Dioxin-like activity in sediments from Tai Lake, China determined by use of the H4IIE-luc bioassay and quantification of individual AhR agonists

Instrumental and bioanalytical characterization of dioxin-like activity in sediments from the Yeongsan River and the Nakdong River estuaries, South Korea

In the present study, we investigated the contamination status of dioxin-like chemicals (DLCs) and potential toxic effects associated with river and coastal sediments from two large estuaries of South Korea. Sediments collected from the Yeongsan River and the Nakdong River estuaries were analyzed for several DLCs, including polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs), coplanar polychlorinated biphenyls (co-PCBs), and polycyclic aromatic hydrocarbons (PAHs). Greater concentrations of target DLCs (except for PCDDs in Nakdong River) were found in the inland creeks with decreasing trends towards estuarine and coastal areas in both regions. The result indicated that the elevated DLCs were attributable to the surrounding land use activities, such as point sources of industrial and municipal areas from the inland regions. Principal component analysis and positive matrix factorization model revealed that major sources of PCDD/Fs and PAHs in sediments were fly ash and dust, and petroleum and diesel emission, respectively. The dioxin-like activities of the sediments ranged from 0.98 to 88% of the maximal induction elicited by 2,3,7,8-tetrachlorodibenzo-p-dioxin, which generally explained the sedimentary contamination by the target DLCs. Dioxin-like activity in sediments from the artificial lake and inland creek of the Nakdong River Estuary was mostly explained by the targeted DLCs (~75%). However, the contribution of known DLCs from the sediments of the Yeongsan River Estuary was relatively low (~35%) compared to that of the Nakdong River Estuary, suggesting the presence of unknown DLCs in sediments. Overall, the distribution of DLCs quite varied by region, generally reflecting the difference in the surrounding land use activity. In the future, it is needed to study the distribution, sources, and potential ecological effects of unknown toxic substances in coastal sediments.

Oxidative stress and EROD activity in Caco-2 cells upon exposure to chlorinated hydrophobic organic compounds from drinking water reservoirs

Our previous studies showed hydrophobic organic compounds (HOCs) in the sediments of drinking water reservoirs caused DNA damage in human cells (Caco-2) after chlorination. However, the main mechanisms remained unclear. This study compared oxidative damage and EROD activity in Caco-2 cells upon exposure to chlorinated HOCs, and the role of antioxidants (catalase, vitamin C and epigallocatechin gallate (EGCG)) in reducing the toxicities was examined. The result showed that chlorinated HOCs induced a 4-fold increase in production of reactive oxygen species (ROS) compared with HOCs. Antioxidants supplement significantly reduced ROS yields and DNA peroxidation. HOCs with relatively higher TEQ_bio were greatly reduced (about 98%) after chlorination, indicating dioxin-like toxicity is not the main factor inducing oxidative damage by chlorinated HOCs. Yet, ROS and the associated oxidative damage seem to be more responsible for causing DNA damage in the cells. Antioxidants including catalase, Vitamin C and EGCG showed protective effect against chlorination.

Detoxification of municipal solid waste incinerator (MSWI) fly ash by single-mode microwave (MW) irradiation: Addition of urea on the degradation of Dioxin and mechanism

The detoxification of municipal solid waste incinerator (MSWI) fly ash dioxins urgently requires an effective treatment technology. In this study, we adopted a single-mode microwave (MW)-based pyrolysis to treat MSWI fly ash under N₂ atmosphere and further elucidated the main influencing factors, including the chemical inhibitor, for dioxin control. The results show that (1) the detoxification process was optimized with a mass ratio of fly ash to SiC of 1:9, 23.1% (wt%) urea addition and pyrolysis temperature of ˜ 480 °C; (2) the total polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) destruction efficiency and the bioassay-derived 2,3,7,8-TCDD toxic equivalent (Bio-TEQ) removal efficiency reached 98.5% and 97.9%, respectively, accompanied with ˜ 1.3% of the total amount of dioxin being submitted to exhaust gas; (3) the MW-based pyrolysis of urea (133˜300 °C) was favourable for the generation of hot spots as well as the PCDD/F rapid destruction in fly ash. In addition, the leaching toxicity of heavy metals was also partially reduced after MW pyrolysis reactions. To the best of our knowledge, this is the first report adopting a MW-based pyrolysis to eliminate dioxin in MSWI fly ash with the addition of urea, which is a promising alternative to current methods.

