Contaminants in the Richelieu River (Quebec, Canada) and toxicity to early life stage river (Moxostoma carinatum) and copper redhorse (Moxostoma hubbsi).

Abstract

Early life stage (ELS) fish developing in agricultural rivers may be impacted by exposure to environmental contaminants such as pesticides. We previously reported effects of early life stage (ELS) exposure to contaminated river water in two listed fishes that spawn in the Richelieu River (Quebec, Canada); river redhorse (Moxostoma carinatum; special concern) and copper redhorse (Moxostoma hubbsi; endangered). Here, we characterize temporal and spatial trends in contaminants in surface water collected at two redhorse spawning sites in the Richelieu River and two tributaries during the spawning season. We then used a 14-day ELS bioassay to assess the acute toxicity of four prioritized pesticides in copper and river redhorse. A total of 69 compounds, including pesticides, polybrominated diphenyl ethers, and pharmaceuticals were detected in river water using passive sampling and daily grab samples. Concentrations and frequencies of detection tended to be highest in the tributaries and lowest at the upstream Richelieu location. Levels detected in daily grab samples varied by up to two orders of magnitude throughout the month of June, peaking after large precipitation events. Two neonicotinoid pesticides, thiamethoxam and clothianidin, were measured at concentrations of up to 607 and 199 ng/L respectively, exceeding the Canadian Council of Ministers of the Environment (CCME) environmental quality guideline of 20 ng/L. Four pesticides were prioritized for ELS laboratory toxicity testing at environmentally relevant concentrations in a 14-day static exposure. No effects on hatching time, deformities, or survival were observed, at concentrations as high as 40 µg/L (atrazine), 27 µg/L (metolachlor), 17 µg/L (glyphosate), and 3 µg/L (clothianidin) for both species. Our results suggest that copper and river redhorse are exposed to a complex mixture of contaminants throughout the spawning season and the ELS, but that individually, the four prioritized pesticides are not acutely toxic to these fish at environmental levels during ELS.