Microplastics and nitrogenous disinfection byproducts in drinking water: complex interactions beyond adsorption

Abstract Microplastics (MPs) in drinking water are an emerging concern due to their potential health risks, environmental impacts, and ability to adsorb organic micropollutants. Nitrogenous disinfection byproducts (DBPs), which are generally more toxic than the regulated DBPs, may interact with MPs via hydrophobic or electrostatic mechanisms. Such interactions raise concern that MPs in treated water could concentrate toxic DBPs during distribution or storage, increasing potential human exposure beyond the risks posed by either MPs or DBPs alone. This study investigates the adsorption behavior of select DBPs, including nitrogenous DBPs like N-nitrosodimethylamine (NDMA) and halonitromethanes (HNMs), as well as trihalomethanes (THMs), which are included for comparison as the most commonly regulated DBPs, onto virgin and weathered MPs. The polymers studied include polyethylene (PE), polypropylene (PP), polyvinyl chloride (PVC), polyamide (PA), polyacrylonitrile (PAN), and polyethylene terephthalate (PET). The results indicate that hydrophobic DBPs such as THMs adsorb onto both virgin and weathered PVC at levels of roughly 10–20 µg/g. Hydrophilic DBPs like NDMA show negligible adsorption on hydrophobic microplastics but greater interaction with hydrophilic polymers such as PET, at roughly 10 ng/g. In addition, trichloronitromethane degrades completely in the presence of PA, and weathered PA accelerates this process, with full degradation and conversion to DCNM observed within 14 days. Given that these DBPs and MPs represent a small fraction of the total to be considered, it is clear that there is much work to be done to fully evaluate the possible interactions and potential for human health effects.