Derivation of predicted no-effect concentration and ecological risk for atrazine better based on reproductive fitness

Concentration levels and ecological risk assessment of typical organophosphate esters in representative surface waters of a megacity

Organophosphate esters (OPEs) have been widely used as flame retardants and plasticizers in consumer and industrial products. They have been found to have numerous exposure hazards. Recently, several OPEs have been detected in surface waters around the world, which may pose potential ecological risks to freshwater organisms. In this study, the concentration, spatial variation, and ecological risk of 15 OPEs in the Beiyun and Yongding rivers were unprecedentedly investigated by the ultra-performance liquid chromatography-tandem mass spectrometry (UPLC-MS/MS) and risk quotient (RQ) method. The result showed that triethyl phosphate (TEP), tri (2-chloroisopropyl) phosphate (TCPP) were the most abundant OPEs with average concentrations of 55.53 ng/L and 42.29 ng/L, respectively. The concentrations of OPEs in the Beiyun River are higher than in the Yongding River, and their levels were higher in densely populated and industrial areas. The risk assessment showed that there was insignificant from OPEs to freshwater organisms in these rivers (RQs <0.1). The risk was higher downstream than upstream, which was related to human-intensive industrial activities downstream in the Yongding River. The ecological risk of OPEs in surface waters worldwide was estimated by joint probability curves (JPCs), and the result showed that there was a moderate risk for tri (2-chloroethyl) phosphate (TCEP), a low risk for trimethyl phosphate (TMP), and insignificant for other OPEs. In addition, the QSAR-ICE-SSD model was used to calculate the hazardous concentration for 5% (HC5). This result validated the feasibility and accuracy of this model in predicting acute data of OPEs and reducing biological experiments on the toxicity of OPEs. These results revealed the ecological risk of OPEs and provided the scientific basis for environmental managers.

Non-target screening and prioritization of organic contaminants in seawater desalination and their ecological risk assessment

The impact of desalination brine on the marine environment is a global concern. Regarding this, salinity is generally accepted as the major environmental factor in desalination concentrate. However, recent studies have shown that the influence of organic contaminants in brine cannot be ignored. Therefore, a non-targeted screening method based on comprehensive two-dimensional gas chromatography-quadrupole mass spectrometry (GC × GC-qMS) was developed for identifying organic contaminants in the desalination brine. A total of 404 compounds were tentatively identified from four seawater desalination plants (three reverse osmosis plants and one multiple effect distillation plant) in China. The identified compounds were prioritized based on their persistence, bioaccumulation, ecotoxicity, usage, and detection frequency. Twenty-one (21) compounds (seven phthalates, ten pesticides, four trihalomethanes) were then selected for further quantitative analysis and ecological risk assessment, including compounds from the priority list along with substances from the same chemical classes. Ecologically risky substances in brine include diisobutylphthalate and bis(2-Ethylhexyl) phthalate, atrazine and acetochlor, and bromoform. Most of the contaminants come from raw seawater, and no high risk contaminants introduced by the desalination process have been found except for disinfection by-products. In brine discharge management, people believed that all pollution in raw seawater was concentrated by desalination process. This study shows that not all pollutants are concentrated during the desalination process. In this study, the total concentration of pesticide in the brine increased by 58.42%. The concentration of ∑PAEs decreased by 13.65% in reverse osmosis desalination plants and increased by 10.96% in the multi-effect distillation plant. The concentration of trihalomethane increased significantly in the desalination concentrate. The change in the concentration of pollutants in the desalination concentrate was related to the pretreatment method and the chemical characteristics of the contaminants. The method and results given in this study hinted a new idea to identify and control the environmental impact factors of brine.

Analyzing species sensitivity distribution of evidently edible microplastics for freshwater biota

Assessing the ecological risks of microplastics is difficult because of the limited availability of reliable ecotoxicity data. Although freshwater is a valuable sink for microplastics, the current framework for ecological risk assessment using traditional toxicity data is not applicable to freshwater ecosystems. Herein, species sensitivity distribution (SSD) curves were compared for edible and all microplastics exposed to aquatic organisms based on traditional endpoint-based and all-endpoint-based databases. Freshwater toxicity data for microplastics were screened after verifying microplastic presence in test species (56 toxicity datapoints for one microalga, three water fleas, one fish, and one crab; 0.02-100 µm-sized microplastics). SSD and curve parameters were compared with or without non-traditional toxicity endpoints. The HC50 in all endpoint databases was more sensitive than that in the traditional endpoint database and showed a good fit. SSD curves derived from the database for all microplastics were compared and analyzed with edible microplastics. HCx increased for edible microplastics (0.02-100 µm-sized) than for all microplastics (0.02-200 µm-sized), and the size of edible microplastics was lower than of all microplastics. Thus, using non-traditional toxicity data, the SSD approach compensates for the limited ecotoxicity data on microplastics while considering the internalization of microplastics in biota.

