Environmental Concentrations of the Type 2 Diabetes Medication Metformin and Its Transformation Product Guanylurea in Surface Water and Sediment in Ontario and Quebec, Canada.

Metformin, used to treat Type 2 diabetes, is the active ingredient of one of the most prescribed drugs in the world, with over 120 million yearly prescriptions globally. In wastewater-treatment plants (WWTPs), metformin can undergo microbial transformation to form the product guanylurea, which could have toxicological relevance in the environment. Surface water samples from 2018 to 2020 and sediment samples from 2020 were collected from six mixed-use watersheds in Quebec and Ontario, Canada, and analyzed to determine the metformin and guanylurea concentrations at each site. Metformin and guanylurea were present above their limits of quantification in 51.0% and 50.7% of all water samples and in 64% and 21% of all sediment samples, respectively. In surface water, guanylurea was often present at higher concentrations than metformin, while the inverse was true in sediment, with metformin frequently detected at higher concentrations than guanylurea. In addition, at all sites influenced solely by agriculture, concentrations of metformin and guanylurea were <1 µg/L in surface water, suggesting that agriculture is not a significant source of these compounds in the investigated watersheds. These data suggest that WWTPs and potentially septic system leaks are the most likely sources of the compounds in the environment. Guanylurea was detected at many of these sites above environmental concentrations of concern, where critical processes in fish may be affected. Due to the scarcity of available ecotoxicological data and the prominence of guanylurea across all sample sites, there is a need to perform more toxicological investigations of this transformation product and revisit regulations. The present study will help provide toxicologists with environmentally relevant concentration ranges in Canada. Environ Toxicol Chem 2023;42:1709-1720. © 2023 His Majesty the King in Right of Canada and The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. Reproduced with the permission of the Minister of Agriculture and Agri-Food Canada.

Domains of colloidal size, mediated by self-assembly of small molecules in a polymer matrix: a three-level hierarchy of assembly.

Studies on self-assembly of molecules, mediated by, e.g., hydrogen bonding interactions, are a major theme currently. The consequence of such self-assembly of hydrogen-bonding molecules, when dispersed in a polymer matrix, has not been studied so far. We describe such a polymer dispersed self-assembling small molecule system, in which a homologous series of small molecules, with a hydrogen-bonding moiety and alkyl side chains, is dispersed in polycarbonate. These are not liquid crystalline. The self-assembling molecules form colloidal size domains in the polymer, and this involves a hierarchy of three levels of assembly. The molecules self-assemble into small crystallites, which then organize into spherulitic structures. These spherulites then aggregate to form large, uniform near-spherical domains. The size and uniformity of the domains depend on the length of the alkyl side chain. The domain formation is reversible; that is, these domains can be melted and reformed.