Effects of thiamethoxam and neonicotinoid mixtures on early life stages of wild sockeye salmon (Oncorhynchus nerka)

This is the first study to report the acute and chronic effects of environmentally relevant concentrations of thiamethoxam, ranging from 0.15-150 μg/L and a mixture of clothianidin, imidacloprid, and thiamethoxam neonicotinoid pesticides, ranging from 0.045-450 μg/L, on one wild stock of British Columbia sockeye salmon. No effects were observed on growth, development, and a targeted suite of ten genes involved with reproduction, growth, stress response, and nervous and immune function after chronic thiamethoxam or neonicotinoid mixture exposures. However, acute thiamethoxam exposure during fertilization showed reproductive toxicity via a 25% reduction in fertilization success, and subsequent teratogenic effects with abnormal length, weight, and condition factor in swim-up fry in all thiamethoxam and some of neonicotinoid mixture concentrations tested. These findings could have potential implications for wild salmon populations as pulse exposures are environmentally relevant, especially given the amount agriculture and rainfall in the lower Fraser River watershed in British Columbia, Canada.