Aquatic ecological risk assessment of imidacloprid and thiacloprid in an urban river of Qingdao, China

Imidacloprid and thiacloprid, two neonicotinoid insecticides that are extensively used in urban areas, are potentially toxic to non-target aquatic organisms. In this study, the concentrations of imidacloprid and thiacloprid in surface runoff after rainfall were 20.79-43.77 ng/L and 25.13-63.84 ng/L, respectively, whereas the levels for the Licun River were 10.78-41.70 ng/L and 2.66-39.68 ng/L, respectively. The acute and chronic criteria for imidacloprid and thiacloprid are 0.865, 0.006, 0.83, and 0.012 μg/L, respectively. Tiered ecological risk assessments revealed the chronic ecological risks of these micropollutants to local aquatic species. There was a moderate chronic toxicity risk associated with imidacloprid and thiacloprid in the Licun River, and the joint probability curves showed a probability of chronic ecological risk to 5 % of the aquatic organisms at 68 %-97 %. The results provide evidence of urban surface runoff transporting micropollutants from surface into rivers and estuaries, highlighting the ecological risks to aquatic ecosystems.

Deriving aquatic PNECs of endocrine disruption effects for PFOS and PFOA by combining species sensitivity weighted distributions and adverse outcome pathway networks

Perfluorooctanesulfonic acid (PFOS) and perfluorooctanoic acid (PFOA), as emerging endocrine-disrupting chemicals (EDCs), pose adverse effects on aquatic organisms. Conventional ecological risk assessment (ERA) not fully considering the mode of toxicity action of PFOS and PFOA, may result in an underestimation of risks and confuse decision-makers. In the study, we developed species sensitivity weighted distribution (SSWD) models based on adverse outcome pathway (AOP) networks for deriving predicted no-effect concentrations (PNECs). Three kinds of weighting criteria (intraspecies variation, trophic level abundance, and data quality) and weighted log-normal distribution methods were adopted. The developed models considered the inter/intraspecies variation and integrated nontraditional endpoints of endocrine-disrupting effects. The PNECs of endocrine disruption effects were derived as 2.52 μg/L (95% confidence intervals 0.667-9.85 μg/L) for PFOS and 18.7 μg/L (5.40-71.0 μg/L) for PFOA, which were more conservative than those derived from the SSD method and were comparable with the values in the literature based on the chronic toxicity data. For PFOS, the effect of growth and development was the most sensitive; however, for PFOA, the effect of reproduction was the most sensitive in the effects of growth and development, reproduction, biochemistry and genetics, and survival. The endocrine-disrupting effects of PFOS and PFOA are significant and need to be fully recognized in the ERA. This study provided an ERA framework that can improve the ecological relevance and reduce the uncertainty of PNECs of EDCs.

Advancements, Challenges, and Future Directions in Aquatic Life Criteria Research in China

Aquatic life criteria (ALC) serve as the scientific foundation for establishing water quality standards, and in China, significant strides have been made in the development of freshwater ALC. This comprehensive review traces the evolution of China's WQC, focusing on the methodological advancements and challenges in priority pollutants selection, test organism screening, and standardized ecotoxicity testing protocols. It also provides a critical evaluation of quality assurance measures, data validation techniques, and minimum data requirements essential for ALC assessments. The paper highlights China's technical guidelines for deriving ALC, and reviews the published values for typical pollutants, assessing their impact on environmental quality standards. Emerging trends and future research avenues are discussed, including the incorporation of molecular toxicology data and the development of predictive models for pollutant toxicity. The review concludes by advocating for a tiered WQC system that accommodates China's diverse ecological regions, thereby offering a robust scientific basis for enhanced water quality management.

Seasonal variation in pesticide residue occurrences in surface waters found in Narok and Bomet Counties, Kenya

Narok and Bomet are agricultural counties in Kenya which depend on flowing surface waters for farming activities. Agrochemicals have frequently been used to increase agricultural produce in this region. Occasionally, appropriate pesticide utilization measures are not followed. These surface waters are also consumed domestically by humans, livestock, and wild animals thus posing safety concerns to them. The current study sought to evaluate the levels and nature of pesticide residues found in surface waters in the dry and wet seasons of these counties. Eight water samples were collected in July (dry season) and October (wet season) at four different river sites in each of the two counties predetermined by the agricultural activity of its proximate environs. Pesticides extracted by solid phase extraction were analyzed by gas chromatography-mass spectrometry. At least 38 different pesticides were detected in the two counties with the highest concentration being recorded for chlorpyrifos and piperidine in Narok and Bomet counties, respectively. The pesticides chlorpyrifos, cypermethrin, cyfluthrin, and cyhalothrin were more prevalent in Narok County while triazine, semicarbazone, and epinephrine were more prevalent in Bomet County. There were significantly more pesticides detected during the wet season (P ≤ 0.05). Out of the nine prevalent pesticides detected, four of them posed serious ecotoxicology concerns with risk quotients above 1.0 (high risk); thus, there is a need for more government policy interventions in deterring farming near riparian lands and in training of famers regarding best practice for pesticide applications.

