Microplastics are tiny plastic fragments that are found throughout the environment, including in soil and bodies of water. Microplastics are often defined as being between 0.1 and 5000 µm (micrometers) in length - somewhere between the size of the SARS-CoV-2 virus, and the diameter of a typical drinking straw - although there is no uniform definition. They can vary widely in shape, size, and chemical composition, as illustrated here by these comparable items.
Polyethylene (PE), polybutylene succinate (PBS), and polyvinyl chloride (PVC) are the most common microplastics. They are classified as either primary or secondary microplastics. Primary microplastics are manufactured below 5000 µm (5mm) in size for use mostly as industrial abrasives or in cosmetics. These account for less than 0.1% of total plastic production, as per the European Chemicals Agency (2019) and Plastics Europe (2018).
Secondary microplastics are formed by the breaking up of larger pieces when exposed to UV radiation (from the sun), high temperatures, and weathering in the environment. This was confirmed in independent studies in 2014 by Professor Johnny Gasperi of Université Paris-Est Créteil, and by Professor David Morritt of the School of Biological Sciences at Royal Holloway University of London. This infographic shows the different paths for microplastics to enter the environment and was assembled by the team from China’s Northwest University in the iGEM synthetic biology competition.
Microplastics in water may threaten animal and human health by entering the food chain or transporting concentrated contaminants in aquatic environments.Professor Cinzia Corinaldesi, an environmental scientist at the Polytechnic University of Marche, Italy studied the harmful biological effects of microplastics on corals. These microplastics caused tissue abrasions leading to bacterial infections, impairing mucus production, and could even lead to death. The corals exposed to high concentrations of microplastics incurred tissue damage which was 6.5 times that of corals that were not exposed to microplastics or had ingested low concentrations of microplastic after a period of 14 days.
Other studies cited showednegative impacts at molecular, cellular, and population levels on fish, larger marine creatures, and plankton. Disturbances in genetic functions, reproduction, and feeding were identified.
For humans, while there is an ongoing debate, drinking water containing microplastics or eating contaminated seafood may pose health threats. For example, the Woods Hole Oceanographic Institution found that certain microplastics in water such as polychlorinated biphenyls (PCBs) are linked to cancer.
A detailed review of earlier studies authored by Claudia Campanale and others at the Water Research Institute of the Italian National Research Council showed that microplastics under 10 micrometers could enter the fluid around the brain and other organs such as the liver, kidneys, and placenta.
As a relatively new area of research, there is uncertainty regarding the level of harm microplastics pose to human health. The latest research by the World Health Organization (WHO) suggests that many studies may be overestimating the health impacts on humans and that microplastics in water are likely to have a minimal effect when properly filtered out in Water Treatment Plants.
The effects and routes that microplastics could take within the body are not well understood. Further research into potential harmful effects on humans and the environment is critical. As shown in this chart, a 2020 risk assessment report by the European Chemicals Agency forecasts that European emission of microplastics could exceed 1.6 million tonnes per annum if proposed restrictions are not put into place.
There are five main water types that have microplastics.
Bottled water (drinking water)
Microplastics in each type have unique issues.
1. Tap Water
Tap Water is sourced from a local authority’s water system and is available in private and public buildings as well as some outdoor locations. It can come from any available source including groundwater aquifers, reservoirs, lakes, rivers, or desalinated seawater. Natural sources tend to be of higher initial quality, but all sources are usually filtered and treated to some degree before entering the system for general usage.
How much microplastic is in tap water? In a review of scientific studies by Professor Albert A. Koelmans of Wageningen University in the Netherlands, tap water samples were found to contain between 0.1 to 100 thousand microplastic particles per thousand liters.
This huge range is hard to generalize about, but the amount of plastic manufactured and used in a local area is likely a key factor in microplastic concentrations. As are potential transportation routes into an area such as rivers. Once microplastics have entered nature, they will inevitably enter the tap water system.
While municipal water treatment systems reduce the amount of microplastics to minimal levels, it is rare that they can entirely eliminate them. Even after being treated, water may pass through areas where microplastics can enter the system before reaching the consumer’s tap.
