PAH distribution and mass fluxes in the Three Gorges Reservoir after impoundment of the Three Gorges Dam

High-density sampling reveals the occurrence, levels and transport flux of 15 polycyclic aromatic hydrocarbons derivatives (PAHs-d) along the Yangtze River

Polycyclic aromatic hydrocarbons derivatives (PAHs-d) have higher toxicity levels compared to its parent polycyclic aromatic hydrocarbons (PPAHs). Their partitioning in different media and large-scale transport patterns in rivers remain largely unknown. This study investigated the occurrence of 15 PAHs-d and 19 PPAHs in water and suspended particulate matter (SPM) of the Yangtze River between 2019 and 2020. The range of Σ15PAHs-d concentrations was 20.54 to 2010.03 ng·L-1 in water and 0.62 to 29.80 μg·g-1 in SPM. The primary PAHs-d components were 2,6-dimethylnaphthalene, 2-methylnaphthalene, and anthraquinone. The range of Σ19PPAHs concentrations in water and SPM was 34.89 to 739.53 ng·L-1 and 0.37 to 204.62 μg·g-1, respectively. And low-ring PAHs-d and PPAHs were more prevalent in water than SPM. Partitioning behaviors indicated that PAHs-d and PPAHs were more readily partitioned into water and SPM during normal and dry periods, respectively. The concentrations of PAHs-d saw significant changes in their spatial distribution, which rose in water and reduced in SPM in downstream of the Three Gorges Dam. This is due to the dam's blocking effect on sediment transport. Positive matrix factorization source analysis revealed biomass combustion upstream and vehicle emissions downstream as primary sources, shaped by the evolving energy consumption patterns of urban areas situated around the Yangtze River. The annual fluxes of PAHs-d in water and SPM of the Yangtze River were 90.40 t·yr-1 and 11.95 t·yr-1, representing 88.3 % and 11.7 % of the overall PAHs-d fluxes, respectively. The total fluxes of PAHs-d and PPAHs in water and SPM tended to increase spatially along the river, with growth rates exceeding 76 and 24 times, respectively. Interception within the Three Gorges Reservoir area has resulted in the differences in the concentration and transport distribution of PAHs-d and PPAHs upstream and downstream, which play important roles in reducing PAHs-d and PPAHs entry into the sea. Future studies on PAHs-d in Yangtze River basin tributaries and estuaries are essential.

Polycyclic Aromatic Hydrocarbons in Topsoils Along the Taipu River Banks in the Yangtze River Delta, China: Occurrence, Source and Risk Assessment

Taipu River is an important transboundary river and drinking water source in the Yangtze River Delta, China. This study collected 15 topsoil samples along the Taipu River banks and subsequently determined the polycyclic aromatic hydrocarbons (PAHs) concentrations, sources, and ecological and health risks. The sum of toxic 15 PAHs concentrations ranged from 83.13 to 28342.53 ng/g, with a mean of 2828.69 ng/g. High molecular weight (HMW) PAHs were the dominant components and Indene (1,2,3, -cd) benzopyrene (InP) accounted for the highest proportion in individuals. The average PAH concentration in residential land was the highest, followed by those in industrial and agricultural land. The PAH concentration was positively related to contents of total carbon, total nitrogen, ammonium nitrogen, and aminopeptidase activity in soils. The mixed combustion of biomass, coal, and petroleum and traffic emissions could be the primary PAH contributors. The total PAHs at over half of sampling points had relatively high risk quotients and incremental lifetime cancer risk (ILCR) values, posing potential or great ecological threats and health risks.

