Seafood with a Side of Microplastics
By Iva Fedorka
Plastic waste has been found in the Arctic Circle, at the top of Mount Everest, and at the bottom of the oceans. These tiny plastic particles or microplastics are frequently ingested by marine animals in our food chain, and we do not yet fully understand how these microplastics may affect aquatic and human health.
Plastic, Plastic Everywhere
Plastic production has increased annually by 8.7 percent since the 1960s and is now a global industry worth hundreds of billions of dollars. From four to 12 million metric tons of plastics find their way into the oceans every year and the amount of plastic in oceans is expected to outweigh the fish population by 2050. Conservatively, 5.25 trillion plastic particles were circulating in the Earth’s surface waters in 2018.
Eighty percent of these plastic waste materials are trash and items discarded from industrial discharge, inland waterways, and wastewater outflows. Approximately three-quarters of this trash is uncollected waste and the waste management system contributes the remaining 25 percent.
What Are Microplastics?
The term microplastics (MP) was introduced in 2004 to describe plastic particles from 0.1µm to 5mm in size. They vary in size, shape, chemical composition, and polymer type. The most common resins are polyethylene and polypropylene. Some MP were manufactured in a small size (“primary” MP), while others (“secondary” MP) are created as larger items degrade.
Sources of Microplastics
Personal care products (like exfoliants) contain microbeads, one type of primary MP. The daily release of microbeads into marine habitats is estimated to be eight billion in the United States alone. Industrial abrasives and pellets used to make larger plastic items are another significant source of primary MP. Secondary MP may include textile microfibers and dust from tires, along with the particles created by the degradation of other plastic items.
Even if plastic manufacturing were stopped completely, secondary MP would continue to be produced from existing plastic waste as that litter degrades. The rate of degradation depends on the resin or polymer, and the type, shape, density, and age of the plastic item. Environmental conditions (weather, temperature, radiation, and pH) also affect the rate of degradation.
Although plastics are durable, they can still be affected by biodegradation (decomposition by microorganisms), photo degradation by sunlight or photons, thermo or thermal oxidation (slow molecular deterioration at moderate or high temperatures), and the hydrolytic effects of water.
Although many reports have been published about MP pollution in seafood and aquatic environments, a lack of standardized sampling, identification, quantitation, and analytical methods has produced inconsistent results.
Sample Collection and Prep
Water, sediment, and the gastrointestinal tracts of aquatic animals are the usual samples of choice. Surface water is collected using nets or trawls. Sediment can be gathered by shovel or core sampling. The livers, gills, guts, and other organs of aquatic organisms are dissected. The MP is then separated from the matrices using density determination, chemical digestion, and other sample preparation methods.
Characterization and Quantification
Once the MP are segregated, they are chemically evaluated to identify the specific types of polymers they contain. Currently, scientists characterize MP using gas chromatography/mass spectrometry (GC/MS), Fourier transform infrared spectroscopy, Raman spectroscopy, pyrolysis, and other imaging techniques.
The MP content of water, sediment, and biota are typically expressed as “particles per m3,” “particles per m2,” or “particles per individual”, respectively. However, many assessments may not include nano-sized plastic particles (with a size range from 0.001 to 0.1µm), for which effective measurement methods are not always available.
In addition to the resins, chemicals are added in the plastic-making process. As much as 4 percent of MP weight may be plasticizers, pigments, antimicrobial agents, stabilizers, and other additives. These chemicals can leach into the surroundings from the plastics. Leaching increases with degradation as the surface-to-volume ratio of MP increases.
MP has also been shown to absorb persistent organic pollutants (POPs), including polychlorinated biphenyls (PCBs), polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides, flame retardants, and other by-products of consumer goods or municipal waste.
Although we are advised by nutritional authorities to eat more seafood, concerns about MP content may actually lead to reduced consumption. More research about human and animal health risks from MP is critical if we are to protect consumers and the environment.
Although many water creatures that ingest MP have been studied, more research is needed. Since some MP are denser than water, they sink and bottom-feeding organisms are more likely to ingest them. Other MP are less dense and may be eaten by fish and other species that inhabit the water column.
Preventing and removing MP from water is also a major issue. Engineering and biotechnological tools, such as advanced water treatments, could help to control, reduce, or even eliminate MP pollution. Because the elimination of plastic waste is also affected by economic development, local infrastructure, and legislation, making changes to established habits, practices, and employment will be a challenge.