Research on the Toxic Effects of Water Treatment By-Product N-Nitrosodimethylamine (NDMA) on Juvenile Crucian Carp

N-nitrosodimethylamine (NDMA) is a relatively toxic and environmentally persistent carcinogen, posing potential threats to the sustainability of freshwater ecosystems, but relevant research on the toxic effects of NDMA in China is relatively scarce. Taking juvenile crucian carp, a key economic and ecological native fish species in China, as the experimental organism, this study explored the acute toxicity and oxidative stress effects of NDMA through semi-static acute toxicity tests combined with 5-day exposure experiments, determining the protein content, superoxide dismutase (SOD), and catalase (CAT) activities in fish. The study provides a reference for ecological risk assessments and pollution control of NDMA in freshwater environments. Results showed that NDMA exerted significant acute toxicity to juvenile crucian carp, with 24, 48, 72, and 96 h half lethal concentrations (LC50) of 9.83, 9.14, 8.11, and 7.05 mg/L, respectively, and a safe concentration (SC) of 0.705 mg/L (classified as medium toxic). NDMA exhibited distinct concentration- and time-dependent effects on the indicators. Protein content showed a consistent induction effect. Low concentrations (1.18, 1.76 mg/L) induced SOD activity, while high concentrations (3.68 mg/L) significantly inhibited it. CAT activity was mainly induced but inhibited in the 3.68 mg/L group at 3–5 days. The inhibition rate order of NDMA on the indicators was SOD > CAT > protein content. This study, through the aforementioned exploration, further supplements domestic toxicological research on NDMA regarding native freshwater fish, clarifies the key acute toxicity parameters and physiological-biochemical response patterns of NDMA on juvenile crucian carp, screens SOD and CAT as potential biomarkers for NDMA pollution monitoring in freshwater environments, and also provides basic data support for the sustainable management of disinfection by-products.