Distribution, sources, and ecological risk assessment of polycyclic aromatic hydrocarbons in agricultural and dumpsite soils in Sierra Leone

This study investigates the concentration and distribution of polycyclic aromatic hydrocarbons (PAHs) in soils, potential sources, risk assessment, and soil physicochemical properties influencing PAH distribution in developed and remote cities in Sierra Leone. Seventeen topsoil samples (0-20 cm) were collected and analyzed for 16 PAHs. The average concentrations of Σ₁₆PAH in soils in the surveyed areas were 1142 ng g^-1 dw, 265 ng g^-1 dw, 79.7 ng g^-1 dw, 54.3 ng g^-1 dw, 54.2 ng g^-1 dw, 52.3 ng g^-1 dw, and 36.6 ng g^-1 dw in Kingtom, Waterloo, Magburaka, Bonganema, Kabala, Sinikoro, and Makeni, respectively. Based on the European soil quality guidelines, Kingtom and Waterloo soils were categorized as heavily and weakly contaminated soil PAHs respectively. The main PAH compounds of this study were 2-ring, 4-ring, and 5-ring PAHs. High molecular weight PAHs (4-6 rings) made up 62.5% of the total PAHs, while low molecular weight PAHs (2-3 rings) was 37.5%. In general, HMWPAHs were predominant in Kingtom, followed by Waterloo. The appointment of PAH sources using different methods revealed mixed sources, but predominantly pyrogenic sources (petroleum, biomass, coal, and fossil fuel contributions). Soil pH has a significant impact on PAH distribution. The toxicity equivalent quantity (TEQ_BaP) levels in soils pose a potential health risk to residents in developed cities but pose a negligible health risk to residents in remote cities. This study is significant as its findings reveal the status of PAH soil contamination in Sierra Leone. The results have important implications for policymakers and stakeholders to identify high-risk zones and establish proper environmental monitoring programs, pollution control measures, and remediation strategies to prevent future risks.

Heavy metal toxicity, ecological risk assessment, and pollution sources in a hydropower reservoir

Heavy metal (HM) toxicity, ecological risk, and pollution sources were analyzed using the pollution indexing and statistical methods in the Three Gorges Reservoir (TGR). The average concentration of HM increased in the order of Cr < Ni < As < Cd < Cu < Mn < Pb < Zn < Al < Fe during the recharge period and Cd < Cr < Ni < As < Cu < Pb < Mn < Zn < Al < Fe during the discharge period. Significant spatial variations of Pb, Zn, Cd, As, Mn, Ni, Cr, and Cu were observed at the upstream and downstream sampling sites. Pb sharply increased during the recharge period, ranges (6.93 -148.62 μg/L) and exceeded WHO and USPEA standards limit. HPI, HEI, Cd, WPI indicated low pollution and moderate pollution with the strong influence of Pb and Cd in the discharge and recharging period, respectively. HTML values are below the permissible toxicity load except for Pb. The Pb toxicity removal percentage is 56.47%, suggesting that the lead's toxicity level is high in TGR and requires the removal process. Ecological risk index values indicated that pollution is low in TGR. The potential ecological risk indexes (RI) of 9.07 and 31.60 were obtained for the discharge and recharge period, respectively, indicating low potential ecological risk from heavy metals in TGR. However, RI values revealed that (Pb, Cd, As Cr Ni, Cu Zn, and Mn) were the most ecological risk HMs in TGR. A significant ecological risk of Pb and Cd distribution was observed across the TGR. Multivariate statistical results found that Pb, Cd, Zn, Mn, Ni, As, Cr, Cu mainly originate from industrial wastewater, mining, metals processing, and agricultural runoff. Fe and Al were mainly from bedrock weathering. Pb, Cd, Zn HMs are a threat to the reservoir ecosystem. This study delivered a current status of HM pollution, toxicity, ecological risk, and pollution sources, indicating a vital insight into HM pollution and water security management in the Three Gorges Reservoir.

Temporal-spatial variations, source apportionment, and ecological risk of trace elements in sediments of water-level-fluctuation zone in the Three Gorges Reservoir, China

