What's in your water? A comparative analysis of micro- and nanoplastics in treated drinking water and bottled water

Micro- and nanoplastic (MNP) contamination in drinking water is of growing concern due to the potential for human health risks associated with their ingestion and subsequent cellular uptake. Microplastics (MPs) have seen extensive study, but nanoplastics (NPs) have not and NP presence in drinking water remains poorly understood. This primarily reflects limitations in the methods to isolate and analyze the NPs. In this study, we developed and validated a novel method for isolating MNPs allowing for the determination of their concentrations using scanning electron microscopy (SEM) and identification using optical photothermal infrared spectroscopy (OPTIR). The use of OPTIR allows polymer determination of submicron-sized particles, which is an order of magnitude smaller than comparable spectroscopic techniques. This method was applied to samples collected from four drinking water treatment plants and six brands of bottled water. While this method does not have an upper limit of quantification, the results from this study identified MNPs ranging from 300 nm to 42.3 μm. The results showed bottled water had significantly higher particle concentrations of MNPs than the treated drinking water, specifically for the smaller micro- and nanoplastics. Bottled water had a high abundance of polyamide (PA), polyethylene terephthalate (PET), and polyethylene (PE), while treated drinking water was most abundant in PA and polyesters (PES including PET). Rubber was an important MNP in many of the analyzed waters and it was identified in every sample. This suggests elastomeric MNPs may be more prevalent than previously thought, as prior studies evaluating MNPs in drinking water do not report these polymers despite their documented abundance in other environmental samples. The findings from this study suggest prior studies underestimate MNP concentrations in both sample types due to the exclusion of nanoplastics, and that bottled water may have a higher prevalence of MNPs than conventionally treated municipal drinking water.