Biological toxicity estimates show involvement of a wider range of toxic compounds in sediments from Durban, South Africa than indicated from instrumental analyses

The toxic equivalences (TEQs) of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) from sediment of aquatic systems in Durban, South Africa were determined in two ways: 1) TEQs of PAHs and PCBs were determined by instrumental analyses and converted to 2,3,7,8‑tetrachlorodibenzo‑para‑dioxin equivalence (TCDDeq). 2) Bioassay equivalences (BEQs) of aryl hydrocarbon receptor (AhR) ligands were analysed using the H4IIE-luc bioassay. TEQs of PCBs ranged from below limit of detection (<LOD) to 57 pg TCDDeq·g^-1 while PAHs ranged from <LOD to 790 pg TCDDeq·g^-1. BEQs were 100- to 1000-fold greater than TEQs. Potency-balance revealed <10% of the BEQs were explained by instrumentally analysed compounds. Sediment quality guidelines indicated di minimis risk relating to TEQs, however had potential risk due to BEQs. The results reveal that far more AhR ligands were present in the sediments than what was instrumentally analysed and capable of causing AhR-mediated toxicity.

In situ microbiota distinguished primary anthropogenic stressor in freshwater sediments

Conventional assessment and evaluation of sediment quality are based on laboratory-based ecotoxicological and chemical measurements with lack of concern for ecological relevance. Microbiotas in sediment are responsive to pollutants and can be used as alternative ecological indicators of sediment pollutants; however, the linkage between the microbial ecology and ecotoxicological endpoints in response to sediment contamination has been poorly evaluated. Here, in situ microbiotas from the Three Gorges Reservoir (TGR) area of the Yangtze River were characterized by DNA metabarcoding approaches, and then, changes of in situ microbiotas were compared with the ecotoxicological endpoint, aryl hydrocarbon receptor (AhR) mediated activity, and level of polycyclic aromatic hydrocarbons (PAHs) in sediments. PAHs and organic pollutant mixtures mediating AhR activity had different effects on the structures of microbiotas. Specifically, Shannon indices of protistan communities were negatively correlated with the levels of AhR mediated activity and PAHs. The sediment AhR activity was positively correlated with the relative abundance of prokaryotic Acetobacteraceae, but had a negative correlation with protistan Oxytrichidae. Furthermore, a quantitative classification model was built to predict the level of AhR activity based on the relative abundances of Acetobacteraceae and Oxytrichidae. These results suggested that in situ Protista communities could provide a useful tool for monitoring and assessing ecological stressors. The observed responses of microbial community provided supplementary evidence to support that the AhR-active pollutants, such as PAHs, were the primary stressors of the aquatic community in TGR area.

A sensitive, rapid, and simple DR-EcoScreen bioassay for the determination of PCDD/Fs and dioxin-like PCBs in environmental and food samples

In developing countries in Asia, such as China, Vietnam, and Thailand, there is a strong need for the development of relatively rapid and low-cost bioassays for the determination of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and dioxin-like polychlorinated biphenyls (DL-PCBs) in environmental and food samples. These compounds are known to induce a variety of toxic and biological effects through their ligand-specific binding of the aryl hydrocarbon receptor (AhR). Indeed, several AhR-mediated reporter gene assays are widely used as prescreening tools for high-resolution gas chromatography/high-resolution mass spectrometry (HRGC-HRMS) analysis, which individually measures 17 PCDD/Fs and 12 DL-PCBs. In 2008, we have developed a new sensitive and rapid reporter gene assay using a genetically engineered stable cell line, designated DR-EcoScreen cells. The DR-EcoScreen assay using these cells has a number of great advantages of its sensitivity to 2,3,7,8-tetrachlorodibenzo-p-dioxin and its simple procedure, which shows little variance in the data (within CV 10 %) compared to other reporter gene assays. In this review, we summarize the application of the DR-EcoScreen assay to the determination of PCDD/Fs and DL-PCBs in ambient air samples, in fish and shellfish samples, and in flue gas samples from incinerators and provide potential usefulness of this bioassay for the determination of PCDD/Fs and DL-PCBs in various matrices.

Toxicological and chemical insights into representative source and drinking water in eastern China

Drinking water safety is continuously threatened by the emergence of numerous toxic organic pollutants (TOPs) in environmental waters. In this study, an approach integrating in vitro bioassays and chemical analyses was performed to explore toxicological profiles of representative source and drinking water from waterworks of the Yangtze River (Yz), Taihu Lake (Th), and the Huaihe River (Hh) basins in eastern China. Overall, 34 of 96 TOPs were detected in all water samples, with higher concentrations in both source and drinking water samples of Hh, and pollutant profiles also differed across different river basins. Non-specific bioassays indicated that source water samples of Hh waterworks showed higher genotoxicity and mutagenicity than samples of Yz and Th. An EROD assay demonstrated dioxin-like toxicity which was detected in 5 of 7 source water samples, with toxin concentration levels ranging from 62.40 to 115.51 picograms TCDD equivalents per liter of water (eq./L). PAHs and PCBs were not the main contributors to observed dioxin-like toxicity in detected samples. All source water samples induced estrogenic activities of 8.00-129.00 nanograms 17β-estradiol eq./L, and estrogens, including 17α-ethinylestradiol and estriol, contributed 40.38-84.15% of the observed activities in examined samples. While drinking water treatments efficiently removed TOPs and their toxic effects, and estrogenic activity was still observed in drinking water samples of Hh. Altogether, this study indicated that the representative source water in eastern China, especially that found in Hh, may negatively affect human health, a finding that demonstrates an urgent requirement for advanced drinking water treatments.