The Three Gorges Reservoir (TGR) plays a crucial role in providing electricity for mega-cities across China. However, since the impoundment was completed in 2006, attention to environmental concerns has also been intensive. In order to determine the distribution, sources, and pollution status of trace elements in the water fluctuation zone of the TGR following ten years of repeated "submergence" and "exposure", we systematically collected 16 paired surface sediment samples (n = 32) covering the entire main body of the TGR in March 2018 (following 6 months of submergence) and September 2018 (after 6 months of exposure), and quantitatively analyzed 13 elements (e.g., Mn, Fe, V, Cr, Ni, Cu, Zn, As, Sr, Y, Zr, Ba, and Pb) using X-ray fluorescence spectrophotometry (XRF). The results showed that, except for Sr, concentrations of trace metals following submergence were generally higher than those after exposure due to the less settling of suspended solids at the faster flow velocity during the drawdown period. Assessment using enrichment factors (EFs) and a geo-accumulation index (Igeo) both characterized a relatively serious anthropogenic pollution status of metals in the upper reaches of the TGR with respect to the middle-lower reaches. Source apportionment by positive matrix factorization (PMF) analysis indicated that agricultural activities (24.8 and 24.3%, respectively) and industrial emissions (24.5 and 22.9%, respectively) were the two major sources in these two periods, followed by natural sources, domestic sewage, and ore mining. Ecological risk assessment showed that metalloid arsenic (As) could be the main potential issue of risk to aquatic organisms and human health. A new source-specific risk assessment method (pRI) combined with PMF revealed that agricultural activities could be the major source of potential ecological risk and should be prioritized as the focus of metal/metalloid risk management in the TGR.

Nitrate-assisted biodegradation of polycyclic aromatic hydrocarbons (PAHs) in the water-level-fluctuation zone of the three Gorges Reservoir, China: Insights from in situ microbial interaction analyses and a microcosmic experiment

An increase in polycyclic aromatic hydrocarbon (PAH) pollution poses significant challenges to human and ecosystem health in the Three Gorges Reservoir (TGR) of the Yangtze River. Based on the combination of PAH analysis with qPCR and high-throughput sequencing of bacteria, 32 topsoil samples collected from 16 sites along the TGR were used to investigate the distribution and biodegradation pathways of PAHs in the water-level-fluctuation zone (WLFZ). The results indicated that the concentrations of PAHs were 43.8-228.2 and 30.8-206.3 ng/g soil (dry weight) under the high- and low-water-level (HWL and LWL) conditions, respectively. The PAH concentration in urban areas was higher than that in rural areas. Under both the HWL and LWL conditions, the abundance of the bamA gene, a biomarker of anaerobic PAH biodegradation, was significantly higher than that of the ring-hydroxylating-dioxygenase (RHD) gene, a biomarker of aerobic PAH biodegradation. The abundance of the bamA gene was significantly positively correlated with PAHs (R² = 0.8), and the biodegradation percentage of PAHs incubated anaerobically was greater than that in the aerobically incubated microcosm experiments. These data implicated a key role of the anaerobic pathway in PAH biodegradation. Co-occurrence network analysis suggested that anaerobic Anaerolineaceae, Dechloromonas, Bacteroidetes_vadin HA17 and Geobacter were key participants in the biodegradation of PAHs. The diversity analysis of functional bacteria based on the bamA gene and microcosm experiments further demonstrated that nitrate was the primary electron acceptor for PAH biodegradation. These findings provide a new perspective on the mechanism of PAH biodegradation in the TGR and knowledge that can be used to develop strategies for environmental management.

Spatial-temporal distribution characteristics and health risk assessment of heavy metals in surface water of the Three Gorges Reservoir, China

Heavy metal contamination in surface water of the Three Gorges Reservoir (TGR) is a distinctly important issue for the water security of the Yangtze River Basin in China. Surface water samples of 46 river sections in the main stream and tributaries of the entire TGR area were collected during high and low water level operation periods of 2015 to 2016 to investigate the spatial-temporal distribution characteristics of six heavy metals (As, Cd, Cr, Cu, Pb and Zn) and assess their health risks. Results indicated that average concentrations of heavy metals in the surface water were lower than the threshold values for the first-grade water quality based on the Chinese standard of GB3838-2002 except for Zn. Heavy metals concentrations at high water levels was slightly lower compared with that at the low water levels in the main stream, As, Cd, Cr and Cu exhibited certain inter-annual decline variations in 2015 and 2016. Heavy metals showed distinctly regional variation and mainly distributed in upstream urban sections of the TGR area. The total health risks caused by heavy metals at the low water level periods, most of which exceeded the maximum acceptable risk level recommended by ICRP (5×10^-5 a^-1), were slightly higher than that at the high water level periods. The average annual health risks caused by carcinogenic and non-carcinogenic heavy metals was ranked as Cr > As > Cd > Pb > Cu > Zn, meanwhile this value via drinking water ingestion was 2 to 3 orders of magnitude larger than that of dermal contact. Carcinogenic heavy metals of Cr and As were the main causes of health risk and should be prioritized as the main focus of aquatic environment risk management in the TGR area.

