Derivation of hexachlorocyclohexane toxicity thresholds for assessing ecological risks in the surface waters of China

Although hexachlorocyclohexane (HCHs) being prohibited for a long time in China, they still generally exist in the surface waters and pose a constant threat to aquatic organisms. We retrieved a total of 108 available published literature to assess their ecological risks in the surface waters of China, involving rivers, lakes, and seas. Most of the collected data measured quantifiable HCHs, with the detection rate exceeding 85.0 % for all individual HCHs. A model-averaging species sensitivity distribution (SSD) was constructed to derive the water-quality thresholds of HCHs based on various toxicity endpoints. The results showed that the mortality-based predict no-effect concentration (PNEC) was estimated to be 16.3 and 22.8 μg/L for α-HCH and β-HCH, respectively; The growth-based PNEC at 0.022 μg/L was proposed as the aquatic life criteria of γ-HCH. A certain percentage of aquatic species may face the adverse ecological effect of γ-HCH, with values of potential affected fraction ranging from 0.02 % to 4.76 %. The results of the probabilities of distribution-based quotient (DBQ) exceeding 1/25 showed that the risk of exposure to γ-HCH in the lakes was higher than those in the rivers and sea. The potential-risk sites were mainly located in Yangtze River Basin, Yellow River Basin, Pearl River Basin, and Huaihe River Basin, which belong to the traditional agricultural areas.