Freshwater water quality criteria for phthalate esters and recommendations for the revision of the water quality standards.

With increasing urbanization and rapid industrialization, more and more environmental problems have arisen. Phthalates (PAEs) are the foremost and most widespread plasticizers and are readily emitted from these manufactured products into the environment. PAEs act as endocrine-disrupting chemicals (EDCs) and can have serious impacts on aquatic organisms as well as human health. In this study, the water quality criteria (WQC) of five PAEs (dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), butyl benzyl phthalate (BBP) and di(2-ethylhexyl) phthalate (DEHP)) for freshwater aquatic organisms were developed using a species sensitivity distribution (SSD) and a toxicity percentage ranking (TPR) approach. The results showed that long-term water quality criteria (LWQC) of PAEs using the SSD method could be 13.7, 11.1, 2.8, 7.8, and 0.53 µg/L, respectively. Criteria continuous concentrations (CCC) of PAEs were derived using the TPR method and determined to be 28.4, 13.1, 1.3, 2.5, and 1.6 µg/L, respectively. The five PAEs are commonly measured in China surface waters at concentrations between ng/L and µg/L. DBP, DEHP, and di-n-octyl phthalate (DnOP) were the most frequently detected PAEs, with occurrence rates ranging from 67% to 100%. The ecological risk assessment results of PAEs showed a decreasing order of risk at the national level, DEHP, DBP, DMP, DEP, DnOP. The results of this study will be of great benefit to China and other countries in revising water quality standards for the conservation of aquatic species.

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.

Water temperature governs organophosphate ester dynamics in the aquatic food chain of Poyang Lake.

Organophosphate esters (OPEs) are increasingly recognized as pervasive environmental contaminants, primarily from their extensive application in flame retardants and plasticizers. Despite their widespread presence, the intricacies of OPE bioaccumulation within aquatic ecosystems remain poorly understood, particularly the environmental determinants influencing their distribution and the bioaccumulation dynamics across aquatic food chains. Here we show that water temperature plays a crucial role in modulating the dispersion of OPE in the aquatic environment of Poyang Lake. We quantified OPE concentrations across various matrices, uncovering levels ranging from 0.198 to 912.622 ng L-1 in water, 0.013-493.36 ng per g dry weight (dw) in sediment, 0.026-41.92 ng per g wet weight (ww) in plankton, 0.13-2100.72 ng per g dw in benthic invertebrates, and 0.31-3956.49 ng per g dw in wild fish, highlighting a pronounced bioaccumulation gradient. Notably, the intestines emerged as the principal site for OPE absorption, displaying the highest concentrations among the seven tissues examined. Among the various OPEs, tris(chloroethyl) phosphate was distinguished by its significant bioaccumulation potential within the aquatic food web, suggesting a need for heightened scrutiny. The propensity for OPE accumulation was markedly higher in benthic invertebrates than wild fish, indicating a differential vulnerability within aquatic biota. This study lays a foundational basis for the risk assessment of OPEs as emerging contaminants and underscores the imperative to prioritize the examination of bioaccumulation effects, particularly in benthic invertebrates, to inform future environmental safeguarding strategies.

Prediction of HC5s for phthalate esters by use of the QSAR-ICE model and ecological risk assessment in Chinese surface waters.