Spatial-temporal distribution and transport flux of polycyclic aromatic hydrocarbons in a large hydropower reservoir of Southeast China: Implication for impoundment impacts

In order to investigate the impacts of dam-related water impoundment on the spatial-temporal variations and transport of anthropogenic organic pollutants, 15 priority polycyclic aromatic hydrocarbons (PAHs) were analyzed in water samples from the Shuikou Reservoir (SKR) of the Minjiang River. The SKR was formed after the construction of the Shuikou Dam, which is the largest hydropower station in Southeast China. The water samples were collected from the backwater zone of the SKR, in both the wet and dry seasons, corresponding to the drainage and impoundment periods of water flow, respectively. The concentrations of the dissolved PAHs in surface water from the wet season (average of 161 ± 97 ng L^-1) were significantly higher (ANOVA, p < 0.01) than those from the dry season (average of 43 ± 21 ng L^-1). PAH concentrations in the SKR decreased from upstream (industrialized cities) to downstream (rural towns or counties), indicating high PAH loads caused by intensive urbanization effects. The high proportions of 3-ring PAHs in the wet season were from local sources via surface runoff; while the elevated proportions of 4- to 6- ring PAHs in the dry season reflected atmospheric deposition emerged of these PAHs and/or volatilization of 3-ring PAHs enhanced. Molecular diagnostic ratios of PAH isomers in multimedium and principal component analysis indicated that PAH presence in the SKR was mainly attributed to pyrogenic origin. The isomeric ratios of fluoranthene to fluoranthene plus pyrene in the wet season were homogeneous, implying that there were continuous new inputs along the riverine runoff. However, these ratios showed spatial downward trend in the dry season, indicating continued degradation of PAHs occurred along the transport path during the impoundment period. The input and output fluxes of PAHs in the SKR were 5330 kg yr^-1 and 2991 kg yr^-1, revealing that the reservoir retained contaminants after impoundment of the hydropower dam.

Prioritizing selected PPCPs on the basis of environmental and toxicogenetic concerns: A toxicity estimation to confirmation approach

Pharmaceuticals and personal care products (PPCPs), the pollutants of emerging concerns, present potential risks to the ecological environment. This study focused on the prioritization of widely used selected PPCPs belonging to two categories:personal care products (PCPs) and non-steroidal anti-inflammatory drugs (NSAIDs). We predicted the toxicogenetic endpoints of PPCPs and then confirmed them using experimental approaches. Our results revealed a significant similarity in the findings obtained through both approaches, indicating NSAIDs with relatively high environmental impacts and in vitro/vivo toxicity. Experimental approach revealed that musk xylene (MX) from PCPs and DIC from NSAIDs as individual chemicals of priority concern showed elevated environmental impacts and significantly induced pi3k-akt-mTOR in vitro. Similarly, propyl paraben (PP) from PCPs and diclofenac (DIC) from NSAIDs caused significant cytotoxicity and DNA damage in vitro. Moreover, PP and MX from the PCPs group and naproxen (NAP) and DIC from the NSAIDs group induced developmental toxicity and perturbations to phases I, II, and III detoxification pathways in vivo. In addition, MX and DIC as priority PPCPs inhibited hematopoiesis and hepatogenesis in vivo. Apart from the specific effects, PPCPs can be ranked as: MX > PP > methylparaben (MP) for PCPs, and DIC > NAP > ibuprofen (IBU) for NSAIDs, regarding their toxic and environmental concerns.

