps between BH and PRE oysters revealed that chemical defensome genes, including glutathione S-transferase, zinc transporter, were responsible for their differentiation, sharing common metabolic process of other pollutants. Combined with the genome-wide association analysis, 25 regions containing 77 genes were identified to be responsible for the direct selection regions of metals. Linkage disequilibrium blocks and haplotypes within these regions provided the biomarkers of permanent effects. Our results provide important insights to the genetic mechanisms underlying the rapid evolution under chemical contamination in marine bivalves.

Spatiotemporal trends of ultraviolet absorbents in oysters from the Pearl River Estuary, south China during 2015-2020

Ultraviolet absorbents (UVAs) are widely used in various industrial materials, pharmaceuticals, and personal care products, resulting in their frequent occurrences in sediment, water, and biota. However, our understanding of the spatiotemporal characteristics and long-term contamination status of UVAs is still limited. Here, a 6-year biomonitoring study with oysters during wet and dry seasons was conducted to examine the annual, seasonal, and spatial characteristics of UVAs in the Pearl River Estuary (PRE), China. The concentrations of Σ₆UVA ranged from 9.1 to 119 (geometric mean ± standard deviation: 31 ± 22) ng/g dry wt. and peaked in 2018. Significant spatiotemporal variations in UVA contamination were observed. The concentrations of UVAs in oysters during the wet season were higher than the dry season, and concentrations in the more industrialized eastern coast were higher than the western coast (p < 0.05). Environmental factors, including precipitation, temperature, and salinity in water significantly impacted the UVA bioaccumulation in the oysters. The present study highlights that long-term biomonitoring with oysters provided valuable insight in the magnitude and seasonal variation of UVAs in this highly dynamic estuary.

Variation in the concentration of particulate Pd in the Nandu River Estuary during spring-neap tides

Estuaries are environmental systems with great resource potential and environmental benefits. This study investigates the role of particulate palladium (Pd) in the Nandu River Estuary in the enrichment of estuarine geochemical processes during spring-neap tides. Particulate Pd was found to show different characteristics during spring-neap tides, with the hydrodynamic condition being one of the key factors causing the difference. In addition, particulate Pd showed a decreasing trend while moving from the mouth to the upstream. The highest value of particulate Pd was 35.32 ng L^-1, which occurred at the intersection of the mainstream and the branch during the neap tide, and the lowest value was 0.86 ng·L^-1, which occurred in the far mouth area during the spring tide. The concentrations of particulate Pd during the neap and spring tides were 5.53 (1.01-35.32) ng·L^-1 and 2.33 (0.86-5.22) ng·L^-1, respectively. With the exception of stations 1, 5, 10, 11, and 15, the concentration of particulate Pd during the neap tide was greater than that during the spring tide. The variation in the particulate Pd was inconsistent between the spring tide and the neap tide, and the fluctuation in each study section during the neap tide was greater than that during the spring tide. In addition, since the emissions from catalytic converter are in the form of nanoparticles, they are difficult to be dissolve in natural water, and therefore, the concentration of particulate Pd was obviously greater in the waters near large bridges and main roads. An analysis of the physical and chemical properties of the water showed that Cl^- easily combined with dissolved Pd and was one of the important factors that affected the concentration of particulate Pd. In addition, DO and Eh had little effect on the change in the particulate Pd during the tidal cycle, and pH had a significant positive correlation with particulate Pd.

Two-dimensional gas chromatography coupled to isotope ratio mass spectrometry for determining high molecular weight polycyclic aromatic hydrocarbons in sediments