Due to their endocrine-disrupting effects and the risks posed in surface waters, in particular by chronic low-dose exposure to aquatic organisms, phthalate esters (PAEs) have received significant attention. However, most assessments of risks posed by PAEs were performed at a selection level, and thus limited by empirical data on toxic effects and potencies. A quantitative structure activity relationship (QSAR) and interspecies correlation estimation (ICE) model was constructed to estimate hazardous concentrations (HCs) of selected PAEs to aquatic organisms, then they were used to conduct a multiple-level environmental risk assessment for PAEs in surface waters of China. Values of hazardous concentration for 5% of species (HC5s), based on acute lethality, estimated by use of the QSAR-ICE model were within 1.25-fold of HC5 values derived from empirical data on toxic potency, indicating that the QSAR-ICE model predicts the toxicity of these three PAEs with sufficient accuracy. The five selected PAEs may be commonly measured in China surface waters at concentrations between ng/L and µg/L. Risk quotients according to median concentrations of the five PAEs ranged from 3.24 for di(2-ethylhexhyl) phthalate (DEHP) to 4.10 × 10-3 for dimethyl phthalate (DMP). DEHP and dibutyl phthalate (DBP) had risks to the most vulnerable aquatic biota, with the frequency of exceedances of the predicted no-effect concentration (PNECs) of 75.5% and 38.0%, respectively. DEHP and DBP were identified as having "high" or "moderate" risks. Results of the joint probability curves (JPC) method indicated DEHP posed "intermediate" risk to freshwater species with a maximum risk product of 5.98%. The multiple level system introduced in this study can be used to prioritize chemicals and other new pollutant in the aquatic ecological.

A contrast of emerging contaminants rac- and l-menthol toxicities to Microcystis aeruginosa through biochemical, physiological, and morphological investigations.

Fragrances rac- and l-menthol extracted from peppermint are widely used and considered as emerging contaminants recently, which are persistent in the environment. Menthol has always been considered as a safe chemical for humans, but its potential adverse ecological effects on aquatic organisms and the toxic mechanisms have not yet been fully understood. The present study aims to investigate the physiological response of Microcystis aeruginosa after exposure to the two menthol isomers, and to explore the toxic mechanisms and ecological risks of these two chemicals. Results showed that rac-menthol exhibited a hormesis effect on the cell growth, chlorophyll a and protein contents; while l-menthol showed an inhibition effect. Adenosine triphosphate (ATP) content increased significantly at day 3 and then decreased markedly at day 6 after exposure to the two chemicals. Compared with rac-menthol, l-menthol can cause damage to the antioxidant system and plasmalemma more severely, promote the production and release of microcystins-LR (MC-LR) more dramatically, upregulate the expression of MC-transportation-related gene mcyH, and induce higher apoptosis rates. Overall results revealed that the toxic effects of l-menthol on cyanobacteria were significantly greater than those of rac-menthol. The significant increase in the malondialdehyde (MDA) content and the ultrastructural characteristics of the cells indicated that the plasma membranes were damaged. Thus, further attention should be paid to the scientific use, ecological and environmental risk assessment of chiral menthol. This study will also provide a scientific basis for future water quality criteria establishment on emerging contaminants such as fragrances.

Predicting the acute toxicity of organophosphate esters (OPEs) to aquatic organisms by modelling the structure-toxicity relationships using partial least square regression.

Organophosphate esters (OPEs) have been used worldwide as organophosphate flame retardants (OPFRs) since brominated flame retardants (BFRs) were banned. Due to the toxicity of these OPEs, environmental concerns and ecological risks arose. However, there are still large gaps in the understanding of their toxicity to organisms and the mechanisms of toxicity. After collecting the existing toxicity information and obtaining molecular descriptors of OPEs, a partial least square (PLS) regression model was used in this study to quantify the structure-toxicity relationships of OPEs. Based on the regression results, the acute toxicity of the remaining OPEs lacking acute toxicity data was predicted, and the risk level of total common OPEs was classified. The acute toxicity of 15 chemicals was collected, and >1660 molecular structure descriptors were obtained. The cross-validation results of the partial least square regression indicated that two principal components met the regression requirements with the selected features, and the regression equations of these chemicals were generated with selected molecular descriptors. The influence of physicochemical properties, such as hydrophobicity/molecular weight, in traditional perception of OPE toxicity was not that obvious, and acute toxicity was mainly influenced by the autocorrelation coefficients. However, the regression results indicated that the correlation between autocorrelation coefficients calculated based on different physicochemical properties and toxicity was different. According to the prediction result based on PLS regression, CDP may pose a high risk and halogenated alkyl-substituted OPEs such as TCEP may be less toxic. The results of the present study may help inform the environmental management and risk assessment of emerging chemicals such as OPEs.

