Researchers from King’s have carried out the first study of microplastics in the atmosphere in London to determine what people within the city might be exposed to and where this comes from.
In the study published today in Environment International, they found that microplastics are present in the air in London at higher abundances than any other major city examined so far.
Their findings indicate that cities are a likely source of microplastics to the wider environment with the weather and meteorological patterns having little influence on their abundance in this urban environment.
Microplastics are made through the fragmentation or scuffing of larger pieces of plastic, such as from degraded plastic litter or fibres from synthetic clothing.
They are also purposefully manufactured for a range of applications, although the EU has proposed to restrict the use of intentionally added microplastics in products.
There may be other sources of microplastics which have not been discovered yet.
Researchers used a rain gauge with a funnelled surface to collect atmospheric deposition (dust naturally settling out of the atmosphere) in central London during winter 2018. This was filtered and analysed using a specialist instrument which detects unique chemical ‘fingerprints’ of the particles to identify their composition.
They found that:
- Microplastics were present in every sample taken in London and greater than previously reported by any other study.
- Levels of microplastics were higher in London compared to Dongguan, China and Paris, France and Hamburg, Germany.
- Levels of microplastics in London are almost 20 times greater than in the French Pyrenees when comparing particles of the same size.
- 92% were fibrous microplastics that come from the wear down of plastic textiles including clothing, upholstery and carpets.
- The other sources include fragments from larger plastic products, films from thin plastic items such as disposable plastic bags and foam from polystyrene items.
- Microplastics can become airborne and travel as far as 95 km by the wind however local sources have a greater influence on deposition in central London.
Lead author Dr. Stephanie Wright, UKRI Rutherford Fellow in the School of Population Health & Environmental Sciences at King’s said:
“We found some of the highest reported levels of microplastics in atmospheric dust, with local sources appearing influential.
Fibres were the most abundant for the size range we looked at, mirroring the marine environment. From where microplastics are emitted and for how long they are airborne remain unknown but are key for understanding long-range transport potential to the wider environment.
An important next step in predicting risk is to estimate human exposure to airborne microplastics.”
Although the impact of microplastics on humans is still relatively unknown, occupational studies indicate that workers exposed to very high levels of plastic dust suffer chronic inflammation of the airway, in some (worst) cases interstitial lung disease and tissue scarring.
Despite not all sources of microplastics being known and the impact on human health, the authors suggest there can be ways to mitigate your exposure.
The authors are now looking at longer-term patterns of microplastic deposition and will begin to look at spatial distribution, comparing different types of environments such as rural, urban, coastal and industrial, to understand its entry to the wider environment.
They are also quantifying microplastics in size fractions capable of depositing in the human airway, in order to begin to understand exposure via the air and the consequences for human health.
Microplastics are generally characterised as water-insoluble, solid polymer particles that are ≤5 mm in size (Bergmann et al., 2015). A formal definition for the lower size boundary does not exist, but particles below 1 μm are usually referred to as nanoplastics rather than microplastic (Koelmans et al., 2015).
Although microplastics are often detected in the environment, the risks they pose are debated and largely unknown.
One key challenge in assessing the risks of microplastics to humans and the environment relates to the variability of the physical and chemical properties, composition and concentration of the particles. Further, microplastics in the environment are difficult to identify and standardized methods do not exist (Mintenig et al., 2018).
The dominant source of microplastics often is the fragmentation of larger plastics or product wear, however the rate of fragmentation under natural conditions is unknown (Eerkes-Medrano and Thompson, 2018).
These challenges and unknowns hamper the prospective assessment of exposure and risk (Koelmans et al., 2017). In this uncertain field, regulatory efforts to examine microplastic safety have been raised (SAM, 2018a, b).
The presence of microplastics has been reported for air samples, food and drinking water (EFSA, 2016; Gasperi et al., 2018; Lusher et al., 2017; Van Cauwenberghe and Janssen, 2014; Wright and Kelly, 2017; Yang et al., 2015) and recently, the implications of microplastics for human health have been reviewed (Wright and Kelly, 2017).
Although microplastic exposure via ingestion or inhalation could occur, the human health effects are still unknown. If inhaled or ingested, limited data from animal studies suggest that microplastics may accumulate and cause particle toxicity by inducing an immune response (Deng et al., 2017; Gasperi et al., 2018).
