In the 1970s, plastics were first documented in the oceans (Gago et al. 365). Due to the versatile nature of the material, plastic production drastically increased in the second half of the 20th century (Kedzierski et al. 684). Even with strong sustainability efforts worldwide, the international production of plastics surpassed 320 million tons in 2016, with the majority intended for single uses (Silva et al. 2). Each year, there is an approximate 3% increase in worldwide plastic productions (Gasperi et al. 1). In terms of Earth's history, the issue of plastic pollution is in the juvenile stage. The long-term impact of this form of anthropogenic waste is still unknown.
Plastics are durable, versatile and cost-effective polymers (Urban-Malinga et al. 612). Plastics are commercially made and universally used resource (Urban-Malinga et al. 612). The favorable characteristics of plastics, and the improper treatment of plastic waste has made microplastics the most abundant solid waste in every environment (Urban-Malinga et al. 612). Plastic polymers, thermosets, and thermoplastics as well as common additives make up a plastic polymer matrix (Kedzierski et al. 684).
Some of the most commonly produced plastic polymers include polypropylene, polyethylene, polystyrene, polyvinylchloride (PVC), polyamide, polyethylene terephthalate (PET), polyvinyl alcohol (Kedzierski et al. 684). There have been scientific breakthroughs to synthesize biodegradable plastic polymers known as PBAT poly(butylene adipate coterephtalate) (Kedzierski et al. 684). PBAT is designed to have similar physical properties as polyethylene but it takes less time to degrade in the environment. PBAT is the beginning of future innovations leading to reducing the indestructible plastics entering the oceans. PBAT may help to resolve some of the long-term issues associated with future inputs of marine litter.
A microplastic is most commonly defined as a piece of plastic that is under 5mm in size (Gigault et al. 1031). Microplastic is a broad term that contains various subcategories including primary and secondary microplastics, small microplastics, nanoplastics, and microfibers. A primary microplastic is originally manufactured to be within the size range of a microplastic (Cole et al. 2589). The product of a large piece of plastic broking down into microscopic pieces is defined as a secondary microplastic (Cole et al. 2589). Microplastics can be further reduced to small microplastics which are in the range of 0.025mm to 1mm (Gigault et al. 1031). A nanoplastic is a piece of plastic between 1nm and 100 nm in size (Gigault et al. 1031). Microfibers can be inorganic materials, organic materials or synthetic polymers (Gasperi et al. 1).
Microplastics are created by long-term exposure to sunlight, and ultraviolet radiation causes oxidation and photo-degradation of the polymer (Cole et al. 2589). Oxidation of the polymer cleaves the bonds, allowing for greater removal of additives from the polymer (Cole et al. 2589). Photo-oxidation of plastics occur more readily on beaches than in colder, more saline water due to greater exposure to direct sunlight and oxygen (Cole et al. 2589). In addition to mechanical degradation of large plastic pieces, photo-oxidation of plastics lead to the most ubiquitous pollutant in the marine environment (Urban-Malinga et al. 612).
Plain polymers are durable but do not contain the desirable characteristics of the plastics we see in the stores. To be of best use, additives must be added to the polymer matrix to achieve desirable characteristics (Kedzierski et al. 684). Phthalates and adipates are plasticizers which are added to a polymer to make the material more durable and flexible (Kedzerski et al. 684). The effects of phthalates on humans are unknown, but in laboratory settings, organisms displayed issues with the reproductive systems ("Phthalates Factsheet"). Phthalates are present in nearly all industries that use plastic products including the healthcare sector ("Phthalates Factsheet"). Phthalates are commonly added to PVC plastics as well as adhesives, detergents, car parts, clothing, plastic packaging and medical tubing ("Phthalates Factsheet"). The older the phthalate containing product is, the lower the concentration of phthalates ("Public Health Statement for Di-n-butyl Phthalate"). After exposure, the phthalates enter the body and are converted to other chemicals ("Public Health Statement for Di-n-butyl Phthalate"). Approximately 24 hours after exposure, these chemicals have exited the body via the excretory system ("Public Health Statement for Di-n-butyl Phthalate").
Absorption and exposure to adipates can be through inhalation of the vapor and ingestion ("Dioctyl Adipate"). Adipates are known to cause harm to the eyes and central nervous system ("Dioctyl Adipate"). Long term exposure can cause liver damage ("Dioctyl Adipate"). Acute hazards include redness and pain if eyes are exposed, and diarrhea if ingested ("Dioctyl Adipate"). When adipates are introduced into the water system, the plastic additive can be harmful to aquatic organisms ("Dioctyl Adipate").
UV Stabilizers and antioxidants
make the product more durable, and long lasting
Metals
Harms of additives
Gyres are circulating currents caused by pressure gradients, Ekman transport and wind bands ("Ocean Currents"). Oceanic circulation is also driven by worldwide differences in temperature and salinity ("Ocean Currents"). Due to the Coriolis Effect, currents in the northern hemisphere are deflected to the right, and in the southern hemisphere, the left ("Ocean Currents"). Surface currents are driven by friction caused by the wind interacting with the surface water ("Ocean Currents"). Deep ocean currents contribute to thermohaline circulation which involves the temperature and salinity ("Ocean Currents"). The major ocean currents collide with the land creating circular ocean current patterns called gyres ("What Is a Gyre?").
Due to the Coriolis force and the major wind bands, Northern hemisphere gyres circulate counter clockwise, and southern hemisphere gyres circulate clockwise (SOURCE). The gyres function as conveyor belts of water that collect and distribute plastics all around the oceans (Parker). Plastics and microplastics are suspended in the water column and are continually mixed via winds and therefore wave action ("Great Pacific Garbage Patch"). The famous "Pacific Garbage Patch" is located in the South Pacific Gyre ("Great Pacific Garbage Patch"), yet if you sailed over it, you likely would not know (SOURCE).
Microplastics are found in some of the most remote areas on earth that are untouched by anthropogenic activity, leading to the idea of microplastics travelling in oceanic circulation patterns.
Where are plastics found
– The sediments have an average of 10 to 102 particles/250mL, and the surface waters can have up to 105 particles/250mL (Li et al., 2017).
o "The South Pacific Gyre, a circular ocean current that functions like a conveyor belt, collecting plastic trash and depositing it onto tiny Henderson's shore at a rate of about 3,500 pieces a day" (Parker).
" Even marine protected and anthropogenic isolated areas are affected by plastics circulating in the oceans.
o Microplastics are found in 94% of our ocean seawater samples (Miller et al. 245).
Aggregation of microplastics
Why are we worried about this issue? Microplastics have been at the forefront of marine research in recent years due to a combination of increased production of single-use plastics as well as the rapid fragmentation and degradation of macroscopic plastic pieces to microscopic pieces. Since 1977, the number of species affected by plastics (via entanglement or ingestion) has doubled (Urban-Malinga et al. 612).