[Comprehensive Review on Environmental Biogeochemistry of Nonylphenol and Suggestions for the Management of Emerging Contaminants].

In recent years, China's air environment, water environment, and soil environmental quality have been improved, and a "clear water blue sky" has become a normal state. However, as persistent organic pollutants, endocrine-disrupting chemicals, antibiotics, microplastics, and other emerging contaminants are continuously detected in the environment, these emerging contaminants have gradually been attracting wide attention. Nonylphenol, as a typical endocrine disrupting chemical, has also attracted the attention of researchers. The environmental behaviors and exposure levels of nonylphenol in Chinese water bodies were summarized systematically, and the ecological risks caused by nonylphenol were evaluated based on the risk quotient method and joint probability curve method. The results showed that the toxic effects of nonylphenol on aquatic organisms mainly included acute toxicity, growth and development toxicity, and estrogenic effect and reproductive toxicity. Nonylphenol was commonly found in the water bodies of major drainage areas in China, and the average concentration of nonylphenol ranged from 60 to 1000 ng·L-1, with the highest concentration being as high as 4628 ng·L-1. The results of risk assessment based on the risk quotient method and joint probability curve method showed that nonylphenol had certain risks to aquatic life in the major basins of China. Finally, the commonly used nonylphenol treatment, disposal, and risk management and control technologies were summarized, and the international supervision methods of endocrine-disrupting chemicals were compared. Aiming at addressing the problems existing in China's environmental management, targeted policy suggestions were put forward. The research results can provide reference for the management and control of emerging contaminants in China.

Distribution, Site-Specific Water Quality Criteria, and Ecological Risk Assessment of Heavy Metals in Surface Water in Fen River, China.

Due to a lack of toxicity reference values that match the regional environmental characteristics, the ecological risk of metals in water bodies cannot be accurately assessed. The Fen River is the second-largest tributary of the Yellow River in China, and the sustainability of this area is threatened by heavy metal pollution caused by intensive industrial and agricultural activities. In this study, site-specific water quality criteria (WQCs) for heavy metals in the Fen River were derived considering toxicity data from native aquatic organisms and regional water quality factors (e.g., water hardness). Short-term WQCs for Mn, Cu, Cd, Zn, Cr, Pb, and Ni were 2026.15, 98.62, 10.02, 63.07, 6.06, 166.74, and 132.73 µg/L, respectively, and long-term WQCs were 166.53, 29.71, 2.18, 19.29, 4.15, 6.38, and 14.76 µg/L, respectively. The distribution characteristics of these metals during the wet season in 2020 were explored, and their average concentrations in the river water did not exceed the environmental quality standards for surface water in China but were higher than the world average levels. Cr was the main pollutant in the sampling sites of Yaodu region, Hongdong Shitan, Xiao River, and Duanchun River, as was Pb in Duanchun River. Based on the site-specific WQCs, using hazardous quotient (HQ) and margin of safety (MOS10) approaches, a high risk of Pb was identified in the Duanchun River, and a medium risk of Cr might occur at midstream and downstream of Yaodu and Xiaodian. The results will provide a reference basis for heavy metal pollution control and water quality management in the Fen River.

Research Progress and New Ideas on the Theory and Methodology of Water Quality Criteria for the Protection of Aquatic Organisms.