Understanding hazardous concentrations of microplastics in fresh water using non-traditional toxicity data

Microplastic pollution has become a major environmental problem, indicating the need to implement quantitative governance standards in combination with reducing or banning single-use plastic. Previous studies have predicted no-effect concentrations for limited microplastic-based toxicity data but have not considered environmentally relevant sizes, shapes, or polymers. To provide high quantity and quality data for microplastics of different sizes, shapes, or polymer compositions, non-traditional and traditional toxicity data may need to be considered in combination. In this study, we reviewed toxicity data for microplastics in freshwaters from 2018 to 2022 and analyzed the toxicity data using traditional and non-traditional methods. Based on 166 chronic traditional toxicity data points, the hazard concentration (HC) values calculated from non-traditional toxicity endpoints or all toxicity endpoints were lower than those calculated from traditional toxicity endpoints. Based on 398 chronic traditional plus non-traditional toxicity data points, the HC values calculated from traditional plus non-traditional values were higher than those calculated from traditional toxicity values. With these results, we developed a new framework for deriving microplastic-specific hazardous concentrations, one that especially considers non-traditional toxicity endpoints and values for microplastics. Overall, this study offers a basis for future management strategies and associated frameworks for mitigating microplastic toxicity.

Original and improved interspecies correlation estimation models in China for potential application in water quality criteria

Fluoranthene (FLU) has gained much attention in recent years because of its continuous discharge in natural waters and toxicity to aquatic ecosystems. However, it is difficult to control and manage FLU pollution because of the lack of a rational and scientific water quality criteria (WQC) of FLU. To solve these data gaps, the US EPA established an interspecies correlation estimation (ICE) model, which can be utilized to develop the SSD and HC₅ (hazardous concentration, 5th percentile). Moreover, an improved model was developed using a combination of North American ICE models supplemented with China-specific species. In this study, to verify the applicability of the two ICE models, measured acute toxicity data for FLU were obtained from 9 acute toxicity tests using indigenous Chinese aquatic species from different taxonomic levels. Original and improved ICE-based SSD curves, which were generated using 3 surrogate species (Daphnia magna, Oncorhynchus mykiss, and Lepomis macrochirus), were compared with SSD curves based on measured data. The results showed that HC₅ was 1.838, 1.062, and 0.570 mg/L for the original ICE, improved ICE, and measured data, respectively. The improved ICE-based HC₅ value for FLU was within twofold of the HC₅ value based on measure data, while the original ICE-based HC₅ value was threefold higher than the HC₅ value based on measure data. This indicated that the improved ICE had better predictability in extrapolating data with acceptable deviation than the original ICE. Furthermore, their differences between HC₅ derived from two SSD curves were not significant. Generally, the improved ICE model was verified as a valid approach for generating SSDs with limited toxicity data and for deriving WQC for FLU.

Comparison of the sensitivity between indigenous and exotic aquatic species for fluoranthene and derivation of water quality criteria (WQC)

Fluoranthene (FLU) has shown relatively high toxicity to aquatic life as a priority polycyclic aromatic hydrocarbon (PAH). Considering the toxic effects of FLU on aquatic organisms and its high detection frequency in the aquatic environment, it is necessary and critical to derive FLU water quality criteria (WQC) for the protection of aquatic organisms and ecological risk assessment. However, due to the lack of toxicity data at different classification levels, there has been no research about the WQC of FLU. In this study, nine acute and three chronic toxicity tests were carried out on 9 Chinese indigenous aquatic species from different classification levels to obtain toxicity data. According to the US EPA guidelines, the criterion maximum concentration of 0.570 mg/L and the criterion continuous concentration of 0.174 mg/L were developed. There is no significant difference when comparing the species sensitivity distributions between indigenous and exotic species. Therefore, it is possible to use toxicity data from organisms in different areas for ecological risk assessment of FLU. CAPSULE: We compared the sensitivity between indigenous and exotic aquatic species for fluoranthene and derived its water quality criteria.

