Should We Be Worried About Microplastics In Drinking Water?

There is growing concern related to microplastics and their widespread contamination in the environmental. The almost ubiquitous use of plastic materials in the modern world has led to extensive plastic waste, rubbish and debris making its way into the environment. Most plastics are extremely durable and will remain in the environment for generations. However, once discarded, the products we are familiar with, such as clothing, containers and bottles steadily breakdown to form plastic particles less than 5 mm in dimension. These microplastic particles eventually end up in the food chain, finally making their way into humans, with yet unknown health effects and consequences.

Microplastics are now everywhere

Plastics are a recent human invention with the earliest examples being produced at the end of the nineteenth century and commercial use only from the 1950s onwards. The low production costs and versatility of these substances has made them one of the most widely used materials. Plastic usage is growing rapidly with over half of all plastic material every produced having been made in just the last 25 years. Very little of this has been recycled (9%) or incinerated (12%). The remainder has been buried in landfill or released into the environment forming plastic pollution. Poor waste management has fuelled a surge in microplastics leading to them being found almost everywhere. Scientists have detected microplastics in meats, fruits and vegetables as well as sources of drinking water and bottled water.

Estimates on the ingestion of microplastics by humans exceed 120,000 particles per year, predominantly from air, food and drink. People who drink bottled water may be adding a further 90 000 of the smallest particles to their annual intake.

Microplastics and dementia  

A recent study looked at microplastics contamination of drinking water and its impact on the cognitive behaviour of mice. In less than a month the scientists found that microplastics had entered the brains of the mice, breaking through the blood-brain barrier. Once contaminated with microplastics, the mice started to show signs of mental decline similar to dementia. This new research highlights the potential impact on human health of microplastics in drinking water. However, like many other studies associated with microplastics in the laboratory or animals, these are difficult to generalise to humans and the associated risk remains uncertain. 

Drinking water and microplastics

Until recently there has been only a few studies that have directly looked at the amount and size of microplastics in drinking water. This is now changing quickly as concern for the health impacts of microplastics has motivated governments and regulators to act. In particular the California Senate Bill 1422 has now forced the state to adopt standards for testing microplastics in drinking water. This has led to interlaboratory studies to identifity the most effective methods for monitoring microplastics in water with dimensions down to 1 micron.

A recent study in the UK looked at 177 tap water samples from 13 cities and 85 plastic water bottle samples from 17 common brands.  Worryingly microplastics were found in every water sample from a range of water sources! The study found that while tap water samples on average had higher microplastic concentrations. Bottled water however had on average significantly smaller particle size than tap water. 

Smaller particle size maybe important for the blood-brain defences against microplastics. In the study on cognitive decline of mice contaminated with microplastics the particle sizes were between 0.1 and 2 microns. The current understanding of toxicity associated with microplastics suggests that size does matter and smaller microplastics will find it easier to pass through tissue layers and be absorbed through the stomach and lungs and enter deep into the body. Early studies now suggest that smaller particles, below 25 microns, can pass through biological barriers and accumulate in organs causing adverse effects. While larger particle sizes are less likely to have toxic effects since they are unable to pass through biological membranes. This work suggests that bottled water with an on average higher concentration of smaller microplastics, and maybe much worse for humans than previously thought.  

How toxic are microplastics

The most common plastic materials that contribute to tiny plastic particles are Poly Vinyl Chloride (PVC), Polyethylene Terephthalate (PET), Polystyrene (PS), and Polyethylene (PE). Other toxic chemicals you maybe familiar with such as PFAS (forever chemicals associated with nonstick cookware) and BPA are also found in microplastics as additives. These chemicals mimic natural hormones in the body leading to a range health conditions including problems with reproductive health.

As plastic particle size decreases it becomes more likely to pass through barriers such as the stomach walls or lungs and penetrate deeply into the body. Additionally, as the particle size decreases the surface area-to-volume ratio increases, which increases the likelihood of adsorbing toxic proteins and molecules that are then delivered directly to organs within the body. Chemical additives such as cadmium, lead and BPA in older plastics can also leach out of the microplastic particle once ingested.  

Plastics and microplastics can also form the perfect home for bacteria and biofilm forming organisms. While most of these are non-pathogenic some can include pathogens such as Pseudomonas aeruginosa, Legionella spp., non-tuberculosis Mycobacterium spp. and Naegleria fowleri. A recent report by the WHO has looked at the toxicity of microplastics and their ability to act as long-distance transporters for pathogens such as enteric viruses and protozoa. 

Filtering and removing microplastics.

Should you buy an expensive kitchen filter to remove microplastic pollution from drinking water? Recent research suggests that if you live in a hard water area there is a much more cost-effective solution. Simply boiling and pouring the water through a coffee filter can remove microplastic particles. The mineral-rich hard water forms limescale and crystalline structures that trap the microplastics. The chalky substance is calcium carbonate (CaCO₃) which forms in the kettle and acts as a natural filter for microplastics. In recent tests using drinking water with 300 milligrams of CaCO₃ per litre, boiling for 5 minutes removed 90% of microplastics. Even soft water samples demonstrated a positive effect associated with boiling water, which removed 25% of the microplastics. This research suggests that drinking boiled water can help reduce tiny particles being ingested. 

Testing for microplastics in food and water

There are now well established and widely used methods to detect microplastics in the environment. These techniques are optical microscopy, where the microplastic particles can be counted individually, categorised and their dimensions measured. This allows information on the colour and shape of the plastic fragments to be studied. To determine the chemical composition of the microplastic particle requires more sophisticated spectroscopic tools. One method collects infrared light over a large spectral range and then analyses the absorbed light using a mathematical technique known as Fourier analysis. This method of Fourier Transform Infrared Spectroscopy (FTIR microscopy for short) can correctly identify polymer types such as PET, PVC and PE down to micron size particles with better than 90% accuracy. Another method scatters laser light off the microplastic particle and analyses the characteristic shift in colour associated with a specific plastic type. This method of Raman microscopy is widely used in analytical chemistry laboratories around the world making it well suited to identifying the chemical composition of the microplastic.