Water quality criteria (WQC) for the protection of aquatic organisms mainly focus on the maximum threshold values of the pollutants that do not have harmful effects on aquatic organisms. The WQC value is the result obtained based on scientific experiments in the laboratory and data fitting extrapolation and is the limit of the threshold value of pollutants or other harmful factors in the water environment. Until now, many studies have been carried out on WQC for the protection of aquatic organisms internationally, and several countries have also issued their own relevant technical guidelines. Thus, the WQC method for the protection of aquatic organisms has been basically formed, with species sensitivity distribution (SSD) as the main method and the assessment factor (AF) as the auxiliary method. In addition, in terms of the case studies on WQC, many scholars have conducted relevant case studies on various pollutants. At the national level, several countries have also released WQC values for typical pollutants. This study systematically discusses the general situation, theoretical methodology and research progress of WQC for the protection of aquatic organisms, and deeply analyzes the key scientific issues that need to be considered in the research of WQC. Furthermore, combined with the specific characteristics of the emerging pollutants, some new ideas and directions for future WQC research for the protection of aquatic organisms are also proposed.

The Distribution Characteristics and Ecological Risks of Alkylphenols and the Relationships between Alkylphenols and Different Types of Land Use.

In this study, the spatial distribution characteristics of nine alkylphenols (APs) in the Yongding River and Beiyun River were analyzed. The differences in the concentrations and spatial distribution patterns of nine APs were systematically evaluated using principal component analysis (PCA). The relationships between the concentration distribution patterns and the risks associated with nine APs were investigated under various categories of land use conditions in the region. The results demonstrated that the APs were widely present in both rivers, and the pollution risks associated with the APs were more severe in the Yongding River than in the Beiyun River. The results show that the contamination risks associated with 4-NP were the most serious in the two rivers, with detection percentages of 100% and 96.3%, respectively. In the Yongding River, the APs showed a tendency of low concentration levels in the upper reaches and high levels in the middle and lower regions. Meanwhile, the overall concentration levels of the APs in the Beiyun River were relatively high. However, despite the differences between the upper and middle regions of the Yongding River, the distribution pattern of the APs in the Beiyun River was basically stable. The concentration levels and risk quotient of the APs were negatively correlated with the vegetation cover land use type and positively correlated with the cropland and unused land use types within 500 m, 1 km, and 2 km. The purpose of this study was to provide theoretical data support and a basis for AP pollution risk evaluations in the Yongding River and Beiyun River.

Distribution and Characterization of Typical Antibiotics in Water Bodies of the Yellow River Estuary and Their Ecological Risks.

A total of 34 antibiotics from five major classes of antibiotics, including macrolides, sulfonamides, quinolones, tetracyclines and chloramphenicol, were considered as contaminants, considering the Yellow River Estuary as the study area. The distribution, sources and ecological risks of typical antibiotics in the Yellow River Estuary were investigated using an optimized solid-phase extraction pre-treatment and an Agilent 6410B tandem triple-quadrupole liquid chromatography-mass spectrometer for antibiotic detection. The results show that antibiotics were widely present in the water bodies of the Yellow River Estuary, with 14 antibiotics detected to varying degrees, including a high detection rate for lincomycin hydrochloride. Farming wastewater and domestic sewage were the primary sources of antibiotics in the Yellow River Estuary. The distribution characteristics of antibiotics in the study area were linked to the development of farming and social activities. The ecological risk evaluation of 14 antibiotics in the Yellow River Estuary watershed showed that clarithromycin and doxycycline hydrochloride were present at medium-risk levels, and lincomycin hydrochloride, sulfamethoxazole, methomyl, oxifloxacin, enrofloxacin, sulfadiazine, roxithromycin, sulfapyridine, sulfadiazine and ciprofloxacin were present at low-risk levels in the samples collected from water bodies of the Yellow River Estuary. This study provides novel, beneficial information for the assessment of the ecological risk presented by antibiotics in the Yellow River Estuary water bodies and provides a scientific basis for future antibiotic pollution control in the Yellow River Basin.

Freshwater Water-Quality Criteria for Chloride and Guidance for the Revision of the Water-Quality Standard in China.

