Impacts of methamphetamine and ketamine on C.elegans's physiological functions at environmentally relevant concentrations and eco-risk assessment in surface waters

In this work, C. elegans as a model organism was treated with methamphetamine (METH) and ketamine (KET) to assess its eco-toxicity at a range (0.05-250 μg L^-1) that covers environmentally relevant concentrations (0.05-0.5 μg L^-1). METH (≥0.05 μg L^-1) and KET (≥0.5 μg L^-1) significantly affected the feeding rate, locomotion, gustation and olfaction (P < 0.05), which may result in pronounced disturbance to aquatic ecology. Alterations in the contents of neurotransmitters (i.e., octopamine (OA), dopamine (DA), and serotonin (5-HT)) correlated with the physiology change. The metabolic activities and the antioxidase activity (i.e., superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)) of METH and KET in C. elegans were different, which could partly explain the difference of the physiological changes induced by the two substances. Moreover, these two drugs could induce vulva deformity, and the 50% effect concentrations were 620.34 μg L^-1 for METH and 54.39 μg L^-1 for KET, respectively. The risk quotients (RQ) in two Chinese rivers, the Shenzhen and Liangshui River, were calculated to assess eco-risks of METH and KET. RQs of KET in the Shenzhen River were over 0.1 at the medium risk level, indicating that eco-risks of illicit drugs to aquatic organism cannot be overlooked.