Evaluation of AhR-agonists and AhR-agonist activity in sediments of Liaohe River protected areas, China

A total of 9 sediment samples of Liaohe River protected areas were collected to evaluate aryl hydrocarbon receptor agonists (AhR-agonists) and AhR-agonist activity via chemical analysis and in vitro H4IIE cell bioassay. Results indicated that bioassay-derived 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalents (Bio-TEQs) ranged from 89.1 to 251.1pg/g dry weight. Concentrations of 16 EPA polycyclic aromatic hydrocarbons (PAHs), 12 dioxin-like polychlorinated biphenyls (PCBs), and polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) ranged from 256.8 to 560.1ng/g, 79.2 to 416.2pg/g, and 199.6 to 538.4pg/g, respectively. According to potency balance analysis, TEQ_chems based on PAHs, PCBs, and PCDD/Fs could contribute 16.56% to 26.11% of Bio-TEQs. This could be explained by the potential existence of unidentified AhR-agonists and the potential non-additive interactions among AhR-agonists in sediment extracts. Through the different contributions to Bio-TEQs, this study confirms that PCDD/Fs were the main pollutants that induced significantly AhR-agonist activity in sediments of Liaohe River protected areas.

Bioavailability-based assessment of aryl hydrocarbon receptor-mediated activity in Lake Tai Basin from Eastern China

Coupling polydimethylsiloxane (PDMS)-based equilibrium passive sampling with chemical and bioassay analysis, we assessed aryl hydrocarbon receptor (AhR)-mediated activity and contributing chemicals in sediment from Lake Tai Basin, Eastern China. The bioanalytical equivalent concentrations (BEQs) of AhR-active chemicals for the exhaustive (total burden) and PDMS extracts (bioavailable fractions) ranged from <9.5-300 ng TCDD-EQ/ kgdry weight (dw) and <0.096-2.2 ng TCDD-EQ/kgdw, respectively, which were of average levels compared to those reported elsewhere. The total concentrations of PAHs in sediment and PDMS were 17-4700 μg/kgdw and 0.61-10 μg/kgdw, respectively. The majority of the exhaustive extracts subject to acid treatment showed >70% decline in AhR-mediated activity, suggesting the minor contribution by persistent AhR ligands. Targeted analysis of polycyclic aromatic hydrocarbons (PAHs) showed, however, that these chemicals contributed <40% to the overall effect in both exhaustive and PDMS extracts, indicating the presence of other labile AhR ligands. The concentrations of PAHs and BEQs of the AhR-mediated activity attributed to these chemicals in the exhaustive extracts can be back calculated from those in the PDMS extracts via a general organic carbon-PDMS partition coefficient. Similar quantitative conversion between PDMS and aquatic organisms was also verified for aquatic organisms via the lipid-PDMS partition coefficient. Therefore, our study provided a first insight into the quantitative links between bulk chemical burdens in sediment, chemical bioavailability, bioaccumulation potential and resulting mixture effects, as an integral part of predictive environmental risk assessment of contaminated sediment.

AhR-mediated activities and compounds in sediments of Meiliang Bay, Taihu Lake, China determined by in vitro bioassay and instrumental analysis

Greater concentrations of TCDD-EQs and lesser concentrations of TEQs were found and a gradual decrease of AhR potency was confirmed.

Evaluation of the ecotoxicity of sediments from Yangtze river estuary and contribution of priority PAHs to ah receptor--mediated activities

In this study, in vitro bioassays were performed to assess the ecotoxicological potential of sediments from Yangtze River estuary. The cytotoxicity and aryl hydrocarbon receptor (AhR)-mediated toxicity of sediment extracts with rainbow trout (Oncorhynchus mykiss) liver cells were determined by neutral red retention and 7-ethoxyresorufin-O-deethylase assays. The cytotoxicity and AhR-mediated activity of sediments from the Yangtze River estuary ranged from low level to moderate level compared with the ecotoxicity of sediments from other river systems. However, Yangtze River releases approximately 14 times greater water discharge compared with Rhine, a major river in Europe. Thus, the absolute pollution mass transfer of Yangtze River may be detrimental to the environmental quality of estuary and East China Sea. Effect-directed analysis was applied to identify substances causing high dioxin-like activities. To identify unknown substances contributing to dioxin-like potencies of whole extracts, we fractionated crude extracts by open column chromatography. Non-polar paraffinic components (F1), weakly and moderately polar components (F2), and highly polar substances (F3) were separated from each crude extract of sediments. F2 showed the highest dioxin-like activities. Based on the results of mass balance calculation of chemical toxic equivalent concentrations (TEQs), our conclusion is that priority polycyclic aromatic hydrocarbons indicated a low portion of bio-TEQs ranging from 1% to 10% of crude extracts. Further studies should be conducted to identify unknown pollutants.