Microplastics pose minimal health threat, but more effective studies are needed, stresses WHO

22 Aug 2019 --- The long-awaited findings of the World Health Organization’s (WHO) assessment of microplastics in the environment have been published, with the organization indicating that the impact on human health appears to be minimal at current levels. At the same time, WHO has stressed that it was working from “limited information” and that there is a pressing need to establish more standardized methods for measuring microplastic particles in water; more studies on the sources and occurrence of microplastics in freshwater; and the efficacy of different treatment processes.

According to WHO’s 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 and uptake of smaller particles is expected to be limited. Absorption and distribution of very small microplastic particles, including in the nano-size range may, however, be higher, although “the data is extremely limited.”

The WHO assessment was launched in response to a study published by New Orb Media in May last year, which found potentially harmful plastic particles in the water bottles of 11 leading global brands, including Dasani (Coca-Cola), Epura (PepsiCo), Aqua (Danone) and Nestlé Pure Life and San Pellegrino (Nestlé). Exclusive testing was conducted on more than 250 bottles from nine different countries, with 93 percent found to have contained plastic debris the size of the width of a human hair, including polypropylene, nylon, and polyethylene terephthalate (PET).

Although there is insufficient information to draw firm conclusions on the toxicity related to the physical hazard of plastic particles, no reliable information suggests it is a concern. “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. “Based on the limited information we have, microplastics in drinking water don’t 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.”

The potential hazards associated with microplastics come in three forms: physical particles, chemicals and microbial pathogens as part of biofilms. Based on the limited evidence available, chemicals and biofilms associated with microplastics in drinking-water pose a low concern for human health, according to WHO. Although there is insufficient information to draw firm conclusions on the toxicity related to the physical hazard of plastic particles, particularly for the nano-size particles, no reliable information suggests it is a concern. 

Microplastics, everywhere
Alistair Boxall, Professor in Environmental Science at the University of York, UK, tells PackagingInsights that he is not surprised by the findings. “We know microplastics are everywhere, even in the arctic, so I think it is inevitable that they will find their way into drinking water and food. Recent work has also detected microplastics in human feces showing that we are exposed,” he says.

In October of last year, Boxall published an investigation into the published literature on microplastics, indicating “significant gaps in our understanding of the effects” of the less than 5mm size plastic particles on the environment. Boxall and study co-author, Emily Burns, called for “better quality and more holistic monitoring studies alongside more environmentally realistic effects studies on the particle sizes and material types that are actually in the environment.”

“There is a very large amount of research on microplastics, but most of this to date has focused on marine systems. Only recently have scientists started to look at other systems such as rivers, soils and drinking water. One of the big challenges we have is with how to analyze these things. Current methods only get down to a few microns in size so we are probably missing all the smaller particles, for example, nanoplastics that are likely to be present and are also of greater toxicological concern,” Boxall explains.

WHO is calling for a further assessment of microplastics in the environment and their potential impacts on human health, following its release of an analysis of current research related to microplastics in drinking water. The organization also calls for a reduction in plastic pollution to benefit the environment and reduce human exposure.

This week, plastic fibers were identified in rainwater samples from the rural Rocky Mountain National Park, US, further highlighting the ubiquitous nature of plastic fibers and particles.

Microplastics in drinking water: How does it happen?
Microplastics may enter drinking water sources in several ways: from surface run-off (for example, after a rain event), to wastewater effluent (both treated and untreated), combined sewer overflows, industrial effluent, degraded plastic waste and atmospheric deposition, WHO explains. Surface run-off and wastewater effluent are recognized as the two main sources, but better data are required to quantify the sources and associate them with more specific plastic waste streams.

On the issue of how microplastics are entering bottled water, Boxall believes that it is still “a bit of an unknown. It will depend on where the source water is obtained and the packaging process,” he says. “For bottled waters, some particles could be slipping through the treatment process used on the source water and there might be inputs from the packaging process and the bottle itself.”Microplastics are ubiquitous in the environment and have been detected in a broad range of concentrations in marine water, wastewater, fresh water, food, air and drinking water, both bottled and tap water. 