Research on freshwater water quality criteria, sediment quality criteria and ecological risk assessment of triclosan in China

Triclosan (TCS) is a broad-spectrum antimicrobial agent commonly used in pharmaceuticals and personal care products (PPCPs). The widespread use of TCS makes it frequently detected in various environmental mediums. In view of the high detection frequency of TCS in the aquatic environment and sediments, and its toxic effects on aquatic species, it is critical and necessary to derive Chinese TCS water quality criteria (WQC) and sediment quality criteria (SQC) for protecting Chinese aquatic organisms, and perform the ecological risk assessment. In fact, former research had derived the WQC of TCS mainly based on acute and chronic toxicity data. As an endocrine disrupting chemical (EDC), TCS poses adverse effects on the growth, development and reproduction of aquatic organisms at much lower concentration. Considering nonlethal endpoints are sensitive endpoints for EDCs, TCS long-term water quality criteria (LWQC) was derived based on reproduction and growth related endpoints. In this work, the acute toxicity data of 19 aquatic organisms and the chronic toxicity data of 15 aquatic organisms were obtained through collection and screening. The best fitting model of species sensitivity distribution (SSD) models including Normal, Log-Normal, Logistic and Log-Logistic of toxicity data was selected to derive WQC. The short-term and long-term WQC of TCS for Chinese aquatic organisms were 6.22 μg/L and 0.25 μg/L, respectively. Furthermore, through the phase-equilibrium partitioning method, SQC was derived based on WQC. SQC-low (SQC-L) and SQC-high (SQCH) were 0.13 mg/kg and 3.26 mg/kg, respectively. Moreover, the exposure concentration (EPC) data of TCS in Chinese rivers and sediments were collected. And through the hazard quotient (HQ) method and the joint probability curve (JPC) method we found that there were certain TCS ecological risks in Chinese rivers and sediments. Our work will provide a valuable reference for protecting aquatic organisms and minimizing TCS ecological risk in China.

Derivation of predicted no effect concentration and ecological risk assessment of polycyclic musks tonalide and galaxolide in sediment

Polycyclic musks (PMs) have drawn increased attention in recent years because of their persistence, bioaccumulation and toxicity. As two typical PMs contaminants, tonalide (AHTN) and galaxolide (HHCB) are widely detected in sediment worldwide. Acute and chronic toxicity data of AHTN and HHCB to freshwater and seawater organisms in water and sediments are collected and screened. The predicted no effect concentrations (PNEC_sediment) for AHTN and HHCB is derived according to the equilibrium partitioning method recommended by the EU technical guidance document (TGD) and the species sensitivity distribution (SSD) method based on the measured sediment toxicity data. The concentration levels of AHTN and HHCB are investigated and evaluated in freshwater and seawater sediments. Results show the difference between native and non-native freshwater species is not statistically significant. AHTN is more toxic to freshwater and seawater organisms than HHCB, and seawater organisms are more sensitive to 2 musks than freshwater organisms. The chronic PNEC_sediment values of AHTN and HHCB are 194.48 and 416.47 ng/g in freshwater sediment, 88.93 and 128.34 ng/g in seawater sediment respectively. The AHTN and HHCB linear correlation analysis exhibited a strong positive linear correlation in both domestic (R²=0.9054) and foreign (R² = 0.9645) sediment. Preliminary risk assessment shows that the risks posed by AHTN and HHCB in sediment based on individual or combined concentrations of two musks are at medium to high levels in some regions. Further risk assessment results indicate that, for HHCB, 1.72% of foreign freshwater sediment may pose an ecological risk to 5% species; for AHTN, 8.06% of foreign freshwater sediment and 1.02% of domestic freshwater sediment may pose an ecological risk to 5% species, and 5.86% of seawater sediment may pose an ecological risk to 5% species. The above results indicate that there are some negligible risks in domestic and foreign sediments posed by these two musks, we should continue to pay attention to the toxic effects and pollution level of both musks in environment.

Development of regional water quality criteria of lead for protecting aquatic organism in Taihu Lake, China

Lead is a widely distributed priority controlled heavy metals in aquatic system, its toxicity to aquatic organisms affected by water quality parameters. This study investigated the acute toxicity of lead (Pb) to the aquatic organisms in Taihu Lake under various water hardness, corresponding regional water quality criteria were derived. The acute toxicity experimental results revealed that the toxicity of Pb to aquatic organisms increased with water hardness. The Pb toxicity has a highest toxicity at water hardness 50 mg/L (expressed as CaCO₃), especially for Palaemon modestus where the 96 h LC₅₀ value was 0.024 mg/L. The hazardous concentration for 5% of biological species (HC₅) values were determined via species sensitivity distribution (SSD) method as 94.0 μg/L, 222.3 μg/L and 375.8 μg/L for Pb at water hardness 50, 150, and 250 mg/L, respectively. The assessment factor (AF) value was set at 2, followed by the current SSD framework where European commission recommend a fixed AF of 5-1. Thus, the predicted no effect concentration (PNEC) values was 47.0 μg/L, 111.2 μg/Land 187.9 μg/L at water hardness 50, 150, and 250 mg/L, respectively. Meanwhile, the short-term water quality criteria of Pb for Taihu lake aquatic organisms were derived as 111.2 μg/L at water hardness 150 mg CaCO₃/L. The long-term water quality criteria were derived as 4.3 μg/L by using acute/chronic ratio 51.29. When the derived value was used for Taihu Lake, 2.7% of the sampling sites in Taihu Lake was exceeded this criterion. The results of this study can provide technical methods and basic information for deriving Pb regional water quality criteria for protecting native aquatic organisms, in China.

