Microbeads in personal care products are an example of primary microplastics. Primary microplastics were originally produced to be < 5 mm in size, while secondary microplastics result from the breakdown of larger items. Microplastics are often categorized into primary and secondary types. Insights from this review were used to identify recommendations for future research and mitigation. The resultant articles were organized and synthesized into an overview describing the current state of the science. Websites of organizations with interest in this topic were also explored: Food and Agriculture Organization (FAO) and The Group of Experts on Scientific Aspects of Marine Environmental Protection (GESAMP) of the United Nations, European Food Safety Authority (EFSA), United States Department of Agriculture (USDA), Food and Drug Administration (FDA), and National Oceanic and Atmospheric Administration (NOAA). These sites were searched until saturation occurred. We employed the following keywords: microplastics, microdebris, primary microplastics, secondary microplastics, nanoplastics, pellets, marine debris and plastics, microbeads, marine biota, food web, harmful effects, environmental policies, and industry. We conducted an unstructured literature review using PubMed, Google Scholar, Nature’s database, and Science Direct, focused on literature published after 2004 (the year the term, “microplastic,” was introduced). We then explore the life cycle of microplastics including their toxicity and epidemiology in humans and animals, strategies for mitigation and adaptation, and research needs. Where relevant, we provide information about nanoplastics. This review begins with a background on microplastics, ocean dispersal, physical and chemical properties, and degradation. Research to understand and reduce human health risks is critical in order to simultaneously protect consumers and support their nutritional health. Nutritional authorities advise Americans to double their seafood consumption however, awareness or concerns about microplastics in seafood could lead consumers to reduce their consumption. Evidence is evolving regarding relationships between micro- and nanoplastic exposure, toxicology, and human health. In vivo studies have demonstrated that nanoplastics can translocate to all organs. Over time, plastic particles contaminate the marine ecosystem and the food chain, including foodstuffs intended for human consumption. The extent of plastic degradation depends on factors including polymer type, age, and environmental conditions like weathering, temperature, irradiation, and pH. This definition commonly includes plastic pieces in the nano-scale, < 1 μm in size. Additionally, when plastics are exposed to natural forces like sunlight and wave action, plastics will degrade into microplastics-defined as plastic particles under 5 mm in size. For example, more buoyant plastics are more likely to be carried by ocean currents and wind across the environment.
These characteristics also govern where in the water column plastics may be found. When plastics enter the ocean, the rate of degradation and persistence of plastics varies by polymer, shape, density, and the purpose of the plastic itself.
Today, uncollected waste accounts for 75% of these land-based discharges, while the remaining 25% comes from within the waste management system. Waste generation and waste leakage are inextricably linked and proportionally associated with economic development, local infrastructure, and legislation. Discarded plastic materials enter the marine environment as trash, industrial discharge, or litter through inland waterways, wastewater outflows, and transport by winds or tides. While some plastics enter oceans from maritime operations, 80% is suspected to originate from land-based sources.
Approximately eight million metric tons of plastics enter the oceans annually, and conservative estimates suggest 5.25 trillion plastic particles currently circulate in ocean surface waters. Since the 1960s, plastic production has increased by approximately 8.7% annually, evolving into a $600 billion global industry.