In Switzerland, lake water facilities are equipped with multi-stage treatment systems. However, there are some water companies that feed completely untreated groundwater into the network. Should consumers in those areas expect their drinking water to contain nanoplastics?
Urs von Gunten: When rain percolates into the subsoil, the water first passes through a layer of humus that contains biofilms, such as those in slow sand filtration. These biofilms have proven to be very effective at adsorbing nanoparticles in technical systems. When the water reaches the saturated region, it is also purified by huge sand and gravel filters. The concentration of nanoparticles in the pumped groundwater is therefore likely to be very low. The situation may be different with spring water, as this experiences a much weaker filtration effect than the pumped groundwater. However, given that the springs are largely located in areas with less anthropogenic influences (forests, mountainous areas), this water is only expected to exhibit low concentrations of nanoparticles. Moreover, it is common practice not to use spring water following intensive rainfall, as the turbidity increases rapidly. This measure also serves as a very effective barrier against undesired nanoparticles. Studies into microplastics and nanoplastics are currently underway for both groundwater and spring water.
Your study has produced some very optimistic findings. Do you think the headlines about nanoplastics in drinking water will disappear as a result?
Ralf Kägi: I suspect not. On the one hand, good news is always harder to communicate than bad news. On the other hand, drinking water – as a foodstuff – remains a sensitive area, and one that is full of scientifically unfounded or unprovable theories.