Microplastics are small plastic fragments less than 5 millimeters in length. These tiny particles are pervasive across various global environments, found in oceans, freshwater systems, soil, and even the atmosphere. Their widespread presence means these plastic pieces have also been detected within the human body.
Environmental Sources of Microplastics
Microplastics enter the environment through two main classifications: primary and secondary. Primary microplastics are intentionally manufactured at their small size for specific uses, such as microbeads once found in some personal care products or the plastic pellets, known as nurdles, used in industrial manufacturing. Synthetic fibers, like those from nylon textiles, also fall into this category, shedding during washing processes and directly entering wastewater systems.
Secondary microplastics, which constitute the majority of microplastics in nature, result from the breakdown of larger plastic items. Everyday objects such as plastic bottles, bags, and packaging degrade over time due to exposure to sunlight, wind, and waves. Particles from tire wear, shed during normal vehicle use, also contribute significantly to secondary microplastic pollution in outdoor environments.
Ingestion Through Food and Water
Ingestion is a primary pathway for microplastic entry into the human body, occurring through contaminated food and water sources. Seafood is a notable route, as fish, shrimp, and bivalves like mussels ingest microplastics directly from polluted waters. Studies have reported microplastic particles in fish and mussels. Bivalves, often consumed whole, including their digestive tracts, represent a direct exposure scenario.
Beyond seafood, microplastics have been identified in various other food products. Table salt, for example, frequently contains microplastics. Honey and beer have also shown contamination with microplastic fibers and fragments. These contaminants can originate from environmental exposure during production, processing materials, or even packaging.
Drinking water also contributes to microplastic ingestion. Bottled water contains higher concentrations of microplastics compared to tap water. The source of these particles in bottled water can include the plastic bottle itself or its cap. While tap water undergoes filtration, complete elimination is not achieved, leading to their continued presence in municipal supplies.
Inhalation of Airborne Particles
Inhalation is another primary route for microplastic entry into the human body, as these tiny particles become airborne both indoors and outdoors. Indoor environments often exhibit higher concentrations of airborne microplastics compared to outdoor settings. Fibers from synthetic textiles like carpets, furniture, and clothing are major indoor sources. Factors such as human activity, ventilation rates, and the presence of textiles can influence indoor microplastic levels.
Outdoors, sources include urban dust, which contains particles from tire wear and degrading plastic litter on streets. Industrial zones and high-density urban areas also show higher outdoor microplastic abundance. These microscopic particles, particularly those smaller than 10 micrometers, can be breathed deeply into the respiratory system. Once inhaled, microplastic fibers have been detected within human lung tissue.
Dermal and Other Exposure Routes
Dermal contact represents a less understood but potential pathway for microplastic exposure. Microplastics can be present in cosmetics and personal care products, which are applied directly to the skin. While particles larger than 100 nanometers do not penetrate intact skin, nanoplastics may bypass the stratum corneum, the outermost layer of the skin.
Despite being considered a minor route compared to ingestion and inhalation, research suggests that dermal uptake of microplastics and nanoplastics may induce skin alterations and inflammation. Studies have shown that higher concentrations of particles applied to the skin can lead to deeper penetration into the epidermis and dermis. This area remains an active field of scientific inquiry to understand its contribution to overall human exposure.