Chemical toxicity could occur due to leaching of plastic-associated chemicals (additives as well as adsorbed toxins) (Diepens and Koelmans, 2018; SAPEA, 2019). Such effects are likely to be dose-dependent, however knowledge of exposure levels is currently lacking. Furthermore, biofilms growing on microplastics may be a source of microbial pathogens (GESAMP, 2016).
Hence, although there are potential chemical, particle and microbial hazards associated with microplastics, current exposure levels, including through drinking water need to be assessed first.
The ubiquity of microplastics of all sizes in surface water, groundwater and wastewater (SAPEA, 2019), has raised the question if pollution of drinking water occurs. To date, there is only a limited number of studies that address this issue and they indeed reported the presence of microplastics in tap water and bottled water (Kosuth et al., 2018; Mason et al., 2018; Mintenig et al., 2019a, Mintenig et al., 2019b; Schymanski et al., 2018).
Some of these studies triggered a great deal of attention in the scientific community as well as the media, putting the issue of human exposure to microplastics via drinking water high on the agenda of public health agencies worldwide. More broadly, ensuring safe drinking water is high on the political agenda, with a dedicated target on safe and affordable drinking water under the Sustainable Development Goals (SDG 6) (WHO and UNICEF, 2017).
To date, about 50 studies exist that provide concentration data for microplastics in drinking water or its freshwater sources, i.e., surface water and groundwater, as well as (indirectly) wastewater. These studies provide data for specific types of water, but methods of sampling, isolating, purifying and identifying microplastics vary enormously among studies.
A systematic review of methodologies used and study characteristics is currently lacking. There are several scoping reviews that emphasise the relevance of microplastics in freshwaters (Eerkes-Medrano and Thompson, 2018; Li et al., 2018; Wagner et al., 2014) or that specifically discuss processes or models in freshwaters (Kooi et al., 2018).
We are aware of only a limited number of reviews that touch upon methodologies and concentration data (Eerkes-Medrano and Thompson, 2018; Li et al., 2018).
Besides variation in methodologies used and concentrations reported, existing studies are likely to vary with respect to the level of quality assurance deployed.
The quality of microplastic research has been debated recently (Burton, 2017; Connors et al., 2017; Koelmans et al., 2016) and has been quantitatively assessed for studies on microplastic ingestion by biota (Hermsen et al., 2018).
However, a critical review of studies reporting concentration data in freshwater and drinking water, which also evaluates the quality of applied sampling methods, microplastic extraction and identification steps, is currently lacking.
For chemical risk assessments in a regulatory context, quality criteria have been set in order to be able to evaluate the reliability of data from toxicological studies (Kase et al., 2016; Klimisch et al., 1997; Schneider et al., 2009).
Such criteria contribute to the harmonization of the hazard and risk assessments of chemicals across different regulatory frameworks. Recently, Hermsen et al. proposed a weight-of-evidence scoring method for studies of microplastic ingestion by marine biota (Hermsen et al., 2018).
This method defined minimum quality criteria for various aspects of the analytical procedure, such as sampling, sample treatment, use of controls and polymer identification. It assigns a score for each aspect and provides a total reliability score for data reported in a study.
Such a method can also be developed for the analysis of microplastics in freshwater samples, and can be applied to quantify the relative reliability of reported concentration data.
The aim of the present paper is to critically review the available literature on microplastics in drinking water and its freshwater sources, from a quality assurance perspective and by using a quantitative approach. Wastewater studies were also assessed as these are discharged into the environment.
Further aims are to review data on concentration, polymer type, shape and size distribution data across studies. Guidance is provided to improve the quality of future occurrence studies.
Our paper is organised as follows. We first present the key areas that should be assessed to determine the reliability of studies. These areas are presented in separate sections and are: sampling method, sample size, sample processing and storage, laboratory preparation and clean air conditions, negative controls, positive controls, sample treatment and polymer identification.
For each of these areas we discuss quality assurance aspects, considerations for scoring, and present the assessment scores for each of these criteria. Subsequently, the combined overall reliability scores are discussed, followed by a discussion on implications for human health risk assessments.
In the section thereafter we discuss the outcomes of the reviewed studies. An overview of the concentrations, shapes and polymer types measured is provided and trends are discussed with respect to sample type, location or system characteristics. Finally, we provide recommendations to improve the analysis of microplastics in water samples and summarize the key conclusions.
More information: S.L. Wright et al. Atmospheric microplastic deposition in an urban environment and an evaluation of transport, Environment International (2019). DOI: 10.1016/j.envint.2019.105411
