Plastic in drinking water
Water is an essential nutrient that plays vital roles in our body. Unlike other nutrients, we can barely store it, so we are forced to continually replenish it through liquid consumption. Developed societies have managed to supply the population with quality water through infrastructures for collection, treatment, and distribution. However, differences in quality and the occasional presence of contaminants call into question the effectiveness of existing measures, quickly jump out to the media and generate public concern. In this context, references to drinking water contamination by metals, nitrates from agricultural activities, or persistent chemical compounds such as perfluorinated substances are common. Microplastics could not be an exception, and therefore, the European Union included them in its Directive 2020/2184 on the quality of water intended for human consumption through a watch list mechanism, along with other emerging contaminants such as endocrine disruptors.
It is a well-known fact that microplastics have been detected in both tap water and bottled water, which inevitably raises concerns about their impact on human health. Our own research has revealed their presence in both tap water and bottled water. An obvious question is: where do all these plastics that end up in drinking water come from? The answer is that we ourselves are the ones who spread them into the environment. Drinking water treatment plants draw water from rivers, reservoirs, or aquifers, and process it through physical and chemical treatments such as filtration, sedimentation, and disinfection in order to remove impurities and microorganisms. Once treated, the water is distributed through pipe networks to homes. However, waterways receive numerous inputs of plastics from a wide range of sources. Industrial and agricultural activities, or the fragmentation of objects during their use, such as synthetic textiles or car tires, produce plastics that end up in the rivers that supply drinking water treatment plants, and into which wastewater treatment plants also discharge. In this way, a kind of plastic cycle is generated, facilitated by the fact that neither drinking water treatment plants nor wastewater treatment plants are designed to fully eliminate the small plastic particles carried by water.
Bottled water plants generally draw water from springs or aquifers, which are presumably less contaminated than surface waters. However, neither springs nor, of course, bottling facilities are free from plastic contamination, including that which occurs through atmospheric deposition, which is ubiquitous. Furthermore, it is a well-established fact that the vast majority (over 90%) of bottled water sold worldwide is distributed in plastic containers, especially in bottles made of polyethylene terephthalate, commonly abbreviated as PET. These containers are lightweight and inexpensive, allowing significant fuel savings during transport and consequently reducing greenhouse gas emissions compared to other types of packaging. They are also moderately recyclable; but ultimately, they are still plastic. It is not surprising that the majority of the plastic found in PET bottles is PET.
The World Health Organization (WHO), in its report Microplastics in drinking water, states that although current levels of microplastics in drinking water do not appear to pose a significant risk to human health, the available evidence is limited. Some studies suggest that ingestion of microplastics could be associated with inflammation and other adverse effects on internal organs, although these findings are not yet conclusive since they entirely refer to acute exposures at very high concentrations and almost always to polymers that are not representative of the real contaminants. There is an almost complete lack of data on realistic and long-term exposures, making it impossible to conduct a minimally reliable risk assessment. However, the precautionary principle advises against minimizing risks that are difficult to quantify. In response, the Commission, through Delegated Decision (EU) 2024/1441, has established a reference methodology for measuring microplastics in drinking water based on vibrational spectroscopy (infrared or Raman microscopy).
Going back to the data, which were partly discussed in a previous post, researchers from Columbia University used a nonlinear Raman technique to estimate a concentration on the order of hundreds of thousands of plastic particles per litre of bottled water, a striking figure explained by the small size of the detected particles, the vast majority of which ware below one micron. Expressed in terms of mass, the concentration was about 10 ng/L. Our data for bottled water indicated a concentration of plastic particles smaller than 100 µm of 176 ng/L and a total of 1.61 µg/L. Using the fractal fragmentation rule with dimension D = 3, our 176 ng/L would correspond to about 2 ng/L of particles smaller than 1 µm, compatible with the measurement (carried out using a much smaller sample) by the Columbia group. In tap water, the concentration measured by us was 45.5 ng/L, about 35 times lower than that of bottled water. Other authors reported reasonably comparable concentrations, considering differences in particle size and the uncertainty of this kind of studies. For instance, a concentration of 0.77 µg/L (< 1 mm) was measured in drinking water treatment plants in Harbin, China; in tap water samples in Barcelona the concentrations reached up to 9.7 µg/L (0.70-20 µm); and in PET bottles from a supermarket in France the concentration of plastic was 28 ng/L. If, again for precaution, we take a high value of 10 µg/L and assume a consumption of 2 litres of water per person per day, the estimated daily intake (EDI) would be in the range of 0.30-1.25 µg kg-1 day-1, a value similar to that of other contaminants such as heavy metals calculated, for example, from WHO guideline values. In other words, a person drinking 2 litres of water a day would take about 3 years to ingest as much plastic as contained in a single pellet spilled off by Toconao cargo ship in 2024 and nearly 700 years to ingest the famous credit card we supposedly consumed every week.
In short, regardless of the low exposure rate and the uncertainty of the potential health risks derived from exposure to plastic particles, measures must be taken to better manage plastics and reduce their uncontrolled spread in the environment. Risky or not risk, when we turn on the tap or open a bottle of water, we expect to find only water.