Potential harms and dangers from drinking tap water with microplastics include toxic effects to the digestive tract, links to serious illness such as cancer, a compromised immune system, or infiltration of the blood-brain barrier resulting in neurological complications. When washing or scrubbing, smaller microplastics in tap water could be absorbed through the skin.
2. Bottled Water (Drinking Water)
The US Food and Drug Administration (FDA) defines bottled drinking water as water “intended for human consumption, sealed in containers with no added ingredients except safe and suitable antimicrobials and fluoride within limits”.
How much microplastic is in bottled water? With thousands of bottled water brands around the world from different sources and with different filtration and manufacturing processes, it is not possible to draw a firm conclusion on the amount of microplastics in the category as a whole. hypotheses that bottled water is unlikely to contain microplastics have been repeatedly shown to be incorrect.
Professor Albert A. Koelmans from Wageningen University found that microplastics in the bottled water they sampled varied widely in concentration from 0.01 to 100 thousand microplastic particles per thousand liters. Even in a limited sample range, this variation may be partly from the bottling processes themselves or the use of plastic caps.
In Canada, Dr. Kieran D Cox of the Department of Biology at the University of Victoria found the concentration of microplastics in bottled water brands they sampled to be 22 times higher than tap water.
While research on microplastics in bottled water remains limited due to the wide array of waters that have to be tested to draw clearer conclusions, thus far the research has shown bottled water tends to have higher concentrations than tap water.
But even this conclusion should be taken with caution as bottled water studies tend to measure for smaller particles than tap water studies. This means that the methodology is almost certain to show higher concentrations in bottled water than tap water which may not be correct if the same size particles are tested for.
Two of the main inputs of microplastics into freshwater are surface run-off (when plastic has accumulated around water bodies) and wastewater effluent (plastic present in used water), as illustrated by the following schematic produced by the World Health Organization (WHO) for their 2019 report, Microplastics in Drinking-Water.
Even deposits in the air can add to contamination in water sources. Bottled water utilizing natural sources can then be contaminated by the microplastics, especially if sufficient filtration is not utilized.
Presuming the studies pointing to the harmful effects of microplastics are correct, the tendency towards higher concentrations of microplastics in bottled water suggests a greater risk of health effects. But it must be reiterated that the methodologies between bottled and tap water studies have not matched, and the range of results have been extremely wide and inconclusive.
Regardless of the ultimate answer research finds, a bottled water brand using a well-protected source (such as iceberg water preserved long before plastics existed) and clean bottling processes are most likely to be among those found to have no microplastic content.
3. Marine Water
The Georgia Department of Natural Resources defines Marine Water as water from the sea or ocean having high salt content. Besides the open ocean, marine water can be found in the bilge water of ships.
How much microplastic is in marine water? A citizen science study known as the Global Microplastics Initiative published a report in the journal Environmental Pollution in 2018 where they showed that 90% of 1393 ocean samples from around the world had microplastics, with an average concentration of 118 particles per liter. 91% were microfibers from plastic elements in fabrics. Their measurements at different locations are shown on the map below.
Open ocean samples consistently had higher average concentrations (179 per liter) than coastal regions (59 per liter). The polar regions had the highest concentrations, with the Arctic averaging 313 particles per liter and the Southern oceans 154.
There was significant variation in the Arctic, with Canada and Alaska at the higher end of the range, while Svalbard samples had just 0 to 6 particles per liter. The Atlantic was still above average at 134 microplastic particles per liter, followed by the Pacific at 70 per liter and the Indian Ocean at 42.
Large plastic debris originating from urban environments regularly enters freshwater systems according to the 2014 studies by Professor Gasperi and Professor Morritt. According to Vivian S. Lin of the Institute of Biogeochemistry in Zurich, Switzerland, microplastics enter the environment directly via waste streams that include personal care products, textiles with synthetic fibers (often detached in washing machines), and cleaning agents. From there they can flow into the ocean environment. Discarded plastic fishing nets such as this one erode into microplastics over time.
Microplastics in water can have negative health effects on wildlife and can contribute to the transport of toxins and contamination of the food chain. According to Dr. Lin, they can enter at the bottom of the food chain when ingested by algae, bacteria, and plankton where they leach toxins that damage development and threaten survival. From there the damage moves up the food chain, including via reduced food intake and reproductive success for crustaceans in the middle of the food web as seen in research by Matthew Cole of the UK’s University of Exeter and colleagues.
