Atmospheric microplastics, their accumulation in vivo and potential toxicity.

Over 8 billion tonnes of plastic have been made since mass production began in the 1950s. Eighty per cent of this has gone to landfill or the natural environment. Consequently, plastic litter is widespread and it persists. Upon exposure to sunlight, plastic slowly degrades into microscopic particles and fibres known as microplastics. Microplastics are also purposefully manufactured, such as microbeads used in personal care products. Microplastics have been found in food and the air we breathe, prompting speculation about risks to public health.

If small enough to be inhaled, airborne microplastics could enter the airway. From here they may be cleared with mucus to the gut, or they may enter the deep lung where they interact with lung fluid and cells. As plastic cannot be broken down, microplastics have the potential to persist in our bodies by embedding in tissues or entering cells. Following exposure, there are several ways in which microplastics are predicted to cause harm. They may trigger an inflammatory response, as they resemble foreign bodies which immune cells try to eliminate. They may also carry a cocktail of chemicals. These include additives that are incorporated during plastic product manufacture, and chemicals concentrated on their surface from the surrounding environment. Such chemicals are known to cause genetic mutations, cancer and reproductive effects. Additionally, microplastics carry a novel community of microbes, including harmful types. Given the risk of human exposure, there is an urgent need to assess the potential health impacts of microplastics. However, a solid evidence base for population exposure - including microplastic concentrations, types and sizes - is lacking.

This fellowship aims to address this by assessing whether microplastics down to an inhalable size are airborne; if humans are exposed to microplastics via the air; and whether exposure could lead to health effects. The research will be conducted at the Medical Research Council (MRC)-Public Health England Centre for Environment and Health (King's College London) in partnership with the MRC Toxicology Unit (Leicester). Instruments which measure air quality will be used to collect airborne particles. Samples will be assessed with a microscope coupled to an instrument capable of detecting unique chemical signatures, known as Raman spectroscopy, to detect microplastics. Microplastics will be counted, sized, and the type of plastic identified. To assess whether humans are exposed to microplastics, human lung tissue samples routinely-collected during medical procedures will be screened. Samples will be viewed under a microscope coupled to a Raman spectrometer and suspicious particles characterized as above. To understand the potential for microplastics to cause harm, varying characteristics of microplastics - such as plastic type, size, shape and surface chemistry - will be screened in a an animal model. The outcomes of the proposed project are to 1) have a standard method to carry out monitoring of microplastics in the air in different environments (such as urban, coastal and rural); 2) to determine the suitability of tissue as an indicator of exposure; and 3) have an overall increased understanding of the risk that microplastics present to human health. Classifying microplastics by plastic type will highlight those plastics which require improved regulation via resource and waste management, and material and product design.

An estimated 8.3 billion tonnes of plastic have been manufactured since mass production began in the 1950s. Eighty per cent of this has accumulated in land fill or the natural environment. Plastic can photodegrade into particles and fibres known as microplastics (<5 mm). Microplastics have been reported in dietary sources and the air, prompting speculation about risks to public health. A solid evidence base characterising population exposure, however, is lacking.

Plastic fibres have been observed in pulmonary tissue. There are several mechanisms through which harm could occur-for example, by triggering inflammation, or releasing associated priority pollutants, including monomers and additives, although no definitive studies on health effects have been conducted. During this fellowship I propose to assess the human health risks of microplastics. I will address three novel issues:

WP 1. The extent and sources of atmospheric microplastic contamination. Monitoring at an urban site will be conducted. Samples will be inspected with Raman microscopy to characterise suspicious particles, including the inhalable size range. A standardised method will be established for application in contrasting environments.

WP 2. Microplastic uptake and accumulation in vivo. Human pulmonary tissue will be analysed using a combination of histopathology and Raman microscopy methods to identify and characterise potential microplastics. This will indicate whether microplastic exposure occurs in vivo, whilst validating a tissue screening method.

WP 3. The potential toxicity of microplastics. The toxicity associated with microplastic size, shape and type will be screened in hazard mechanism studies. Molecular changes in target tissues will be assessed to determine the potential mechanistic toxicity of exposure to and accumulation of microplastics. Identifying hazardous parameters of microplastics will guide waste management, polymer engineering and product design.