The review assesses the quality of microplastic occurrence studies in drinking-water, freshwater and wastewater. It also summarizes the data on microplastic concentrations, polymer types, and particle shapes in these water environments and proposes best practices for microplastic occurrence studies. Most importantly, the study provides a refined grading system to evaluate the quality and reliability of data reported in the literature.

No harmful effects on humans
The review’s authors draw on a comprehensive examination of the best available evidence from the literature on microplastics in drinking water and its sources. They highlight that microplastics – tiny particles under 5mm in length – are present in all water types examined. These particles come from a variety of sources, including plastic products, textiles, fisheries, agriculture, industry and general waste. In controlled experiments, high concentrations of these particles have been shown to cause physical harm to the environment and living creatures, including inducing inflammation and stress. However, to date, no harmful effects on humans have been demonstrated.

Need to improve measurements
Professor Bart Koelmans, first author of the review, said: “The evidence about microplastics in our drinking water remains uncertain, but we now see that for the main part this stems from unreliable methodologies. This hampers the assessment of risks these tiny particles might pose for the environment and human health. Obviously, a lack of reliability in the data does not imply we can assume that there is no risk. For sure we need to improve and harmonize measurement methods for microplastics to be able to monitor their concentrations over time and space. Besides drinking water, this need concerns other food stuffs as well.”

Microplastics in freshwaters and drinking water: Critical review and assessment of data quality; Water Research