A global perspective on the use, occurrence, fate and effects of anti-diabetic drug metformin in natural and engineered ecosystems.

Metformin is the most commonly used anti-diabetic drug in the world. When consumed, this unmetabolised pharmaceutical compound is excreted by the body and eventually enters the environment through a variety of pathways. Based on its high consumption and excretion rates, high concentrations of metformin have been detected in influents of wastewater treatment plants. Metformin and its transformation product, guanylurea, are also expected to be present in other aquatic environments based on their physico-chemical properties. Not surprisingly, guanylurea has also been detected in surface water, groundwater, and drinking water. Available information on ecotoxicological effects of metformin suggests that metformin is a potential endocrine disruptor and thus further emphasising the threat this drug could pose to our environment. This review provides a comprehensive overview of metformin and critically discusses available literature data with respect to its global use/demand, occurrence, fate and ecotoxicity in treatment facilities equipped with conventional and advanced treatment technologies, and its degradation/removal mechanisms. Final section highlights the existing knowledge gaps regarding its ultimate fate under the natural and engineered ecosystems and identifies some important research areas requiring urgent attention from regulatory makers and scientific community.