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.

The role of persistence in chemical evaluations.

The initial stage in the assessment and priority setting of chemicals for their potential to cause harm to humans and the environment is usually a hazard assessment employing metrics for persistence, bioaccumulation, and inherent toxicity. This hazard assessment is followed, when necessary, by the more demanding task of risk assessment. Hazard assessment of data and processes influencing persistence are discussed, leading to a number of suggestions for more effective evaluation. These include 1) an initial focus on accurate data for intensive chemical partitioning and reaction half-life properties that are universally applicable as distinct from extensive properties that can be included later on a location-specific basis; 2) separate treatments of near-field and far-field exposures; 3) a focus on persistence and its effect on levels of exposure, especially for substances for which "time to exposure" is less than "time to degradation" and have been termed "pseudo-persistent." We show that "continuously present" is a better descriptor of this concern. Case studies illustrate and support these suggestions. Data on the intensive properties and on exposure pathways are best combined in evaluative multimedia mass balance models that can provide a clear depiction of the likely chemical fate, exposure routes, and levels. The information generated by the mass balance models can serve to justify and direct a full risk assessment that includes region-specific information on chemical quantities, estimates of exposure, and potential for adverse effects.

Modifications of the lactate dehydrogenase assay, a histochemical determinant of osteocyte viability--a qualitative study.

We have refined a technique for assessment of osteocyte viability in a canine and murine model using a modification of the lactate dehydrogenase assay (LDH). With this method, viable osteocytes react to form non-reversible tetrazolium-formazan granules, while non-viable osteocytes are distinguished by a methyl green stain. LDH assay in canine and murine models have not been reported and our initial efforts were not successful. We examined the effect of (a) concentration of coenzyme and tetrazole (b) bone specimen thickness (c) ability to use frozen sections and (d) incubation time/dilution. We concluded that a 1000-fold increase in the concentration of coenzyme and tetrazole were required. Fresh bone produced optimal results and near-complete viability. Special considerations must be taken with smaller, more fragile specimens (e.g., mouse bone), such as increasing specimen thickness, dilution of incubation medium and/or the reduction of incubation time. Sections from thawed frozen bone resulted in a diffuse reaction. Osteocyte viability can be assessed via LDH assay in both dog and mouse bones; however, this approach requires modifications from the previous published method.