Microplastics: A hidden threat in rivers, lakes, oceans – and drinking water

Whether they show up in the ocean or coming out of the tap, microplastics raise serious environmental and toxicological concerns – and they’re becoming a real-world test for healthcare, environmental protection, wastewater treatment, major industries, and marine ecosystems. One problem is that measurement methods still vary widely: studies use different size ranges and detection limits, so reported concentrations can swing from “almost none” to hundreds of particles per liter depending on the method used.

Many international bodies still rate the immediate health risk from microplastics as low. Even so, momentum is building for clearer regulation and standardized measurement. Public concern is rising too, and people increasingly expect transparency and meaningful action. For water utilities, hospitals, and pharmaceutical and food manufacturers, the implication is straightforward: decisions based on inconsistent monitoring data – or outdated guidance – create significant operational and reputational risk. Water-treatment investments need to meet today’s compliance expectations and remain consistently resilient as standards tighten – while also mitigating reputational risk.

Microplastics are solid plastic particles smaller than five millimeters. They occur in soil, air, rivers and lakes, and the ocean as fragments, fibers, and pellets. They’re usually grouped into two categories: Primary microplastics are intentionally produced in particle form – such as pellets, granules, or microbeads – for use within products and industrial processes. Secondary microplastics form when larger plastic items break down over time and produce smaller particles that enter the environment.¹

Other major sources include abrasion (especially from tires and synthetic textiles) and industrial losses. Eventually, these particles reach rivers and lakes, which often supply raw water for drinking-water production. The risk isn’t only that organisms can ingest these particles. Microplastics can also carry additives and pollutants, and the long-term effects on ecosystems and human health are still not fully understood. That’s why institutions such as the World Health Organization (WHO) continue to call for more research.

People are exposed to microplastics mainly through food (including fish and seafood), drinking water, and inhalation of airborne particles. Studies have detected particles in human tissues, but the evidence linking exposure to specific diseases is still limited. Experimental findings suggest possible effects^2,3 such as inflammation, oxidative stress, and changes to the gut microbiome, but clear clinical outcomes have not yet been established⁴.

Microplastics can also transport chemical additives and other contaminants (for example plasticizers or persistent organic pollutants), some of which may affect hormonal systems⁵ or other biological functions or even be toxic (for the brain or the colon)⁶. Per- and polyfluoroalkyl substances (PFAS) are persistent synthetic chemicals used since the 1950s for water-, grease-, and stain-resistant applications that can also accumulate in the human body. Combined exposure is an additional concern: early evidence suggests PFAS and microplastics together could produce stronger effects than either one alone, though the real-world implications are still uncertain.

In rivers, lakes, and oceans, microplastics are eaten by plankton, mussels, and fish⁷ and can move through food webs. Beyond physical irritation or blockage (blood–brain barrier), the particles may introduce heavy metals and organic contaminants that can affect growth and reproduction in some species. People can also ingest microplastics indirectly through seafood.

A further concern is particle size. Smaller microplastics – and especially nanoplastics – may be able to cross biological barriers and enter tissues. Once there, removal is difficult and may be impossible. Plants can take up very small particles through their roots, potentially affecting nutrient uptake and physiological processes⁸. Over time, this could disrupt ecosystems in dramatic ways that go far beyond the highly visible plastic pollution at the ocean’s surface.

While the threat landscape for surface waters and drinking water is fairly clear, groundwater is harder to assess. Microplastics do enter soils through sewage sludge, agriculture, and infiltrating surface water, but there is still not enough research on how many particles actually make it down into deeper aquifers. Soil filtration processes trap some of the particles and reduce contamination; at the same time, early studies¹⁴ suggest that smaller micro- and nanoplastic particles may still reach groundwater under certain conditions. Overall, this pathway is considered a plausible risk, but the actual level of contamination – and its long-term significance for drinking-water resources – remains highly uncertain.