The chloride in water frequently exceeds the standard; directly quoting foreign water-quality criteria (WQC) or standards will inevitably reduce the scientific value of the water-quality standard (WQS) in China. Additionally, this may lead to the under- or overprotection of water bodies. This study summarized the sources, distribution, pollution status, and hazards of chloride in China's water bodies. Additionally, we compared and analyzed the basis for setting WQS limits for chloride in China; we systematically analyzed the basis for setting the WQC for chloride in foreign countries, especially the United States. Finally, we collected and screened data on the toxicity of chloride to aquatic organisms; we also used the species sensitivity distribution (SSD) method to derive the WQC value for chloride, which is 187.5 mg·L-1. We put forward a recommended value for freshwater WQS for chloride in China: less than 200 mg·L-1. The study of a freshwater WQC for chloride is not only a key point of environmental research, but also an urgent demand to ensure water ecological protection in China. The results of this study are of great significance for the environmental management of chloride, protection of aquatic organisms, and risk assessment, especially for the revision of WQSs.

Ecological risk under the dual threat of heavy metals and antibiotic resistant Escherichia coli in swine-farming wastewater in Shandong Province, China.

Mineral elements and antibiotic-resistant bacterial pollutants in livestock and poultry farms' wastewater are often sources of ecological and public health problems. To understand the heavy-metal pollution status and the characteristics of drug-resistant Escherichia coli (E. coli) in swine-farm wastewater in Shandong Province and to provide guidance for the rational use of mineral-element additives, common antibiotics, and quaternary ammonium compound disinfectants on swine farms, 10 mineral elements were measured and E. coli isolated from wastewater and its resistance to 29 commonly used antibiotics and resistance genes was determined. Finally, phylogenetic and multi-locus sequence typing (MLST) analyses was performed on E. coli. The results showed serious pollution from iron and zinc, with a comprehensive pollution index of 708.94 and 3.13, respectively. It is worth noting that average iron levels in 75% (12/16) of the districts exceed allowable limits. Multidrug-resistant E. coli were found in every city of the province. The E. coli isolated from swine-farm wastewater were mainly resistant to tetracyclines (95.3%), chloramphenicol (77.8%), and sulfonamides (62.2%), while antibiotic resistance genes for quinolones, tetracyclines, sulfonamides, aminoglycosides, and ß-lactams were all more than 60%. The clonal complex 10 (CC10) was prevalent, and ST10 and ST48 were dominant in E. coli isolates. Multidrug-resistant E. coli were widely distributed, with mainly A genotypes. However, the mechanism of the effect of iron on antibiotic resistance needs more study in this area. Thus, further strengthening the prevention and control of iron and zinc pollution and standardizing the use of antibiotics and mineral element additives in the swine industry are necessary.

Insights into the geographical distribution, bioaccumulation characteristics, and ecological risks of organophosphate esters.

Organophosphate esters (OPEs), as flame retardants and plasticizers, have been numerously explored regarding the occurrence and ecotoxicology. Given their toxicity, persistency and bio-accumulative potential, however, they may pose negative effects on ecosystems, regarding which is a growing global concern. Accordingly, the present review systematically analyses the recent literature to (1) elucidate their worldwide distribution, bioaccumulation, and biomagnification potential, (2) determine their interim water quality criteria (i.e., effect thresholds), and (3) preliminarily assess the ecological risks for 32 OPEs in aquatic ecosystems. The results showed that the spatiotemporal distribution of OPEs was geographically specific and closely related to human activities (i.e., megacities), especially halogenated-OPEs. We also found that precipitation of airborne particulates could affect the concentrations of OPEs in soil, and there was a positive correlation between the bioaccumulation and hydrophobicity of OPEs. Tris(2-ethylhexyl) phosphate may exhibit high bioaccumulation in aquatic organisms. A substantial difference was found among interim water quality criteria for OPEs, partly attributable to the variation of their available toxicity data. Tris(phenyl) phosphate (TPHP) and tris(1,3-dichloroisopropyl) phosphate with the lowest predicted no-effect concentration showed the strongest toxicity of growth and reproduction. Through the application of the risk quotient and joint probability curve, TPHP and tris(chloroethyl) phosphate tended to pose moderate risks, which should receive more attention for risk management. Future research should focus on knowledge gaps in the mechanism of biomagnification, derivation of water quality criteria, and more precise assessment of ecological risks for OPEs.

