Recently, the presence of plastics in water environment has gained considerable attention. Not only plastic litter that is visible to the naked eye, but also smaller debris – recognized as microplastics – are of a great interest. Microplastics (MPs; plastic particles smaller than 5 mm) have been detected in different water bodies, i.e. oceans, seas and freshwaters, including those that serve as sources for water treatment plants and therefore for the production of drinking water. Despite neither the effect of MPs on human health nor their ecological impacts are known, microplastics are considered to be an emerging contaminant that deserves particular attention.
Microplastics are usually defined as particles smaller than 5 mm, while the lower limit is not clearly stated. Microplastics down to the size of 1 µm have been detected in natural waters and it can be estimated that even smaller particles (nanoplastics) might be present. However, these cannot be credibly analysed by the current available methods for MPs detection. Nevertheless, some studies observed that the size distribution of MPs tends to skew towards smaller sizes. The substantial occurrence of MPs was revealed in various water bodies (oceans, seas, lakes, rivers, artificial dams) across the continents. Additionally, there are few studies that proved the presence of MPs also in selected packed beverages or foodstuffs. However, the research on microplastics is still in its beginning stages and studies on MPs in drinking water are lacking.
Microplastics can be divided into primary and secondary, according to their origin. Primary MPs are those that were directly utilized in consumer products such as cosmetics or cleaners. Secondary MPs are formed by disintegration of larger items, e.g. by release of synthetic fibres during washing of clothes or decomposition of plastic waste. An important source of microplastics in freshwaters is probably sewage discharge. Despite conventional waste water treatment plants have shown an ability to remove a part of microplastics, large amounts of MPs pass through the process, accounting for up to thousands particles per m3 effluent.
In general, ecological and toxicological impacts of MPs are largely unknown. However, laboratory experiments simulating exposure to MPs conducted on some aquatic species revealed adverse effects on the organisms. Besides intrinsic impacts of MPs, they can also serve as a transfer medium for other harmful chemicals.
Research at the Institute of Hydrodynamics
In general, there is lack of information about microplastics in drinking water sources. The research performed at the Institute of Hydrodynamics proved the presence of MPs in both raw and treated drinking water. Investigating the content of MPs both in the sources of water and in drinking water after passing through all the treatment steps is a novel attitude that provided unique results. Additionally, microplastics down to the size of 1 µm were determined, which is rare.
The samples for analysing MPs were obtained from three drinking water treatment plants. All are located in urban areas of the Czech Republic and provide water for a considerable number of inhabitants, but they are supplied by diverse kinds of water bodies and differ in the treatment technology. MPs were analysed in terms of their abundance, size, shape and material composition. Microplastics were found in all water samples and their average abundance ranged from approximately 1500 to 3600 particles l-1 in raw water and from 340 to 630 particles l-1 in treated water, depending on the WTP. Thus, the decrease in the number of MPs after passing the treatment process was around 70-83%. Further, MPs smaller than 10 µm were the most plentiful in both raw and treated water samples, accounting for up to 95%. Majority of the MPs (> 70%) comprised of commonly utilized plastic materials such as PET (polyethylene terephthalate), PP (polypropylene) and PE (polyethylene).
Pivokonsky, M., Cermakova, L., Novotna, K., Peer, P., Cajthaml, T., Janda, V., (2018). Occurrence of microplastics in raw and treated drinking water. Science of The Total Environment 643, 1644-1651.