Effects of water impoundment and water-level manipulation on the bioaccumulation pattern, trophic transfer and health risk of heavy metals in the food web of Three Gorges Reservoir (China)

The Three Gorges Reservoir (TGR) of China, the largest hydropower project over the world, has attracted much attention to the water impoundment and water-level manipulation. In this study, we evaluated potential effects of water impoundment and seasonal water-level manipulation on the bioaccumulation, trophic transfer and health risk of HMs (Cu, Fe, Zn, Hg, Cd and Pb) in food web components (seston, aquatic invertebrate and fish) in TGR. Our results show that, after the impoundment for eight years (2003-2010), all of the six metal concentrations in aquatic biota fell within the criteria of safety quality guidelines. The concentrations of Cu, Fe, Zn and Hg in fish and aquatic invertebrates were higher than those before impoundment, whereas Cd and Pb were lower than those before impoundment. Nonetheless, Hg, Cd and Pb in aquatic consumers underwent an increasing trend during the entire impoundment, implying potential reservoir effect in the future. Only the concentrations of Hg, Cd and Pb in aquatic consumers exhibited a declining trend towards the dam, showing consistent with the background level at the three reaches. Seasonal variations in HM concentrations of fish and aquatic invertebrates were ascribed to the water-level manipulation associated with reservoir management. Our findings show that Hg or Cd biomagnified through aquatic food web during different hydrological periods, whereas Pb, Cu, Fe and Zn exhibited weak biomagnification power. Overall, Hg, Cd and Pb showed a higher risk than that of Cu, Fe and Zn.

Distribution and sources of polycyclic aromatic hydrocarbons and phthalic acid esters in water and surface sediment from the Three Gorges Reservoir

After the impoundment of the Three Gorges Reservoir (TGR), the hydrological situation of the reservoir has changed greatly. The concentration and distribution of typical persistent organic pollutants in water and sediment have also changed accordingly. In this study, the concentration, distribution and potential sources of 16 polycyclic aromatic hydrocarbons (PAHs) and 6 phthalic acid esters (PAEs) during the water drawdown and impoundment periods were investigated in water and sediment from the TGR. According to our results, PAHs and PAEs showed temporal and spatial variations. The mean ΣPAH and ΣPAE concentrations in water and sediment were both higher during the water impoundment period than during the water drawdown period. The water samples from the main stream showed larger ΣPAH concentration fluctuations than those from tributaries. Both the PAH and PAE concentrations meet the Chinese national water environmental quality standard (GB 3838-2002). PAH monomers with 2-3 rings and 4 rings were dominant in water, and 4-ring and 5-6-ring PAHs were dominant in sediment. Di-n-butyl phthalate (DBP) and di-2-ethylhexyl phthalate (DEHP) were the dominant PAE pollutants in the TGR. DBP and DEHP had the highest concentrations in water and sediment, respectively. The main source of PAHs in water from the TGR was petroleum and emissions from coal and biomass combustion, whereas the main sources of PAHs in sediments included coal and biomass combustion, petroleum, and petroleum combustion. The main source of PAEs in water was domestic waste, and the plastics and heavy chemical industries were the main sources of PAEs in sediment.

Adapting current model with field data of related performance reference compounds in passive samplers to accurately monitor hydrophobic organic compounds in aqueous media

Performance reference compounds (PRCs) are neutral organic compounds, introduced in a passive sampler prior deployment for the assessment of in situ sampling rate. In this study, evaluation of in situ sampling rates of 16 ¹³C-PAH-PRCs with moderate and high hydrophobicity was established to provide an overall correction factor for variations in virtual organism (VO) uptake rates of the analytes of interest. In situ sampling rate was compared to an empirical model during sampling campaign in 2011 with VO in 12 different sites along the Three Gorges Reservoir (TGR) in China. A discrepancy was observed for high hydrophobic compounds with log K _ow ranging from 5.18 to 6.63 where ΣPAH concentration in TGR from Huckins model (305,624 pg/L) was resulted to be roughly 2-fold higher than the alternative procedure (182,292 pg/L). A relationship between in situ sampling rates of the 16 ¹³C-PAH-PRCs (Rs, _PRC ) and log K _ow was set up to allow then calculation of analyte sampling rate Rs _analyte (N) of various organic pollutants with log K _ow  ≤ 6.63.