Reproductive toxicity due to herbicide exposure in freshwater organisms

Excessively used pesticides in agricultural areas are spilled into aquatic environments, wherein they are suspended or sedimented. Owing to climate change, herbicides are the fastest growing sector of the pesticide industry and are detected in surface water, groundwater, and sediments near agricultural areas. In freshwater, organisms, including mussels, snails, frogs, and fish, are exposed to various types and concentrations of herbicides. Invertebrates are sensitive to herbicide exposure because their defense systems are incomplete. At the top of the food chain in freshwater ecosystems, fish show high bioaccumulation of herbicides. Herbicide exposure causes reproductive toxicity and population declines in freshwater organisms and further contamination of fish used for consumption poses a risk to human health. In addition, it is important to understand how environmental factors are physiologically processed and assess their impacts on reproductive parameters, such as gonadosomatic index and steroid hormone levels. Zebrafish is a good model for examining the effects of herbicides such as atrazine and glyphosate on embryonic development in freshwater fish. This review describes the occurrence and role of herbicides in freshwater environments and their potential implications for the reproduction and embryonic development of freshwater organisms.

Toxic effects of atrazine on immune function in BALB/c mice

This study was aimed to evaluate the toxic effects of different concentrations (23, 90, 360 mg/kg BW) of atrazine (ATZ) on immune function in BALB/c mice. Some parameters of general immunotoxicity, humoral immunity, cellular immunity, and non-specific immunity were tested. The studies showed that the high-dose ATZ induced a significant reduction in the final body weight of mice, the absolute and relative weights of spleen, the counts of white blood cell (WBC), lymphocyte (LYM), monocyte (MON), and the number of splenocyte. An increase in the level of alanine aminotransferase (ALT), aspartate aminotransferase (AST), blood urea nitrogen (BUN), and cholesterol (CHO) in the high-dose ATZ group was observed. Pathological examination showed that the medium- and high-doses of ATZ caused atrophy and destruction of thymus, spleen, and hepatorenal toxicity. The serum interleukin-5(IL-5) level of mice and the number of plaque-forming cell (PFC) in spleen cells in the high-dose ATZ group decreased significantly while there was a significant increase of the serum immunoglobulin G (IgG) in the high-dose ATZ group when compared to the negative control group. In the high-dose ATZ group, the proliferation ability of T and B lymphocytes as well as the delayed-type hypersensitivity (DTH) response were significantly decreased. The low-dose ATZ (23 mg/kg BW) caused a significant decrease in the number of WBC and neutrophil (NEUT), as well as the proportion of polychromatic and normoblast. In summary, we thought the low-dose ATZ has a slight effect on the immune system; it can be preliminarily concluded that the lowest observed adverse effect level (LOAEL) of atrazine is 23 mg/kg BW in mice. Atrazine can cause immunotoxicity mainly through cellular and humoral immunity pathways.

Typical herbicide residues, trophic transfer, bioconcentration, and health risk of marine organisms

Atrazine, a potent herbicide for weeds removal during the growing season, has been widely used in China. It is known to be distributed in aquatic ecosystems with a long half-life, thus presenting a potential risk to species and consumers. This study analyzed the concentrations of degraded atrazine residues in marine organisms (N = 129) including 3 species of mollusks, 2 species of crustaceans, and 15 species of fish from a semi-enclosed bay, Jiaozhou Bay (JZB), adjacent to the Northwest Pacific Ocean in China. The corresponding trophic magnification factors (TMF), bioaccumulation factors (BCFs), and subsequent risks to final consumers were also determined. The results showed an average atrazine concentration of (0.301 ± 0.03) ng g^-1 and (0.305 ± 0.04) ng g^-1 in fish and invertebrates, respectively. The BCFs were (5.23 ± 1.75) L kg^-1 and (5.81 ± 1.31) L kg^-1 for fish and invertebrates, respectively. Atrazine was significantly bio-diluted in JZB through the sampled marine organisms with increasing trophic levels, with a TMF value below 1 (P < 0.01). An analysis of the species sensitivity distribution (SSD) predicted that<0.02% of species were exposed to a dissolved concentration of atrazine (57.88 ng L^-1) that would lead to detrimental effects, while risk quotients predicted low long-term risks for species in the bay. Finally, people with a diet limited to species from JZB were found to face no associated health risk due to a significantly small daily intake and target hazard quotient of atrazine. The corresponding non-carcinogenic effect showed no significant risk from seafood consumption.

