CHAPTER 9: Fate of the Antidiabetic Drug Metformin During Chlorine Disinfection of Water

Metformin is the current gold-standard drug for treatment of Diabetes mellitus Type 21 and prescribed at annual quantities of more than 1100 t within Germany.2, 3 It is not metabolized by the human body and only partially degraded during biological wastewater treatment.4 As an environmental pollutant of anthropogenic origin, metformin is present in the range of several hundred ng/L up to one µg/L in most surface waters.5, 6, 7. The production of drinking water from surface waters containing metformin is expected to lead to the formation of disinfection byproducts during chlorine treatment. Scheurer et al. reported that aqueous solutions of metformin rapidly develop an intensive yellow colour upon treatment with sodium hypochlorite (NaOCl; Figure 1).8 Investigations on the chemical reactions taking place during the transformation of metformin by NaOCl led to the discovery of two transformation products Y and C, which are specifically formed during the chlorination of metformin. The primary yellow transformation product Y is a cyclic triazole-derivate with an absorption maximum at 385 nm, carrying an active chlorimino-moiety. It undergoes slow decomposition into the chloroorganic nitrile C, a secondary colourless and stable transformation product.