Another example comes from Dr. Mark A Browne and colleagues from the School of Marine Science & Engineering, Plymouth University and the National Center for Ecological Analysis & Synthesis, University of California, Santa Barbara who noted that lugworms were found to have greater difficulty creating sediment burrows after microplastic ingestion.
Microplastics in marine water are ingested by humans via seafood. Key concerns to human health, in this case, are enhanced inflammatory response, the toxicity of plastic particles, contamination due to adsorbed chemical pollutants, and a disruption in the digestive system. Though these impacts are yet to be fully substantiated.
4. Waste Water
Wastewater is used water and can have human waste, food scraps, oils, soaps, fertilizers, or industrial chemicals present in it.
How much microplastic is in wastewater? A study by Daniel Sol et al. at the Department of Chemical and Environmental Engineering of the University of Oviedo in Spain found that wastewater treatment plants they tested in the United States had between 83.3 and 147 microplastics particles/L when untreated and 2.6 to 17.2 microplastics particles/L after treatment. In some samples, the microplastics were not detected or were very minimal in both the influent and effluent.
This picture shows a large microplastic particle that made it through the Ruhleben Berlin wastewater treatment plant. The picture is from the Humboldt University Berlin team in the 2019 iGEM synthetic biology competition.
Wastewater effluent is a widely recognized source of microplastic pollution into freshwater bodies and in agricultural soil, but effective water treatment can reduce these harmful effects. A study in the journal Environmental Science: Water Research and Technology by researchers at the University of Surrey in the UK found that a three-phase wastewater treatment plant could remove 88-94% of microplastics.
Wastewater can cause harmful effects once it re-enters freshwater sources and drinking water sources. Even the waste from wastewater treatment needs to be handled carefully as this would be a source of microplastics. It can disturb agricultural land by introducing a source of fibers into the soil, which could theoretically be toxic or ingested by humans.
5. Arctic Water
The Arctic region lies above the Arctic Circle at 66° 34' north latitude. How much microplastic is in arctic water? Peter S. Ross and his team at the Department of Earth, Ocean and Atmospheric Sciences, University of British Columbia, performed a survey in the Arctic region finding an average of 186 microplastic particles per liter on visual inspection, though this was reduced to a more accurate 40.5 microplastic particles per liter when they used spectroscopic analysis.
Higher microplastic concentrations were detected towards the eastern Arctic which is influenced by the Atlantic Ocean compared to the western Arctic which is influenced by the Pacific Ocean. Seawater samples of arctic water around Svalbard showed close to zero microplastics and icebergs formed in glaciers long before the invention of plastic should have none.
This chart from a study entitled “Microplastics in sea ice and seawater beneath ice floes from the Arctic Ocean” by Kanhai et al. shows concentrations and types of microplastics found in 25 ice cores taken across the North Pole ice cap. Sample 9 was taken almost precisely at the North Pole.
The Global Microplastics Initiative found an almost 8 times higher level of 313 microscopic particles per liter in the Arctic. The different results underscore the difficulty of measuring such broad regions but confirm that the concentrations are worrying no matter which survey is looked at.
It is most likely that ocean currents have carried plastic waste to the Arctic from afar, though comprehensive research on specific microplastic sources in the Arctic is still limited. One known source is discarded plastic fishing nets which regularly wash up on arctic shores from thousands of kilometers away.
Research in 2015 led by Dr. Amy L. Lusher of the Marine and Freshwater Research Centre in Ireland along with the National Institute of Oceanography and Experimental Geophysics (OGS) in Italy suggests that zooplankton, invertebrates, fish, seabirds, and mammals may feed on microplastics. Their surveys found microplastics in 95% of tested surface water samples and in 93% of sub-surface samples. All of which pass through the ecosystem as illustrated by the food web below, and could lead to dangerous toxicological responses or even death.
The International Union for Conservation of Nature (IUCN) points out the human health concerns of arctic microplastics as 40% of US and 50% of European commercial fishing comes from the Arctic region.