Ecological and health risk assessment of perfluorooctane sulfonate in surface and drinking water resources in China

Perfluorooctane sulfonate (PFOS) is a synthetic substance with a great number of applications. However, it persists in the environment and is potentially toxic to organisms. Although China has been the main manufacturer and consumer for PFOS, the national pollution level and potential risk of this chemical are yet to be determined. This study aimed to provide an overview of PFOS contamination in surface and drinking water across China and to assess the potential ecological and health risks. Available monitoring data for PFOS in surface and drinking water were evaluated. PFOS was found to be ubiquitous in China, but the overall level of contamination was low compared with that in other countries. The southeast coastal area of China, with major PFOS-related companies, was characterized by relatively high PFOS exposure concentrations. The most sensitive effects was screened and applied to assess the ecological risk using the joint probability curve method. The probability of exceeding the growth and development toxicity for 5% of aquatic species was 0.65% in Chinese surface waters, while the highest probability of 0.90% was in Tai Lake in east China. Considering the average daily dose (ADD) for the Chinese population, the health risk posed by PFOS through drinking water ranged from 1.31 × 10^-4 to 13.91. Besides the relatively high health risk existed in east China, most health risks in China were acceptable.

Antioxidative enzyme activities in the Rhodeinae sinensis Gunther and Macrobrachium nipponense and multi-endpoint assessment under tonalide exposure

Tonalide or acetyl hexamethyl tetralin (AHTN) is used as a fragrance additive in various household products. Recently, AHTN has drawn attention owing to its negative health effects on aquatic organisms. Data on AHTN toxicity toward aquatic species are limited. Therefore, this study tested the oxidative stress induced by AHTN exposure on the Rhodeinae sinensis Gunther and Macrobrachium nipponense. In this study, malonaldehyde (MDA) content and the activities of acetyl cholinesterase (AchE), superoxide dismutase (SOD), glutathione S-transferase (GST), and catalase (CAT) in R. sinensis Gunther were tested after 30 days of exposure to 30.093, 34.005, 38.426, 43.421, 49.067, 55.444, 62.652, 70.800, and 80.000 μg/L AHTN, respectively. The MDA, AchE, SOD, GST and CAT in M. nipponense were tested after 40 days of exposure to 60.000, 72.000, 86.400, 103.680, 124.416, 149.299, 179.159, 214.991, and 257.989 μg/L AHTN, respectively. In addition, an integrated biomarker response (IBR) index was utilised to evaluate the integrated toxic effects of AHTN on R. sinensis Gunther and M. nipponense. Finally, the predicted no-effect concentrations (PNECs) of AHTN, based on reproduction, biochemistry, survival, chronic toxicity, and acute toxicity endpoints were derived. The results indicated that low concentrations of AHTN can induce significant changes of oxidative stress biomarkers. The no observed effect concentrations (NOECs) of SOD, GST, AchE, CAT, and MDA were 103.680, 72.000, <60.000, 72.000, and <60.000 μg/L for R. sinensis Gunther and 38.426, 43.421, 30.093, 30.093, and 38.426 μg/L for M. nipponense, respectively. The IBR calculation results showed that 149.299 μg/L AHTN caused the highest toxic effect on R. sinensis Gunther after 30 days of exposure, whereas 70.797 μg/L AHTN caused the greatest damage to M. nipponense after 40 days of exposure. The PNECs of AHTN based on the non-traditional endpoints of biochemistry and reproduction were 0.00145 μg/L and 0.000395 μg/L, respectively, which were significantly lower than the PNEC of 2.636 μg/L for traditional endpoint survival. Therefore, the protection of aquatic organisms based on non-traditional toxicity endpoints should be considered in ecological risk assessment.

Hardness-dependent water quality criteria for cadmium and an ecological risk assessment of the Shaying River Basin, China

Hardness is one important water quality parameter that influences the toxicity of cadmium. Several studies have derived water quality criteria (WQC) for cadmium, but most of these studies did not consider environmental factors. Moreover, few studies considered environmental factors when carrying out ecological risk assessments (ERA) based on environmental factors. In this research, six native aquatic organisms in the Shaying River were adopted to conduct toxicity tests for cadmium. By combining published toxicity data for cadmium with hardness values and toxicity data from this study, hardness-dependent WQC were established. When normalized to a hardness of 100 mg/L CaCO₃, the criterion maximum concentration (CMC) of 6.46 μg/L and criterion continuous concentration (CCC) of 1.49 μg/L in the Shaying River Basin were derived according to the USEPA guidelines. The acute predicted no effect concentrations (PNECs) derived by species sensitivity distribution (SSD) methods based on log-logistic, log-normal and Burr Type III models were 1.03, 2.41 and 1.66 μg/L, respectively. Recommended WQC values finally expressed as a function of hardness: (1) CMC=(1.136672-0.041838 × lnH) × e^{0.9969×lnH-2.6676}; and (2) CCC=(1.101672-0.041838 × lnH) × e^{1.0083×lnH-6.1156}. In addition, three tiers of ERA of cadmium in surface waters were conducted based on hardness obtained during different seasons in the Shaying River using the hazard quotient (HQ), the margin of safety (MOS₁₀), and the joint probability (JPC) methods. In tiered 1, 2, and 3 ERA, cadmium exposure concentrations were standardized to a hardness of 100 mg/L. The three levels of the ERA method in the tiered framework gave consistent results: the ecological risks of cadmium in the Shaying River Basin were at acceptable levels. The present study provides a reference for the derivation of WQC and risk assessment of pollution affected by differences in aquatic species and water quality factors such as hardness.