In the opinion of Jeroen Dagevos, Head of Programs at the Plastic Soup Foundation, plastic bottles and caps that are used in bottled water may indeed be a source of microplastics in drinking water. “PET and PP were the most found plastics in bottled water and the bottle and cap are made of these,” he tells PackagingInsights.

“I suspect though that, in Europe at least, drinking water might not be the main contributor to what gets into the body but food and airborne exposure (for example, when you open the door of a tumble drier you will likely get a dose) are probably more important. In regions with poorer drinking water treatment it could be a much more important exposure route,” Boxall adds.

Where do we go from here?
WHO recommends drinking-water suppliers and regulators prioritize removing microbial pathogens and chemicals that are known risks to human health, such as those causing deadly diarrhoeal diseases. This has a double advantage: wastewater and drinking water treatment systems that treat fecal content and chemicals are also effective in removing microplastics.

Wastewater treatment can remove more than 90 percent of microplastics from wastewater, with the highest removal coming from tertiary treatment such as filtration, WHO suggests. Conventional drinking water treatment can remove particles smaller than a micrometer. A significant proportion of the global population currently does not benefit from adequate water and sewage treatment. By addressing the problem of human exposure to faecally contaminated water, communities can simultaneously address the concern related to microplastics.

Meanwhile, WHO is calling for significant improvement in the quality control of future microplastic studies after its commissioned study concluded that present studies are not fully reliable. Results should therefore be interpreted with caution. For example, in two drinking-water studies and for a subset of smaller particles in a third study, no spectroscopic analysis was conducted to confirm that the particles identified were plastic. Four of the 52 studies that scored highest for quality were published in 2017 and 2018, indicating some improvements in quality control.

The quality control areas requiring the most improvement include sample treatment, polymer identification, laboratory preparation, clean air conditions and positive controls.

In addition to improved quality control on microplastic studies, WHO is also calling for a crackdown on plastic pollution. Irrespective of any human health risks posed by exposure to microplastics in drinking water, measures should be taken by policymakers and the public to better manage plastics and reduce the use of plastics where possible, to minimize plastics released into the environment because these actions can confer other benefits to the environment and human well-being, WHO stresses.

How can a reduction in plastic pollution be achieved?
According to Boxall, the simple answer is to phase out single-use plastics and develop improved recycling systems for multi-use plastics. “We should also look to develop ways in which can catch particles at source, for example, filters on washing machines to collect particles generated by clothing and filtration systems on highways to remove tire particles.”Plastic bottles and caps that are used in bottled water may be sources of microplastics in drinking water. 

In May, the Council of the EU officially adopted measures proposed by the European Commission to tackle marine litter by banning the 10 single-use products most commonly found on European beaches. This includes cotton bud sticks, cutlery, plates, straws and stirrers and also incorporates abandoned fishing gear and oxo-degradable plastics. The Member States will now have two years to transpose the legislation into their national law.

“We could also introduce tertiary treatments on wastewater treatment plants – this would not only remove the microplastics but also the many other micropollutants that occur in the environment that are probably more toxic,” Boxall explains.

“There is talk about moving towards biodegradable plastics – while this will help exposure in the oceans, I am not convinced that it will help rivers and drinking waters – we will just see other polymers in our drinking water,” he adds.

Dagevos also highlights the need to not add microplastic to products intentionally. “This is still happening with, for example, cosmetics, cleaning agents and agricultural products.”

“We need to avoid the degradation of plastics into the environment. Microfibers from clothes are a big source – on average 9 million fibers per 5 kg wash. Let’s develop better yarn, pre-wash and use protecting coatings,” he advises.

Given that humans can be exposed to microplastics through a variety of environmental media, 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.

By Joshua Poole