Water Quality Criteria And Ecological Risk Assessment For Chlorophenols Based On Native Species In China

With rapid economic development in China, the amount of synthetic chemicals is increasing rapidly and lots of them are released into the aquatic environment, which causes serious harm to the aquatic ecosystem. Water quality standards (WQSs) are playing a very important role in environment management and pollution control. However, the current standards in China are derived directly from and/or based on WQSs or water quality criteria (WQC) of developed countries. WQC is a major component of WQSs, it supports essential scientific evidence for derivation of WQSs. While the establishment of WQC is usually based on the toxicity on regional aquatic organisms considering regional eco-environmental characteristics, thus WQC in different countries or even different regions in one country are not always the same. Due to that, China has begun to embark on development of its own national WQC system based on its resident aquatic organisms and geographic eco-environmental characteristics.In this study, several widely used statistical extrapolation methods, belong to species sensitivity distribution (SSD), were compared. Taking three ubiquitous chlorophenols (CPs):2,4-dichlorophenol (2,4-DCP),2,4,6-trichlorophenol (2,4,6-TCP) and pentachlorophenol (PCP), for example, effects of pH on the toxicity of the three CPs were studied using organisms Daphnia magna and Scenedesmus obliquus; furthermore, combined the previous studies, the WQC expressed as functions of pH derived from SSD considering intraspecies variation or/and proportions of taxonomic groups were recommended. In addition, combined toxicity of the three CPs, including binary and ternary mixtures, was investigated using Daphnia magna. Finally, ecological risk assessment of individuals and mixture of the three CPs in surface water in China were investigated.Comparison of different SSD methods indicated that parametric and nonparametric methods can both describe the toxicity data well. There were strong correlations between different methods. Especially, nonparametric bootstrap method is visually the best-fitting model. In spite that the goodness of fit in different parametric methods were not the same, they almost could describe the toxicity data well (R2>0.90).Toxicity of2,4-DCP,2,4,6-TCP and PCP to aquatic organisms all decreased with increasing pH values. The recommended WQC were functions of pH. At pH7.8, acute WQC were286.20μg/L for2,4-DCP,341.53μg/L for2,4,6-TCP and11.39μg/L for PCP, respectively; chronic WQC were16.25μg/L for2,4-DCP,54.61μg/L for2,4,6-TCP and3.90μg/L for PCP, respectively. These updated criteria with more convincing evidence are useful in determination of water quality standards and management of environment.Combined toxicity of three CPs to Daphnia magna showed that mathematical model was a flexible and effective method to predict toxicity of chemical mixtures. Response surface relationships were established for any binary mixtures of three CPs. Concentration addition (CA) or toxicity equivalency factors (TEF) model could predict toxic effects for binary CPs mixtures, but underestimated the toxic effects of CPs ternary mixture.Ecological risk assessment of three CPs in surface water in China showed that the potential adverse effects of2,4-DCP or2,4,6-TCP were relatively small for both the median and maximum exposure concentrations, which the probabilities of concentration exceeding the concentration likely to adversely affect5%of species were5.99%and21.36%, respectively. The probabilities of affecting5%of aquatic species for PCP were21.36%and5.99%for the maximum and median concentrations, respectively. The probabilities of affecting5%of aquatic organisms for mixtures of CPs were49.83%and12.72%for the maximum and median concentrations, respectively.