Deriving water quality criteria for China for the organophosphorus pesticides dichlorvos and malathion

Organophosphorus pesticides are effective, cheap, and used extensively but can harm aquatic organism and human health. Here, water quality criteria (WQCs) for dichlorvos (DDVP) and malathion (MAL) were derived. Nine aquatic organisms native to China were used in toxicity tests. Published toxicity data for aquatic organisms native and non-native to China were also analyzed. DDVP and MAL WQCs were derived using (log-normal model) species sensitivity distributions. Species sensitivity distribution curves indicated native and non-native species have different sensitivities to DDVP. The sensitivities of native and non-native species to MAL were not different because non-native species data for fewer than eight genera were available, so further research is required. The results indicated that native species need to be considered when deriving WQCs. The criteria maximum concentration (CMC) and criteria continuous concentration (CCC) were 1.33 and 0.132 μg/L, respectively, for DDVP, and 0.100 and 0.008 μg/L, respectively, for MAL. The CMCs for DDVP and MAL derived using ETX 2.0 software and species sensitivity ranks were different from the CMCs obtained using the SSD method because of parameter uncertainties. The DDVP and MAL WQCs were significantly lower than Chinese surface water quality standard thresholds. The results provide basic data for revising these thresholds.

Exposure and ecological risk of phthalate esters in the Taihu Lake basin, China

The environmental spatial distribution and exposure risk of 6 phthalate esters (PAEs) including dimethyl phthalate (DMP), diethyl phthalate (DEP), butyl benzyl phthalate (BBP), di-n-octyl phthalate (DnOP), bis(2-ethylhexyl) phthalate (DEHP), and dibutyl phthalate (DBP), in surface water and sediment of Taihu Lake basin, China, were investigated at 65 sites. The exposure concentrations of 6 PAEs (∑6PAEs) detected in the samples spanned a range of 0.740-13.0 μg/L in surface water and 5.15-20.9 mg/kg in sediment. DBP and DEHP were the predominant compounds in surface water, with mean concentrations of 1.59 μg/L and 1.29 μg/L, respectively. DnOP was the predominant compound in sediment with mean concentration of 7.41 mg/kg. Ecological risk assessment was conducted by the hazard quotient method in which the predicted no effect concentration (PNEC) was derived from the species sensitivity distribution (SSD) curve. The results showed that DEHP in water phase posed a higher environmental risk than the other PAEs, while the DEP in sediment posed a high risk to the aquatic system. The study contributed to better understanding the presence of PAEs in Taihu Lake basin and provided valuable information for managing and controlling PAEs pollution.

Occurrence, distribution and ecological risk assessment of the herbicide simazine: A case study

The occurrence and distributions of simazine, and its environmental behaviors were studied in Taizi River, China. Results showed that concentration of simazine in surface water and suspended solids (SS) were in the range of 35-1150 ng L^-1and 0.00-1075 ng g^-1 with mean value of 240.26 ng L^-1 and 311.68 ng g^-1, respectively. A significant correlation between the concentrations of simazine and organic carbon was observed in both surface water and SS (r₁ = 0.82, n₁ = 15, r₂ = 0.68, n₂ = 10). and organic carbon in SS was more adsorptive to simazine. Moreover, the concentrations of simazine in groundwater were negatively correlated to the well depths and the distances to the corn fields, and higher concentration of simazine corresponds to younger groundwater. The criterion continuous concentration (CCC) of simazine to Chinese native aquatic species was derived based on the species sensitivity distribution (SSD) to assess the ecological risk. The CCC for simazine was derived to be 4.8 μg L^-1. Furthermore, Ecological risk assessment through risk quotient (RQ) showed that simazine presented low risk (RQ < 0.1) in some of sampling sites, while simazine posed medium risk (0.1 < RQ < 1) only on a few sampling sites nearby corn fields. The study contributed a better sight on the presence of simazine in river and its ecological risk to native aquatic species, and provided information for further studies of simazine potential hazards to the aquatic ecosystem.

