Globally, about 260 million tons of plastic waste was generated in 2016 and projected to 1.8 times by 2030, where 65% are landfilled, dumped, or incinerated and only 12% are recycled. [1] The garbage genre in the Pacific Ocean has covered 60,000 miles (96,560 kilometers), 2.4 times the equator length!
Approximately 12 million tons of plastic waste end up in the ocean each year, and the accumulation is projected to reach 600 million tons by 2040 (see Fig. 1).[2,3] More than 80% of marine plastics are attributable to coastal and inland waste mismanagement. Waste is openly dumped or discarded in an uncontrolled landfill and finally taken to the ocean by wind and waterway.[4,5,6] If you visit a beach, especially a popular scenic area with high population density around, you may find a mess of plastic debris that are littered (e.g., 258,408 items per square meter in Fan Lau Tung Wan, Hong Kong).[7] A single plastic drinking bottle killed 526 hermit crabs, and a stray crab regularly attracts other crabs in search of shells, and they can hardly escape.[8]
Plastics are made to be durable and corrosion-resistant. This durability nature determines that it cannot live in harmony with marine life. Most plastics are not biodegradable and they break down into smaller pieces (e.g., microplastics with size less than 5 mm) and eventually rotate in the ocean eternally and pass up the toxins through the food chain.[9] Some researchers found 693 marine species once encountered marine debris where 92% were associated with plastics. Marine organisms (e.g., sea birds and turtles) are entangled in the plastics mess or mistakenly eat plastics as food.[9,10] More than 17% of those impacted species are near threatened, vulnerable, endangered, or critically-endangered on the IUCN Red List, a well-established inventory of the global conservation status of biological species and used to evaluate the extinction risk of species.[11]
Once aquatic animals (e.g., seals, sea lions, seabirds, turtles) are entangled by plastic fishing nets and ropes, they are tough to escape (see Fig. 2). Worn-out fishing nets are often abandoned by fishermen and lost in the ocean. These nets continually catch and trap more and more organisms, known as “ghost fishing”. A single net can entangle 25 target sockeye salmon, 335 non-target fishes, 68 crabs, and a harbor seal when it was abandoned for only one week off south San Juan Island.[12] However, this is only the tip of the iceberg. In deep water or sediment, despite lack of attention from the media and scientists, the benthic invertebrates (sponges and corals) are also struggling with chronic death due to the entanglement. These benthic communities are animal forests that are a shelter for clownfish and sea stars by adding architectural complexity for several species.[13] Thus, the entanglement may result in a domino effect on a chain of aquatic organisms and impact biodiversity and ecosystem functions (e.g., dampening the impact of storms and hurricanes, dissipating up to 86% of the wave energy).[13] And with an annual accumulation rate of 114,640 pounds fishing nets in the Northwestern Hawaiian Island, the damage is perpetually deteriorating the marine ecosystem.[14]
Unlike the entanglement, plastic ingestion causes no obvious and visible harm to marine animals but likely lead to long-term sublethal damage (see Fig. 3).[15] Most aquatic organisms have ingestion records that show they have mistaken their bits of plastic waste for food—78% of marine birds, 100% of marine turtles, >64 species of marine mammals, and widely impacted fish species.[11] When a sea turtle feeds on a PET water bottle for food, it will still starve to death since it cannot digest the durable plastics and feel full when it is not. Even worse, the plastic intake could hurt the turtle’s stomach by scratching and blocking the intestinal tract. Furthermore, plastics absorb waterborne chemical pollutants that the organisms can be further exposed to after ingestion. Mussels, such as Mytilus galloprovincialis (a Mediterranean mussel), and tidal flat organisms, such as lugworms, were found to accumulate chemicals attached to the contaminated plastic debris in their digestive gland and gills. [16] Ingestion then passes the toxins along the food chain and could eventually impact human health. For example, a piece of plastic debris is eaten by a lanternfish, which is eaten by a squid, which is eaten by tuna; in the end, we eat tuna (see Fig. 4).[17]
To prevent plastic debris from entering the ocean at the source, we at least can start simple to change our daily behavior following the hierarchy: create less waste, reuse what you can, clean PET and HDPE containers before recycling them ... but no to irresponsibly direct throwing to the landfilling trash bin. You can also join a volunteer program of beach cleanups. We people usually cannot feel and recognize the heart of the problem until standing right in front of it.
References
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[2] “The Marine and Polar Theme,” IUCN, Aug. 12, 2015. https://www.iucn.org/theme/marine-and-polar (accessed Oct. 22, 2020).
[3] “Plastic trash flowing into the seas will nearly triple by 2040 without drastic action,” Science, Jul. 23, 2020. https://www.nationalgeographic.com/science/2020/07/plastic-trash-in-seas-will-nearly-triple-by-2040-if-nothing-done/ (accessed Oct. 31, 2020).
[4] J. Boucher, G. Billard, E. Simeone, and J. Sousa, The marine plastic footprint: towards a science-based metric for measuring marine plastic leakage and increasing the materiality and circularity of plastic. IUCN, 2020.
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[9] D. W. Laist, “Impacts of Marine Debris: Entanglement of Marine Life in Marine Debris Including a Comprehensive List of Species with Entanglement and Ingestion Records,” in Marine Debris: Sources, Impacts, and Solutions, J. M. Coe and D. B. Rogers, Eds. New York, NY: Springer, 1997, pp. 99–139.
[10] S. C. Gall and R. C. Thompson, “The impact of debris on marine life,” Marine Pollution Bulletin, vol. 92, no. 1, pp. 170–179, Mar. 2015, doi: 10.1016/j.marpolbul.2014.12.041.
[11] N. Fisheries, “Ghostfishing in Puget Sound | NOAA Fisheries,” NOAA, Nov. 08, 2019. https://www.fisheries.noaa.gov/feature-story/ghostfishing-puget-sound (accessed Oct. 23, 2020).
[12] S. Rossi, L. Bramanti, A. Gori, and C. Orejas, “Animal Forests of the World: An Overview,” in Marine Animal Forests: The Ecology of Benthic Biodiversity Hotspots, S. Rossi, L. Bramanti, A. Gori, and C. Orejas, Eds. Cham: Springer International Publishing, 2017, pp. 1–28.
[13] N. Fisheries, “The Impacts of Ghost Nets on Coral Reefs | NOAA Fisheries,” NOAA, Sep. 25, 2020. https://www.fisheries.noaa.gov/feature-story/impacts-ghost-nets-coral-reefs (accessed Oct. 23, 2020).
[14] P. G. Ryan, “Ingestion of Plastics by Marine Organisms,” in Hazardous Chemicals Associated with Plastics in the Marine Environment, vol. 78, H. Takada and H. K. Karapanagioti, Eds. Cham: Springer International Publishing, 2016, pp. 235–266.
[15]F. Gallo et al., “Marine litter plastics and microplastics and their toxic chemicals components: the need for urgent preventive measures,” Environmental Sciences Europe, vol. 30, no. 1, p. 13, Apr. 2018, doi: 10.1186/s12302-018-0139-z.