Perturbations in the earthworm metabolite profile during a two-week exposure to metformin

Metformin is among the most prescribed pharmaceuticals in many countries, and as a result has shown up in biosolids derived from municipal wastewater treatment that are destined for land application. In humans taking metformin, the effects include reduced glucose uptake in the intestine, a reduction in gluconeogenesis, increased oxidation of fatty acids, and reduced fatty acid synthesis. The effects of metformin on soil-dwelling organisms are not well understood. This study tested the effects of metformin exposure (0, 10, 40, 160, 640 μg g⁻¹) on the earthworm (E. fetida) at four time points (6 h, 2 d, 7 d, and 14 d) using GC-MS to reveal sub-lethal effects and elucidate potential modes of action for metformin. There were no mortalities observed, and earthworms exposed to the highest concentrations (160 and 640 μg g⁻¹) gained weight relative to the control on days 7 and 14. Significant reductions on day 7 were observed for glucose and malic acid (consistent with a reduction in gluconeogenesis), and for palmitic and margaric acid (consistent with increased oxidation and reduced synthesis of fatty acids). Lactic acid ranked first and second among canonicals 1 and 2 respectively and led to significant differences in discriminant scores across concentration and time. Metabolite levels increased to equal or greater than the control on day 14, likely caused by reduced exposure as metformin is reported to be readily transformed by microorganisms under aerobic conditions. The observations were consistent with the known effects of metformin in humans, and suggests that a similar mode of action exists in earthworms.