The World Health Organization (WHO) has reviewed 50 studies that examine the presence of microplastics, particularly in drinking water. But the review has found that understanding the impact of these particles on human health continues to remain a challenge.
Microplastics enter freshwater environments in a number of ways, including surface run-off and wastewater effluent, as well as combined sewer overflows, industrial effluent, degraded plastic waste and atmospheric deposition.
“The lack of standard methods for sampling and analyzing microplastics in the environment means that comparisons across studies are difficult,” state the authors of WHO’s new microplastics report. “In addition, few studies were considered fully reliable. Nevertheless, some initial conclusions can be drawn,” they added.
The polymers most frequently detected in drinking water were polyethylene terephthalate (fibres for clothing and containers for food and fluids) and polypropylene (packaging and labelling).
The WHO report states that human health risks from microplastics in drinking water are a function of both hazard and exposure. It considers three primary forms: the particles themselves, which present a physical hazard; chemicals (unbound monomers, additives, and sorbed chemicals from the environment); and microorganisms that may attach and colonize on microplastics, known as biofilms.
“Although there is insufficient information to draw firm conclusions on the toxicity of nanoparticles, no reliable information suggests it is a concern,” the study’s authors state. “The fate, transport and health impacts of microplastics following ingestion is not well studied and no epidemiological or human studies on ingested microplastics have been identified,” WHO adds.
According to available data, wastewater treatment can effectively remove more than 90% of microplastics from wastewater, with the highest removals from tertiary treatment such as filtration. However, WHO states that approximately 67% of the population in low- and middle-income countries lack access to sewage connections and about 20% of household wastewater collected in sewers does not undergo at least secondary treatment.
The WHO report states there is a need to better understand microplastics occurrence throughout the water supply chain, using quality assured methods to determine the numbers, shapes, sizes, composition and sources of microplastics and to better characterize the effectiveness of water treatment.
The report also states that research is also needed to better understand the significance of treatment-related waste streams as contributors of microplastics to the environment.
With respect to potential health effects, the report states that quality-assured toxicological data are needed on the most common forms of plastic particles relevant for human health risk assessment. Further, a better understanding on the uptake and fate of microplastics and nanoplastics following ingestion is needed.