Toxicity mechanisms and bioavailability of copper to fish based on an adverse outcome pathway analysis.

Copper (Cu) exists in a variety of forms in different aquatic environments, and affects their bioavailability. In this study we provide a systematic review on toxicity of Cu which focuses on identifying evidence in the mechanisms of Cu toxicity, and apply an adverse outcome pathway (AOP) analysis to identify multiple potential mechanisms and their interactions of Cu toxicity to fish. This analysis process included the mechanisms of behavior toxicant, oxidative toxicant, ion regulation disruption toxicity, as well as endocrine disruption toxicity. It was found that at low levels of Cu exposure, swimming, avoid predators, locating prey and other sensory functions will be impaired, and the organism will suffer from metabolic alkalosis and respiratory acidosis following the inhibition of the carbonic anhydrase active. The main pathway of acute toxicity of Cu to fish is the inhibition of the Na+/K+-ATPase enzyme, and lead to reduced intracellular sodium absorption, as well as Cu-induced increased cell permeability, in turn resulting in increased sodium ion loss, leading to cardiovascular collapse and respiratory insufficiency. The endocrine disruption toxicity of Cu to fish caused growth inhibition and reproductive reduction. In addition, there are several key pathways of Cu toxicity that are affected by hardness (e.g., Ca2+) and intracellular DOC concentrations, including inhibiting Cu-induction, improving branchial gas exchange, altering membrane transport functions, decreasing Na+ loss, and increasing Na+ uptake. The results of the AOP analysis will provide a robust framework for future directed research on the mechanisms of Cu toxicity.

Organophosphate esters cause thyroid dysfunction via multiple signaling pathways in zebrafish brain.

Organophosphate esters (OPEs) are widespread in various environmental media, and can disrupt thyroid endocrine signaling pathways. Mechanisms by which OPEs disrupt thyroid hormone (TH) signal transduction are not fully understood. Here, we present in vivo-in vitro-in silico evidence establishing OPEs as environmental THs competitively entering the brain to inhibit growth of zebrafish via multiple signaling pathways. OPEs can bind to transthyretin (TTR) and thyroxine-binding globulin, thereby affecting the transport of TH in the blood, and to the brain by TTR through the blood-brain barrier. When GH3 cells were exposed to OPEs, cell proliferation was significantly inhibited given that OPEs are competitive inhibitors of TH. Cresyl diphenyl phosphate was shown to be an effective antagonist of TH. Chronic exposure to OPEs significantly inhibited the growth of zebrafish by interfering with thyroperoxidase and thyroglobulin to inhibit TH synthesis. Based on comparisons of modulations of gene expression with the Gene Ontology and Kyoto Encyclopedia of Genes and Genomes databases, signaling pathways related to thyroid endocrine functions, such as receptor-ligand binding and regulation of hormone levels, were identified as being affected by exposure to OPEs. Effects were also associated with the biosynthesis and metabolism of lipids, and neuroactive ligand-receptor interactions. These findings provide a comprehensive understanding of the mechanisms by which OPEs disrupt thyroid pathways in zebrafish.

A QSAR-ICE-SSD model prediction of the PNECs for alkylphenol substances and application in ecological risk assessment for rivers of a megacity.