The accuracy of compound-specific isotope analysis (CSIA) of trace-level pollutants in complex environmental samples has always been limited by two main challenges: poor chromatographic separation and insufficient amounts of analytes. In this study, a two-dimensional gas chromatography-isotope ratio mass spectrometry (2DGC-IRMS) system was constructed for compound-specific δ¹³C analysis of high molecular weight polycyclic aromatic hydrocarbons (HMW-PAHs) in estuarine/marine sediments. This construction occurred through hyphenating an extra gas chromatography system (GC) to a conventional GC-IRMS using a commercially available multi-column switching-cryogenic trapping system (MCS-CTS). Compared with the previous 2DGC-IRMS strategy, which utilizes a Deans Switch device, the newly implemented 2DGC-IRMS scheme resulted in online purification of target analytes as well as enriched them online via duplicate injection and cryogenic trapping in CTS; this resultingly lowered the limits of detection (LOD) of CSIA. To improve the sample transfer efficiency to the IRMS, a broader-bore and longer fused-silica capillary was utilized to replace the original sample capillary running from the sample open split to the IRMS. A ẟ¹³C analysis of PAH standards showed accurate ẟ¹³C values, and high precisions (standard deviations 0.13-0.37%) were achieved, with the LOD of HMW-PAHs reduced to at least 1.0 mg/L (i.e., 0.07 to 0.09 nmol carbon per compound on-column). The successful application of this newly developed 2DGC-IRMS scheme provides a practical solution for the reliable CSIA of trace-level pollutants in complex environmental samples that cannot be measured using the conventional GC-IRMS system.

Distribution and source assignments of polycyclic aromatic and aliphatic hydrocarbons in sediments and biota of the Lafayette River, VA

The Lafayette River comprises a tidal sub-estuary constrained by an urban watershed that is bounded by residential areas at its upper reaches and port activity at its mouth. We determined the concentrations and distributions of polycyclic aromatic hydrocarbons (PAHs) and aliphatic n-alkanes across 19 sites from headwaters to river mouth in surface sediments (0-2 cm). Potential atmospheric sources were investigated through the analysis of wet and dry deposition samples and intact coals from a major export terminal nearby. The potential consequences for human consumption were examined through analysis of native oyster (Crassostrea virginica) and blue crab tissues (Callinectes sapidus). A suite of up to 66 parent and alkyl-substituted PAHs were detected in Lafayette sediments with total concentrations ranging from 0.75 to 39.00 µg g^-1 dry wt. Concentrations of aliphatic n-alkanes (n-C₁₆ - n-C₃₁) ranged from 4.94 to 40.83 μg g^-1 dry wt. Source assignment using diagnostic ratios and multivariate source analysis suggests multiple sources contribute to the hydrocarbon signature in this metropolitan system with automotive and atmospheric transport of coal dust as the major contributors. Oyster tissues showed similar trends as PAHs observed in sediments indicating similar sources to water column particles which ultimately accumulate in sediments with crabs showing altered distributions as a consequence of metabolism.

Seasonal variation of temperature affects HMW-PAH accumulation in fishery species by bacterially mediated LMW-PAH degradation

Currently, the specific mechanism generating seasonal variation in polycyclic aromatic hydrocarbons (PAHs) via bacterial biodegradation remains unclear, and whether this alteration affects PAH bioaccumulation is unknown. Therefore, we performed a study between 2015 and 2020 to investigate the effects of seasonal variation on bacterial communities and PAH bioaccumulation in the Pearl River Estuary. Significantly high PAH concentrations in both aquatic and fishery species were determined in dry seasons (the mean ∑₁₆PAH concentration: water, 37.24 ng/L (2015), 30.83 ng/L (2020); fish, 51.01 ng/L (2015) and 72.60 ng/L (2020)) compared to wet seasons (the mean ∑₁₆PAH concentration: water, 22.38 ng/L (2015), 19.40 ng/L(2020); fish, 25.28 ng/L (2015) and 32.59 ng/L (2020)). Distinct differences in taxonomic and functional composition of bacterial communities related to biodegradation of low molecular weight PAHs (LMW-PAHs) were observed between seasons, and the concentrations of PAHs were negatively correlated with seasonal variation in temperature. Temperature-related specific bacterial taxa (e.g., Stenotrophomonas) directly or indirectly participated in LMW-PAH degradation via encoding PAH degradation enzymes (e.g., protocatechuate 4,5-dioxygenase) that subsequently led to bioaccumulation of high molecular weight PAHs (HMW-PAHs) in wild and fishery species due to LMW-PAHs in the water. Based on this alteration, the ecological risk posed by PAHs decreased in wet seasons, and an unbalanced spatio-temporal distribution of PAHs was observed in this estuary. These results suggest that seasonal variation of temperature affects HMW-PAH accumulation in fishery species via bacterially mediated LMW-PAH biodegradation.