Freshwater Quality Criteria for the Protection of Aquatic Life and Ecological Risk Assessment for Sulfamethoxazole in China

Sulfamethoxazole (SMX) has adverse effects on aquatic life, including algae, crustaceans, and even fish. However, the freshwater quality criteria for the protection of aquatic life (ALFQC) of SMX are still unclear, as well as its ecological risk for surface waters in China. The acute and chronic toxicity data for SMX covered 10 and 11 species, respectively, which are widely distributed across China. The native species in China of Raphidocelis subcapitata displayed the most sensitivity after short-term exposure, whereas Lemna gibba showed the most sensitivity after long-term exposure to water contaminated with SMX. The short-term and long-term ALFQC of SMX were 2829 and 23.63 µg/L, respectively using the species sensitivity distribution in China. The 112 exposure data were collected from peer-reviewed publications and government reports published between 2006 and 2024, with the concentrations of SMX ranging from 0 to 0.531 µg/L in surface waters in China. A negligible ecological risk of SMX was observed in surface waters in China, confirmed by the low risk quotient (0~0.0225) and probability area overlap (0~0.005). This study provides a scientific basis for water quality standards and the ecological risk management for SMX in surface waters in China.