Biochemical and histological effects of sub-chronic exposure to atrazine in crayfish Cherax destructor

Atrazine (ATR) is a triazine herbicide banned in the European Union. It remains one of the most widely used herbicides in other parts of the world. Considering the scarcity of data on its possible harm to the environment and to human health, we assessed sub-chronic effects of a 14-day exposure at the environmentally relevant concentration of 6.86 μg/L and at 10% of the 96hLC50 (1.21 mg/L) in crayfish Cherax destructor and their recovery in a 14-day period in ATR-free water. Indicators assessed were behavior; hemolymph biochemical profile; oxidative and antioxidant parameters in gill, hepatopancreas, and muscle; and histology of gill and hepatopancreas. Crayfish exposed to the environmental concentration showed significant differences (P < 0.01) from controls in biochemical parameters of hemolymph (lactate, alkaline phosphatase) and activity of superoxide dismutase, as well as in histology of gill tissue. The higher concentration led to low motor activity, differences in biochemical profile of hemolymph (lactate, alkaline phosphatase, ammonia, glucose), antioxidant biomarkers (superoxide dismutase, catalase, glutathione reductase, glutathione S-transferase, reduced glutathione), as well as gill and hepatopancreas histology. Some observed effects persisted after 14-days recovery in ATR-free water. The results provide evidence that environmental concentrations of ATR produce negative effects on freshwater crayfish.

Effects of environmentally relevant sub-chronic atrazine concentrations on African clawed frog (Xenopus laevis) survival, growth and male gonad development

Sub-chronic toxicity of environmentally relevant atrazine concentrations on exposed tadpoles and adult male African clawed frogs (Xenopus laevis) was evaluated in a quality controlled laboratory for 90 days. The aim of this study was to determine the effects of atrazine on the survival, growth and gonad development of African clawed frogs. After exposure of tadpoles to atrazine concentrations of 0 (control), 0.01, 200 and 500 μg L^-1 in water, mortality rates of 0, 0, 3.3 and 70% respectively were recorded for the 90 day exposure period. Morphometry showed significantly reduced tadpole mass in the 500 μg L^-1 atrazine exposed tadpoles (p < 0.05). Light microscopy on testes of adult frogs exposed to the same atrazine concentrations using hematoxylin and eosin (H&E) and Van Gieson staining techniques revealed gonadal atrophy, disruption of germ cell lines, seminiferous tubule structure damage and formation of extensive connective tissue around seminiferous tubules of frogs exposed to 200 μg L^-1 and 500 μg L^-1 atrazine concentrations. Ultrastructural analysis of the cellular organelles using transmission electron microscopy (TEM) revealed significant amounts of damaged mitochondria in testosterone producing Leydig cells as well as Sertoli cells. Biochemical analysis revealed reduced serum testosterone levels in adult frogs at all exposure levels as well as presence of six atrazine metabolites in frog serum and liver. The results indicate that atrazine concentrations greater than the calculated LC50 of 343.7 μg L^-1 cause significant mortality in tadpoles, while concentrations ≥200 μg L^-1 adversely affect reproductive health of adult frogs and development of tadpoles sub-chronically exposed to atrazine.

How sulfate-rich mine drainage affected aquatic ecosystem degradation in northeastern China, and potential ecological risk

Mining activity is an increasingly important stressor for freshwater ecosystems. However, the mechanism on how sulfate-rich mine drainage affects freshwater ecosystems is largely unknown, and its potential ecological risk has not been assessed so far. During 2009-2016, water and macroinvertebrate samples from 405 sample sites were collected along the mine drainage gradient from circum-neutral to alkaline waters in Hun-Tai River, Northeastern China. Results of linear regressions showed that sulfate-rich mine drainage was significantly positively correlated with the constituents typically derived from rock weathering (Ca²⁺, Mg²⁺ and HCO₃^-+CO₃^2-); the diversity of intolerant stream macroinvertebrates exhibited a steep decline along the gradient of sulfate-rich mine drainage. Meanwhile, stressor-response relationships between sulfate-rich mine drainage and macroinvertebrate communities were explored by two complementary statistical approaches in tandem (Threshold Indicator Taxa Analysis and the field-based method developed by USEPA). Results revealed that once stream sulfate concentrations in mine drainage exceeded 35mg/L, significant decline in the abundance of intolerant macroinvertebrate taxa occurred. An assessment of ecological risk posed by sulfate-rich mine drainage was conducted based on a tiered approach consisting of simple deterministic method (Hazard Quotient, HQ) to probabilistic method (Joint Probability Curve, JPC). Results indicated that sulfate-rich mine drainage posed a potential risk, and 64.62-84.88% of surface waters in Hun-Tai River exist serious risk while 5% threshold (HC₀₅) and 1% threshold (HC₀₁) were set up to protect macroinvertebrates, respectively. This study provided us a better understanding on the impacts of sulfate-rich mine drainage on freshwater ecosystems, and it would be helpful for future catchment management to protect streams from mining activity.