Analysis of microplastic particles in Danish drinking water

Microplastic (MP) is a pervasive pollutant found in sediment, water and biota throughout the world. However, the extent to which humans are exposed to this contaminant is not well researched. Recently studies have indicated that MP is also present in tap water, bottled water and food destined for human consumption. Here, we investigate the presence of MP in drinking water from 17 sites around Denmark. 50 L of drinking water were sampled per site directly from taps through 10 µm stainless steel filters in a closed steel filter system to prevent contamination. The filters were examined visually by stereomicroscopy and the number and characteristics of all MP-like particles with sizes > 100 µm were registered – i.e. particles which were either potential MP or particles of uncertain origin that might be MP. 124 (44 %) MP-like particles representatively selected among the particles from the filters were then manually transferred to ZnSe discs and the chemical composition identified using advanced µFT-IR utilizing focal plane array (128 x 128) mapping with a pixel resolution of 5.5 µm. Additionally, three tap water samples were passed directly through Anodisc filters (ø 2.5 cm, pore size 0.2 µm) for additional chemical µFT-IR analysis to detect potential MP < 100 µm. This analysis mapped particles in 10 % of the Anodisc filter area (corresponding to 10 % of all particles per sample), and the direct transfer process meant that any potential bias from visual picking of particles could be excluded. The results from the visual assessment of filters showed that in average 15.6 MP-like particles > 100 µm were observed per 50 L water sample. In 16 of the 17 samples, the number were below the limit of detection (29 per 50 L) and in the sample with the highest concentration, 30 MP-like particles per 50 L were observed. Identification by ZnSe discs showed that 3 % of the MP-like particles were verified as MP, whereas the majority consisted of cellulose-like material (76 %), and the rest were poor spectra (10 %), unknown (7 %) or proteinlike (4 %). The types of MP particles detected in the tap water samples were polyethylene terephthalate, polypropylene and polystyrene. Using the Anodisc method, polyethylene terephthalate and polypropylene were also found, as well as acrylonitrile butadiene styrene and polyurethane. However, due to the concentrations of MP below the limit of detection, no conclusions regarding the origin of MP from either tap water or sample contamination can be made. In contrast to previous American and Danish studies of MP in drinking water, which were highly publicised by the media, this study shows no significant concentrations of MP in Danish tap water. This result is in line with a recent study of Norwegian drinking water from 2018.