Characterization of heavy metal contamination in the soil and sediment of the Three Gorges Reservoir, China

This paper analyzes the concentration, distribution, bioavailability, and potential heavy metal contamination risk of Cu, Pb, Cd, Zn, and Cr in the soil and sediment of the Three Gorges Reservoir (TGR). In this paper, 14 stations that cover the upper reaches to the lower reaches of the TGR were selected. The spatial distribution of heavy metals in the TGR showed that the average concentrations of Cu, Pb, Cd, Zn, and Cr were higher in the upper and lower reaches than those in the middle reaches because of industrial and agricultural activities as well as natural processes (e.g., soil erosion, rock weathering). The results also indicated that multiple pollution sources and complex geomorphological, geochemical and biological processes resulted in remarkably higher heavy metal concentrations in the soils of the water-level-fluctuation zone (WLFZ) than in the soils of the banks. The Cu, Pb, Cd, Zn, and Cr concentrations in the soils of the TGR did not exceed their respective maximum allowable concentration (MAC) values for agricultural soils in China, indicating that the soil in the TGR was not seriously contaminated with Cu, Pb, Cd, Zn, or Cr. However, the mean concentrations of all the studied metals in the sediments were higher than the geochemical background values and much higher than those in the soils, thus indicating the effect of the pollution sources and the altered hydrologic conditions that occurred after the impoundment of the TGR. A geoaccumulation index analysis indicated that the TGR sediments were moderately polluted with Cu and Cd, unpolluted to moderately polluted with Pb and Cr, and unpolluted with Zn. Fractionation studies indicated that Cd was mainly present in the non-residual fractions and exhibited great instability and bioavailability; furthermore, the alternating wetting and drying of the WFLZ soils enhance the mobility and bioavailability of Cd. Thus, greater attention should be paid to Cd pollution in the TGR because of its higher risk assessment values and potentially adverse biological effects.

Diverse toxicological risks of PAHs in surface water with an impounding level of 175m in the Three Gorges Reservoir Area, China

The impounding level of 175m for the Three Gorges Reservoir (TGR) is of vital importance for efficient flood control, power generation and convenient navigation in China. However, little is known about the spatial distribution and toxicological risks of major pollutants in the Three Gorges Reservoir Area (TGRA) at that stage. The aim of this study is to probe the ubiquitous polycyclic aromatic hydrocarbons (PAHs) contamination and toxicological impacts in the surface water of the TGRA at the highest water impoundment level of 175m. Our results showed that the ƩPAHs levels ranged from 83 to 1631ng/L in the upper reaches, 354 to 1159ng/L in the middle reaches, and 23 to 747ng/L in the lower reaches of the TGRA. Source apportionment of PAHs indicated that coal combustion, industrial emissions, heavy traffic, agriculture and shipping activities were the primary sources. Compositional pattern highlighted >85% dominancy of low molecular weight (LMW) PAHs in the reservoir. Risk assessment based on risk quotients (RQs) implied moderate to high ecological risks: the upper reaches>the middle reaches>the lower reaches. However, gene expression profiles portrayed contrary scenario because of the presence of relatively higher footprints of high molecular weight (HMW) PAHs in the middle and the lower reaches, which was confirmed by Cox hazard proportional model. Moreover, the transgenic zebrafish Tg(cyp1a:gfp) induced by PAHs also expressed stronger fluorescent signals in the middle and lower reaches. Taken together, different approaches were employed to firstly reveal the real status of ecological toxicity of PAHs and explore the underlying mechanisms at the highest impounding level of 175m in the TGRA.

