Microplastics in drinking water, WHO calls for risk assessment


Microplastic pollution in drinking water-both tap and bottled-is well established. And there is an urgent need to assess the risk to public health. The appeal of the World Health Organization (WHO), in the report Microplastics in Drinking Water.(1)

Microplastics in water, still few studies

Microplastics-as revealed in a series of research studies-are now widespread in water and in the atmosphere. They have thus become part of our diet, including through MOCAs (food contact materials). With a total estimated individual intake of about 5 grams per week.

TheWHO/WHO (World Health Organization) report highlights the existence and timeliness of a food security problem. related to contamination of water resources by particles of plastic materials. Highlighting at the same time the paucity of available scientific data, which to date does not allow for an appropriate risk assessment, the urgency of which, moreover, is pointed out.

The systematic review of available scientific literature identified 50 research studies on the presence and amount of microplastics in freshwater, drinking water and wastewater. (2) However, these studies are not sufficient to examine the problem in its true magnitude. All the more so in the absence of shared standards for sampling and analysis of contaminants in the environment and food. It is therefore difficult to make statistically relevant comparisons.

Only nine studies have looked at microplastics in drinking water. Fragments and fibers are the predominant forms, polyethylene terephthalate and polypropylene the most frequent polymers. The maximum concentration detected so far is 104 particles per liter; their minimum size is 1 nanometer.

Microplastics in water, what consequences

There are several potential hazards associated with contamination of drinking water with microplastics. The physical risk of accumulation in tissues and organs, the chemical risk that can result from particle toxicity, and the microbiological risk related to bacteria.

The physical risk of microplastic accumulation in the body is considered of no concern. Purely theoretical, which WHO itself points out lacks any scientific support. Based solely on a hypothesis that particles larger than 150 micrometers in size could be expelled through digestion. Hence the improbability of their absorption would be inferred.

Conversely, the risk of accumulation of nanoparticles (measuring less than 0.1 μm, 100 nm) in liver and kidney, through the lymphatic system and blood is known. As has already emerged in relation to titanium dioxide, the nanometer mineral used as a food coloring (E171) and a component of cosmetics. However, according to WHO, the limited number of toxicological studies conducted on animals prevents firm conclusions. And the damage so far observed on animals following microplastic administration has occurred at very high doses, not comparable to those found in drinking water.

Chemical risk is related to the biodegradation of materials, as well as the presence of processing residues. As well as to substances added in plastics that are known to be harmful, such as phthalates and flame retardants. Again, however, based on the scant data available, the WHO considers the current population exposure to microplastics in drinking water to be ‘not of concern’.

The risk related to microorganisms growing in drinking water pipes is focused on bacterial colonies that form so-called biofilms. In fact, some of them include pathogenic microorganisms, such as Pseudomonas aeruginosa, Legionella spp. and Naegleria fowleri. And plastic is an ideal surface for their rooting and growth. Thus, some studies indicate the possibility that microplastics may allow long-distance transport of pathogens in fresh water and increase the transfer of antimicrobial-resistant genes among microorganisms. Once again, however, the WHO does not consider the available studies suitable for establishing an effective link between risks from biofilms and microplastics in drinking water.

Microplastics, how they end up in the glass

Microplastics are ubiquitous, as mentioned in the introduction. Having been detected in marine and wastewater, fresh water, food, air and drinking water, both bottled and piped.

Microplastics found in drinking water can come from erosion of plastic parts of water treatment and distribution systems. For bottled mineral water, however, the WHO lists bottles and packaging caps as possible sources.

Water treatment systems are in theory an effective filter for retaining plastic fragments. Wastewater plants should theoretically remove up to 90 percent of microplastics. While those for drinking water should retain particles smaller than a micrometer through coagulation, flocculation, sedimentation/flotation and filtration processes.

The most advanced systems contemplate ultrafiltration, capable of removing even nanoscale particles. But 67 percent of the population in low- and middle-income countries lack access to basic water services, and 20 percent of domestic wastewater collected in sewers does not undergo at least secondary treatment, WHO points out.

WHO’s conclusions.

The presence of pathogens in drinking water remains the most significant risk to human health, along with the risks of chemical contamination. In contrast, routine monitoring of microplastics is not recommended by the WHO, as there is no evidence to indicate a human health concern.

Evidence must still be sought, the WHO cautions. That calls for researchers to undertake work on health risks and investigative studies to better understand the sources and presence of microplastics in freshwater and drinking water, the effectiveness of different treatment processes, and the potential return of microplastics to the environment including through the application of sludge to farmland.

Little evidence, one serious indication of risk.


(1) World Health Organization. (2019). Microplastics in drinking-water. ISBN 978-92-4-151619-8, https://apps.who.int/iris/bitstream/handle/10665/326499/9789241516198-eng.pdf?ua=1

(2) Albert A. Koelmans, Nur Hazimah Mohamed Nor, Enya Hermsen, Merel Kooi, Svenja M. Mintenig, Jennifer De Franced. Microplastics in freshwaters and drinking water: Critical review and assessment of data quality. Water Res. 2019 https://doi.org/10.1016/j.watres.2019.02.054

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Professional journalist since January 1995, he has worked for newspapers (Il Messaggero, Paese Sera, La Stampa) and periodicals (NumeroUno, Il Salvagente). She is the author of journalistic surveys on food, she has published the book "Reading labels to know what we eat".