Microplastics in drinking water not a health risk for now as WHO study fails to find conclusive evidence
Microplastics are increasingly found in drinking water, but there is not enough evidence yet to conclude that they pose a serious risk to human health at current levels.
This is the conclusion of the first report on microplastics in drinking water by the World Health Organization (WHO).
However, the WHO experts warn that the report is based on very limited and sometimes even unreliable data/information and says there is an urgent need to know more about the health impact on microplastics as they are present everywhere.
“Based on the limited information we have, microplastics in drinking water do not appear to pose a health risk at current levels. But we need to find out more. We also need to stop the rise in plastic pollution worldwide. We urgently need to know more about the health impact of microplastics because they are everywhere - including in our drinking water,” says Dr. Maria Neira, Director, Department of Public Health, Environment and Social Determinants of Health, at WHO.
Given that humans can be exposed to microplastics through a variety of environmental media, the WHO has initiated a broader assessment of microplastics in the environment. A future report will characterize the potential human health risks due to total microplastic exposure from the environment, including through food and air.
Humans routinely ingest many different kinds of particles consisting of a variety of substances. The researchers say that particle toxicity depends on a variety of physical properties, including size, surface area, shape and surface characteristics, as well as the chemical composition of the microplastic particle.
However, according to the WHO analysis, which summarizes the latest knowledge on microplastics in drinking water, microplastics larger than 150 micrometers are not likely to be absorbed in the human body. Further, uptake of smaller particles is expected to be limited, although absorption and distribution of very small microplastic particles, including nano plastics, may be higher. However, researchers say that the database is extremely limited and findings demonstrating uptake in animal studies occurred under extremely high exposures that would not happen in drinking water.
Based on this limited body of evidence, firm conclusions on the risk associated with ingestion of microplastic particles through drinking water “cannot yet be determined,” the researchers say. They add that however, at this point, no data suggests “overt health concerns” associated with exposure to microplastic particles through drinking water.
Why this study?
While there is no scientifically-agreed definition of microplastics, they are frequently defined as plastic particles less than 5 mm in length.
Over the past few years, several studies have reported the presence of microplastics in treated tap and bottled water, raising questions and concerns about the impact that microplastics in drinking water might have on human health.
Accordingly, the WHO report critically examines the evidence related to the occurrence of microplastics in the water cycle - including both tap and bottled drinking water and its sources - the potential health impacts from microplastic exposure and the removal of microplastics during wastewater and drinking water treatment.
Microplastics are ubiquitous in the environment and have been detected in marine water, wastewater, freshwater, food, air, and drinking water, both bottled and tap water.
They enter drinking water sources or freshwater environments in multiple ways: primarily from surface run-off and wastewater effluent (both treated and untreated), but also from combined sewer overflows, industrial effluent, degraded plastic waste, and atmospheric deposition.
However, there are limited data to quantify the contribution of each the different inputs and their upstream sources.
The insufficient evidence indicates that some microplastics found in drinking water may come from treatment and distribution systems for tap water and/or bottling of bottled water.
Plastic bottles and caps that are used in bottled water may also be sources of microplastics in drinking water.
“A recent systematic review of the literature identified 50 studies detecting microplastics in freshwater, drinking water, or wastewater. The lack of standard methods for sampling and analyzing microplastics in the environment means that comparisons across studies are difficult. In addition, few studies were considered fully reliable. Nevertheless, some initial conclusions can be drawn,” says the report.
It warns, “A WHO-commissioned study concluded that most of these studies (on microplastics) are not fully reliable because their methods lacked sufficient quality control. Results should, therefore, be interpreted with caution.”
What did the experts find?
In freshwater studies, reported microplastic particle counts ranged from around 0 to 1000 particles/liter.
“Only nine studies were identified that measured microplastics in drinking water: these studies reported particle counts in individual samples from 0 to 10,000 particles/liter,” says the study.
According to the WHO experts, a comparison of the data between freshwater and drinking water studies should not be made because in most cases freshwater studies targeted larger particles, using filter sizes that were an order of magnitude larger than those used in drinking water studies.
Stating that the human health risk from microplastics in drinking water is a function of both hazard and exposure, the researchers say that potential hazards associated with microplastics come in three 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.
“Based on the limited evidence available, chemicals and microbial pathogens associated with microplastics in drinking water pose a low concern for human health. Although there is insufficient information to draw firm conclusions on the toxicity of plastic particles and particularly the nano-size particle, no reliable information suggests it is a concern,” the report states.
The researchers, however, caution that irrespective of whether there are any risks to human health from ingestion of microplastics in drinking water, there is a need to improve management of plastics and reduce plastic pollution to protect the environment and human well-being.
Poorly managed plastic can contribute to sanitation-related risks and air pollution, and impact tourism and overall quality of life. If plastic emissions into the environment continue at current rates, there may be widespread risks associated with microplastics to aquatic ecosystems within a century, with potentially concurrent increases in human exposure, they add.
The world plastic production has increased roughly exponentially since large-scale production first began in the 1950s, and considering the estimated worldwide population growth rate and current consumption and waste habits, plastic production is predicted to double by 2025 and more than triple by 2050, says the report.
“In response to concerns about the impact of plastic and microplastic pollution, public engagement and political commitment have increased. More than 60 countries are already taxing or banning single-use plastics, primarily plastic bags,” it states.
What can be done?
Wastewater and drinking water treatment systems - where they exist and are optimized - are considered highly effective in removing particles of similar characteristics and sizes as microplastics.
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.
Stating that routine monitoring of microplastics in drinking water is not recommended at this time, the WHO experts recommend that water suppliers and regulators should continue to prioritize removing microbial pathogens and chemicals from drinking water that are known significant risks to human health.
“As part of water safety planning, water suppliers should ensure that control measures are effective, including optimizing water treatment processes for particle removal and microbial safety, which will incidentally improve the removal of microplastic particles. Routine monitoring of microplastics in drinking water is not necessary at this time,” the report says.
The team says to better assess the human health risks and inform management actions, researchers should undertake targeted, well-designed, and quality-controlled investigative studies.
These studies, they say, should facilitate a better understanding of the occurrence of microplastics in the water cycle and in drinking water throughout the water supply chain, the sources of microplastic pollution and the uptake, fate and health effects of microplastics under relevant exposure scenarios.
Measures should also be taken to better manage plastics and reduce the use of plastics where possible, to minimize plastic and microplastic pollution, state the recommendations.
Research gaps must be filled
A key message that the researchers drive through this study is that not much is known or understood about the consequences of exposure to microplastics and their potential impacts on human health.
To better assess human health risks and inform management actions, a number of research gaps need to be filled, say the experts.
With respect to exposure, there is a need to understand microplastics occurrence throughout the water supply chain better, using “quality-assured methods to determine the numbers, shapes, sizes, composition, and sources of microplastics” and to better characterize the effectiveness of water treatment.
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, says the team, ‘quality-assured toxicological data’ are needed on the most common forms of plastic particles relevant for human health risk assessment.
Further, a better understanding of the uptake and fate of microplastics and nanoplastics following ingestion is needed.
“Finally, given that humans can be exposed to microplastics through a variety of environmental media, including food and air, a better understanding of overall exposure to microplastics from the broader environment is needed,” the report says.