Environmental risk assessment of metformin and its transformation product guanylurea. I. Environmental fate. (February 2019)

• Record Type: Journal Article
• Authors: Straub, Jürg Oliver; Caldwell, Daniel J.; Davidson, Todd; D'Aco, Vincent; Kappler, Kelly; Robinson, Paul F.; Simon-Hettich, Brigitte; Tell, Joan
• Is Part Of: Chemosphere. Volume 216(2019)
• Page Start: 844
• Page End: 854
• Publication Date: 2019-02
• Subjects: Metformin -- Guanylurea -- Environmental fate -- Transformation -- Biodegradation; Pollution -- Periodicals; Pollution -- Physiological effect -- Periodicals; Environmental sciences -- Periodicals; Atmospheric chemistry -- Periodicals; 551.511
• DOI: 10.1016/j.chemosphere.2018.10.036
• Languages: English
• ISSNs: 0045-6535

Abstract

Abstract: Metformin (MET) is a pharmaceutical with very high use worldwide that is excreted in unchanged form, leading to concern about potential aquatic life impacts associated with MET, and its primary transformation product guanylurea (GUU). This study presents, in two companion papers, a risk assessment following internationally accepted guidelines of MET and GUU in surface water based on literature data, previously unpublished studies, and a new degradation test that resolves conflicting earlier results. Previous studies have shown that MET is removed during sewage treatment, primarily through transformation to GUU. In addition, measurements in WWTPs suggest that MET is not only transformed to GUU, but that GUU is further biodegraded. A prolonged inherent biodegradation test strongly suggests not only primary transformation of MET to GUU, but also subsequent full mineralization of GUU, with both degradation phases starting after a clear lag phase. MET may partition from surface water to sediment, where both transformation to GUU and in part mineralization is possible, depending on the presence of competent degrading microorganisms. In addition, MET may form non-extractable residues in sediments (12.8–73.5%). Both MET and GUU may be anaerobically degraded during sludge digestion, in soils or in sediments. Bioconcentration factor (BCF) values in crops and most plants are close to 1 suggesting low bioaccumulation potential, moreover, at least some plants can metabolize MET to GUU; however, in aquatic plants higher BCFs were found, up to 53. Similarly, neither MET nor GUU are expected to bioaccumulate in fish based on estimated values of BCFs ≤3.16. Highlights: The environmental fate of metformin (MET) and guanylurea (GUU) is discussed. Both peer-reviewed literature and unpublished, quality industry studies are integrated. New data not only suggest degradation of MET to GUU, but also full mineralization. MET partitions to sediment with a fraction as non-extractable residue. MET and GUU are not expected to bioaccumulate in fish.