Distribution, sources, and ecological risk assessment of polycyclic aromatic hydrocarbons in the water and suspended sediments from the middle and lower reaches of the Yangtze River, China

Samples were collected from the middle and lower reaches of the Yangtze River, China, to study the concentrations, distributions, and compositions of 16 US-EPA priority polycyclic aromatic hydrocarbons (PAHs) in water and suspended particulate matter (SPM). We also evaluated sources of the PAHs and their potential toxicity. Total concentrations of the PAHs (ΣPAHs) in water ranged from 17.33 to 77.12 ng L(-1), and in SPM, the levels ranged from 595.91 to 2473.74 ng g(-1). Total concentrations of seven carcinogenic PAHs (ΣCPAHs) ranged from 7.63 to 13.02 ng L(-1) in water and 276.55 to 1216.89 ng g(-1) in SPM. PAH levels in water samples were relatively low, and those in the lower reaches were higher than in the middle reaches. SPM samples had higher levels of PAHs, especially in the lower reaches and in Dongting Lake and Poyang Lake. Principal component analysis (PCA) with multiple linear regression analysis (MLR) was performed to quantitatively characterize the PAH sources. Two factors and their contributions were identified from water samples. Coal and wood combustion accounted for 74.1 % of the PAHs, and petroleum emissions explained 25.9 % of the PAHs. Three source factors were identified from SPM samples: these were vehicular emissions (46.3 % of PAHs), wood and coal combustion (40.4 % of PAHs), and petrogenic sources (13.3 %). Ecological risk assessment indicated that a moderate undesirable impact will be caused by PAHs, and some control measures and remedial actions should be conducted.

Linking Ah receptor mediated effects of sediments and impacts on fish to key pollutants in the Yangtze Three Gorges Reservoir, China - A comprehensive perspective

The Three Gorges Reservoir (TGR), created in consequence of the Yangtze River's impoundment by the Three Gorges Dam, faces numerous anthropogenic impacts that challenge its unique ecosystem. Organic pollutants, particularly aryl hydrocarbon receptor (AhR) agonists, have been widely detected in the Yangtze River, but only little research was yet done on AhR-mediated activities. Hence, in order to assess effects of organic pollution, with particular focus on AhR-mediated activities, several sites in the TGR area were examined applying the "triad approach". It combines chemical analysis, in vitro, in vivo and in situ investigations to a holistic assessment. Sediments and the benthic fish species Pelteobagrus vachellii were sampled in 2011/2012, respectively, to identify relevant endpoints. Sediment was tested in vitro with the ethoxyresorufin-O-deethylase (EROD) induction assay, and in vivo with the Fish Embryo Toxicity Test and Sediment Contact Assay with Danio rerio. Activities of phase I (EROD) and phase II (glutathione-S-transferase) biotransformation enzymes, pollutant metabolites and histopathological alterations were studied in situ in P. vachellii. EROD induction was tested in vitro and in situ to evaluate possible relationships. Two sites, near Chongqing and Kaixian city, were identified as regional hot-spots and further investigated in 2013. The sediments induced in the in vitro/in vivo bioassays AhR-mediated activities and embryotoxic/teratogenic effects - particularly on the cardiovascular system. These endpoints could be significantly correlated to each other and respective chemical data. However, particle-bound pollutants showed only low bioavailability. The in situ investigations suggested a rather poor condition of P. vachellii, with histopathological alterations in liver and excretory kidney. Fish from Chongqing city exhibited significant hepatic EROD induction and obvious parasitic infestations. The polycyclic aromatic hydrocarbon (PAH) metabolite 1-hydroxypyrene was detected in bile of fish from all sites. All endpoints in combination with the chemical data suggest a pivotal role of PAHs in the observed ecotoxicological impacts.

