Microplastics
Background and Sources of Microplastics
Microplastics are an emerging environmental concern with potential human and ecological health effects. Microplastics are generally defined as plastic particles between 1 nanometer (nm) and 5 million nm (or 5 millimeters [mm]) in size. Particles larger than 5 mm are often referred to as macroplastics while particles less than 1 nm are considered nanoplastics, a subgroup of microplastics.
Primary microplastics are intitionally manufactured at small sizes. Examples include cosmetic beads, glitter, seed coatings, and pellets or nurdles (small, round, lens or disc shaped plastic pieces between 2 and 5 mm). Raw plastic materials are often transported as pellets or nurdles before being melted and molded into other products. Various pathways in the environment lead to the fate of macro- and microplastics breaking down to form secondary microplastics. Secondary microplastics make up the majority of microplastics found in the natural environment.
Some common sources of secondary microplastics are:
- Degradation of plastic items, such as food containers, toys, packaging, cigarette filters, and other items
- Fibers shed from synthetic textiles and clothing
- Particles from the breakdown of tires on road surfaces
Size is the only common parameter for microplastics since chemical composition and shape can differ extensively. The type of material the plastic is made from and method used to make the different types of plastic polymers results in a variety of additives, colorants, and other toxicants in a single piece of plastic. Plastic particles can take on countless shapes given their versatility of use: fibers, films, foams, beads or spheres, pellets, and fragments. The shape of secondary microplastics is influenced by the material it is made from, type of weathering, and time spent in the natural environment.
Commercial production of plastics began almost a century ago and has been increasing ever since. Demand for a variety and number of plastic products increased during this time, and so did plastic waste. Plastic waste is estimated to have increased from 390,000 U.S. tons in 1960 to over 35 million U.S. tons in 2018. As a result, microplastics have been found across the globe in wildlife such as birds and fish, and in all environmental media.
Routes of Exposure
The wide use of plastics has increased human exposure to microplastics through ingestion, inhalation, and contact with skin. Microplastics may be consumed through the ingestion of particles in drinking water, food, or from accidental ingestion of soil. When plastic food packaging breaks down due to heat or other environmental conditions, microplastic particles may leach, or seep, into the food and be ingested. Both aquatic and land animals may ingest microplastics, which can transfer up the food chain to humans. The small size of microplastics allows plastic fragments to become airborne, which leads to an increased risk of exposure through inhalation. Contact with skin may also be a route of exposure to microplastics, as some nanoplastics are small enough to be absorbed by the skin. Click here to learn more about the distribution, fate, and transport in various environmental media.
Microplastics Sources, Pathways and Fate Conceptual Diagram.
Image credit: Jeffrey L. Corbett, USGS
Ecological Effects
Microplastics and nanoplastics are prevalent throughout the entire ecosystem including soil, water, sediment, air, plants, and animals. Studies show that these plastic particles can be accidentally consumed by an individual or travel through the food web from primary producers at the bottom of the food chain to consumers at the top, resulting in negatives impacts to aquatic and terrestrial wildlife.
The toxicity of a plastic particle is largely dependent on its size, shape, composition, and ability to bind with other chemicals present in the ecosystem. The larger, more rigid particles can lodge in the gut of consumers resulting in intestinal blockage whereas smaller (nano) particles and fibers can cause metabolic, behavioral, and developmental impacts following ingestion. Additionally, microbial communities (biofilms) can form on the surface of these particles. These biofilms may contain pathogens and other toxic substances such as polychlorinated biphenyls (PCBs), per- and poly-fluoroalkyl substances (PFAS), and mercury, therefore increasing toxicity and adverse impacts to the ecosystem population.
Micro- and nanoplastic research is rapidly evolving to better define toxicological impacts to aquatic and terrestrial wildlife, as well as to determine reliable field and laboratory methods for measuring particle concentrations across all environmental media.
Human Health Effects
The health effects of microplastics are still being identified. The most consistently reported health effects in current scientific research include:
- decreased immune response,
- increased inflammation and oxidative stress, and;
- organ effects including changes in liver, kidney, and lung tissue.
Research on long term health effects is ongoing.
Health effects from ingestion and inhalation of microplastics can vary greatly based on the physical and chemical composition of the microplastic particles. When ingested, smaller particles may be absorbed into the GI tract, and increased amounts can leave less room for nutrients and food to be absorbed. When inhaled, smaller particles are more likely to enter cells in the lungs and cause inflammation in the respiratory system.
The different shapes, sizes, and makeup of microplastics influence the amount of chemical toxins and microbes, such as bacteria and viruses, that can adhere to their surface. As a result, the hazards associated with microplastics are broad because they are unique to the particle shape, size, and composition.
Regulatory Status
Federal programs such as the Federal Microbead Free Waters Act of 2015, Save Our Seas Act 2.0, and the Clean Water Act all take steps toward reducing plastic waste in waters. The 2022 bipartisan Infrastructure Investment and Jobs Act designated $50 billion toward drinking water and wastewater improvements, including emerging contaminants such as microplastics. In 2023, US EPA released a Draft National Strategy to Prevent Plastic Pollution outlining three primary objectives—reduce plastic pollution during production, increase reuse and composting of materials, and capture and remove plastic pollution from the environment to prevent it from entering waterways. Altogether, these measures provide innovative approaches to preventing and reducing plastic pollution.