Alkylphenols (APs) are ubiquitous and generally present in higher residue levels in the environment. The present work focuses on the development of a set of in silico models to predict the aquatic toxicity of APs with incomplete/unknown toxicity data in aquatic environments. To achieve this, a QSAR-ICE-SSD model was constructed for aquatic organisms by combining quantitative structure-activity relationship (QSAR), interspecies correlation estimation (ICE), and species sensitivity distribution (SSD) models in order to obtain the hazardous concentrations (HCs) of selected APs. The research indicated that the keywords "alkylphenol" and "nonylphenol" were most commonly studied. The selected ICE models were robust (R2: 0.70-0.99; p-value < 0.01). All models had a high reliability cross- validation success rates (>75%), and the HC5 predicted with the QSAR-ICE-SSD model was 2-fold than that derived with measured experimental data. The HC5 values demonstrated nearly linear decreasing trend from 2-MP to 4-HTP, while the decreasing trend from 4-HTP to 4-DP became shallower, indicates that the toxicity of APs to aquatic organisms increases with the addition of alkyl carbon chain lengths. The ecological risks assessment (ERA) of APs revealed that aquatic organisms were at risk from exposure to 4-NP at most river stations (the highest risk quotient (RQ) = 1.51), with the highest relative risk associated with 2.9% of 4-NP detected in 82.9% of the sampling sites. The targeted APs posed potential ecological risks in the Yongding and Beiyun River according to the mixture ERA. The potential application of QSAR-ICE-SSD models could satisfy the immediate needs for HC5 derivations without the need for additional in vivo testing.

Hardness-Dependent Water Quality Criteria for Protection of Freshwater Aquatic Organisms for Silver in China.

Silver is toxic to freshwater aquatic organisms and aquatic ecosystems, and it is necessary to develop regional water quality criteria (WQC) for silver to protect the freshwater aquatic organisms in China. The toxicity database of silver for freshwater aquatic organisms involved 121 acute toxicity values for 35 species (6 phyla and 27 families) and 15 chronic toxicity values for 4 species (2 phyla and 4 families). Teleost fish showed the most sensitivity to silver after both short-term and long-term exposure. Significant correlations between the natural logarithms of hardness and the natural logarithms of acute silver toxicity were found for Daphnia magna, Oncorhynchus mykiss, and Pimephales promelas. The criterion maximum concentration (CMC) was calculated by the species sensitivity distribution method with sigmoid as the best fitting model (Adj R2 0.9797), and the criterion continuous concentration (CCC) was obtained by the acute-to-chronic ratio method. The CMC and CCC of silver were e1.58ln(HCaCO3)-8.68, and e1.58ln(HCaCO3)-10.28 respectively, in China, with water hardness (HCaCO3, mg/L) as an independent variable. This research can provide a basis and reference for the management of silver to protect freshwater aquatic organisms in China.

Water quality criteria for lanthanum for freshwater aquatic organisms derived via species sensitivity distributions and interspecies correlation estimation models.

The increasing exploitation and application of rare earth elements (REEs) may induce hazardous risks to freshwater aquatic organisms. Due to the lack of water quality criteria (WQC) and sufficient reliable toxicity data, little information is available on the ecological risk of REEs in surface water. In this study, lanthanum (La) toxicity data were collected from published toxicological studies, and the data quality was assessed using a toxicological data reliability assessment tool. To obtain more toxicity data, Daphnia magna, Cyprinus carpio, and Dania rerio embryos were selected as surrogate species, and an interspecies correlation estimation (ICE) model was used to predict the toxicity of La for untested species. The species sensitivity distributions (SSDs) of La toxicity and WQC were investigated. Differences were observed in the hazardous concentrations for 5% of species (HC5), but no statistically significant differences were noted in the SSD curves between the measured acute toxicity data and the predicted data. For the SSDs constructed from the measured toxicity data, the ICE-predicted toxicity data and all acute data supplemented with the ICE-predicted data, the acute WQC values of La were 88, 1022 and 256 µg/L, respectively. According to the SSD and corresponding HC5 of chronic toxicity data, the chronic WQC was 14 µg/L. The results provide a scientific reference for establishing WQC for freshwater aquatic organisms and ecological risk assessments of REEs.