Yangtze Three Gorges Reservoir, China: A holistic assessment of organic pollution, mutagenic effects of sediments and genotoxic impacts on fish

Besides obvious benefits, the Three Gorges Dam's construction resulted in new pollution scenarios with the potentials to threaten the Three Gorges Reservoir (TGR) ecosystem. In order to record organic contamination, to find links to ecotoxicological impacts and to serve as reference for ensuing monitoring, several sites in the TGR area were screened applying the triad approach with additional lines-of-evidence as a holistic assessment method. Sediments and the benthic fish species Pelteobagrus vachellii were sampled in 2011 and 2012 to determine organic pollution levels, mutagenic potentials and genotoxic impacts. Two regional hot-spots near the cities of Chongqing and Kaixian were identified and further investigated in 2013. Only polycyclic aromatic hydrocarbons (PAHs) could be detected in sediments in 2011 (165-1653ng/g), emphasizing their roles as key pollutants of the area. Their ubiquity was confirmed at Chongqing (150-433ng/g) and Kaixian (127-590ng/g) in 2013. Concentrations were comparable to other major Chinese and German rivers. However, the immense sediment influx suggested a deposition of 216-636kgPAH/day (0.2-0.6mgPAH/(m(2)·day)), indicating an ecotoxicological risk. PAH source analysis highlighted primary impacts of combustion sources on the more industrialized upper TGR section, whereas petrogenic sources dominated the mid-low section. Furthermore, sediment extracts from several sites exhibited significant activities of frameshift promutagens in the Ames fluctuation assay. Additionally, significant genotoxic impairments in erythrocytes of P. vachellii were detected (Chongqing/Kaixian), demonstrating the relevance of genotoxicity as an important mode of action in the TGR's fish. PAHs, their derivatives and non-target compounds are considered as main causative agents.

Integrated targeted and non-targeted analysis of water sample extracts with micro-scale UHPLC-MS

A sensitive method is introduced to detect selected pharmaceutical residues and polar pesticides with UHPLC–MS in water samples of different origin. Active or passive water sampling was combined with a laboratory solid-phase extraction cleanup and stable isotope dilution analysis. Recovery experiments demonstrated that the internal standard correction performed well for the compensation of matrix effects. Besides, the original targeted analysis approach was expanded by non-target analysis of the samples with only one more consecutive injection run needed. The key benefits of this multi-residue analysis are:•

Targeted analysis and quantification combined with non-target analysis on a micro-scale UHPLC–MS system usually employed for qualitative analysis only.

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The internal standards for targeted analysis were used in non-target runs to calculate the partition coefficient log P of unknown substances employing the retention time index (RTI).

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The filtering of database hits for two criteria (exact mass and partition coefficient) significantly reduced the list of suspects and at the same time rendered it possible to perform non-target analysis with lower mass accuracy (no lock-spray) in the range of 20–500 ppm.

Response of PAH-degrading genes to PAH bioavailability in the overlying water, suspended sediment, and deposited sediment of the Yangtze River

The degrading genes of hydrophobic organic compounds (HOCs) serve as indicators of in situ HOC degradation potential, and the existing forms and bioavailability of HOCs might influence the distribution of HOC-degrading genes in natural waters. However, little research has been conducted to study the relationship between them. In the present study, nahAc and nidA genes, which act as biomarkers for naphthalene- and pyrene-degrading bacteria, were selected as model genotypes to investigate the response of polycyclic aromatic hydrocarbon (PAH)-degrading genes to PAH bioavailability in the overlying water, suspended sediment (SPS), and deposited sediment of the Yangtze River. The freely dissolved concentration, typically used to reflect HOC bioavailability, and total dissolved, as well as sorbed concentrations of PAHs were determined. Phylogenetic analysis showed that all the PAH-ring hydroxylating dioxygenase gene sequences of Gram-negative bacteria (PAH-RHD[GN]) were closely related to nahAc, nagAc, nidA, and uncultured PAH-RHD genes. The PAH-RHD[GN] gene diversity as well as nahAc and nidA gene copy numbers decreased in the following order: deposited sediment>SPS>overlying water. The nahAc and nidA gene abundance was not significantly correlated with environmental parameters but was significantly correlated with the bioavailable existing forms of naphthalene and pyrene in the three phases. The nahAc gene copy numbers in the overlying water and deposited sediment were positively correlated with freely dissolved naphthalene concentrations in the overlying and pore water phases, respectively, and so were nidA gene copy numbers. This study suggests that the distribution and abundance of HOC-degrading bacterial population depend on the HOC bioavailability in aquatic environments.