Ecotoxicological effects, water quality standards and risk assessment for the anti-diabetic metformin

Metformin (MET) is among the most consumed pharmaceuticals worldwide. This compound has been frequently detected in fresh surface water. However, ecotoxicological information for MET is still too limited, particularly regarding chronic and behavioral data. This study aimed to help filling these knowledge gaps, by carrying out both acute and chronic studies with four different test organisms from three different trophic levels. We assessed different endpoints, including the swimming behavior of Danio rerio larvae. We also derived both short-term and long-term environmental quality standards (EQS) for the protection of freshwater pelagic biota towards MET adverse effects. A risk quotient (RQ) was calculated for MET in fresh surface water, considering a worst-case scenario. Daphnia similis was by far the most sensitive species evaluated. An EC10 of 4.4 mg L-1 was obtained from the reproduction test with D. similis. A long-term EQS of 88 μg L-1 was derived and a RQ of 0.38 was obtained. An ecological risk is not expected for the chronic exposure of pelagic freshwater species to MET, considering the endpoints and the standard bioassays usually recommended in standard protocols. However, endocrine disruptive effects and potential interactive effects of MET with other co-occurring contaminants cannot be ruled out. To the best of our knowledge, this study presents the first data related with MET effects on population endpoints of D. similis and Hydra attenuata, as well as on the locomotor activity of D. rerio.