Читать книгу Plastic and Microplastic in the Environment - Группа авторов - Страница 49

Free‐floating zooplankton are key members of the marine food web, as they are the connecting link in transferring energy from producer to consumer level in the food chain, and then to the higher trophic levels. They feed upon phytoplankton and the MPs present over the surface of the phytoplankton are accumulated into their bodies (Cózar et al. 2014). Zooplankton consist of many species and have different life cycle stages with a wide range of feeding mechanisms (Wirtz 2012). Studies from lab experiments revealed that these zooplankton are capable of absorbing tiny plastic latex beads (Cole et al. 2013) as MPs of <5 mm have been found in 15 different taxa of zooplankton, from copepods to jellyfish. Ciliated heterotrophic planktons engulf MPs by phagocytosis (Laist 1987). The zooplankton ingests MPs particles, which may either pass through their digestive tract or get stuck in the gut, causing disturbed digestive health, such as lack of hunger due to feeling of filled stomach by MPs, and behavioral changes, which ultimately leads to their death. Sometimes these MPs are successfully excreted from the zooplankton body in the form of pellets (and become part of marine snow), and are distributed to the water column and ultimately settle to the bottom. These MP‐contaminated pellets are then available for benthic organisms. The benthic invertebrates comprise 98% of overall marine biota, which includes oysters, blue mussels, barnacles, lobsters, etc., and these have all been reported to have MPs in them (Nerland Bråte et al. 2014).

According to Possatto et al. (2011) and Lusher et al. (2013), 30% of the fish species that humans extensively consume, including sea bass, are contaminated with MPs. The main exposure route of the MPs in fishes is ingestion during feeding upon MP‐contaminated phytoplankton and zooplankton, or direct ingestion due to confusion with prey. Gills are another exposure root to MPs for marine creatures. This organ serves the purpose of osmoregulation, acid–base regulation, gaseous exchange, and nitrogenous exchange. Interaction of MPs to the gills may cause partial or total blockage, which disrupts these functions and causes fatal harm to the organism (Watts et al. 2016). These MPs often accumulate in their bodies, causing starvation, hormonal imbalance, behavioral changes, and malnourishment, ultimately leading to fatality (Welden & Cowie 2016). Sometimes MPs stuck in the gills of organisms, cause suffocation, and even death of organism. Microplastics of larger size (5 mm) are more harmful as they remain for a longer time in the fish body compared with smaller size (2 mm). Smaller sized MPs are easily excreted with feces. Many of the organisms extensively consumed by humans are reported with MP contamination during field studies, some of them are mentioned in Table 3.1.

Sea birds feed upon fishes. Sometimes they take contaminated fishes with MPs accumulated in them. Sea birds like Albatross and Shearwater feed on the ocean surface and in that way, they take in a huge amount of floating MPs inside their gastrointestinal tract. Ryan (2008) found the presence of MPs in south Atlantic birds. These MPs have many negative impacts on their bodies, including starvation due to lack of hunger caused by MPs accumulated in their gastro‐intestinal tract, and blockage of respiratory organs like gills leading to suffocation and ultimately death. The sediment water interface is the main hub of these artificial polymers due to sinking and sedimentation. MPs have lower density than the oceanic water; however due to biofouling (deposition and colonization of microorganisms on any surface exposed to them in water) by microorganism they settle down. Biofouling increases the density of MP and make it more dense than the oceanic water, although this may take up to a week, a month, or more than year (Fazey & Ryan 2016). These phenomena are highly surface area‐to‐volume ratio dependent, as smaller fragments have more surface area‐to‐volume ratio than the larger debris (Kowalski et al. 2016). Therefore, smaller sized particles lose their bounce earlier and settle in benthic environments. The fecal matter of zooplanktons also contain MP pellets; they ingest the MPs and are unable to digest to any further, simpler form of nutrition, so what is ingested is excreted. These also settle to the bottom. MPs in fecal materials speed up its sinking rate in the water column (Cole et al. 2016). These are then bioavailable to the benthos and become the part of benthic food system.

Table 3.1 The occurrence of MPs in marine organisms reported in some studies.

Marine organisms contaminated with MPs	Sampling location	Occurrence of MPs	Specific detail	References
Caretta caretta (54 sea turtle samples)	Adriatic Sea	35%	Fatality seen in juvenile turtle due to debris ingestion	Lazar & Gračan (2011)
Lampris sp. (595 samples)	North Pacific	19%	Highest debris ingestion seen in mesopelagic (rarely comes in contact with surface water)	Choy & Drazen (2013)
Mesoplodon mirus	North and west coasts of Ireland	85%	MPs detected throughout the digestive tracts	Lusher et al. (2015)
26 different fish species (178 individuals sampled)	Saudi Arabian Red Sea coast	15%	Highest contamination was found in Parascolopsis eriomma species which feed on benthic organisms	Baalkhuyur et al. (2018)
Oysters	China coast	84%	Average conc. of MPs: 0.62 items/g (wet weight) or 2.93 items/individual	Teng et al. (2019)
150 analyzed fish (50 per species)	Northeast Atlantic Ocean	49%	Lipid oxidative damage found in gills and muscle which cause neurotoxicity	Barboza et al. (2020)
European Sardine	Northwestern Mediterranean Sea	58%	Positive relation between MPs and parasite ingestion	Pennino et al. (2020)
Anchovies (45 samples)	Madura Strait, Indonesia	335 plastic particles: 63% fibers, 34% fragments	2.98% of total MPs found in all anchovy samples	Guntur et al. (2021)

Other sea organisms like turtle, whale, seal, etc., are also at a high risk of MP accumulation and toxicity (Egbeocha et al. 2018). Whales have high lipid content in their body; therefore, they are more prone to accumulate MPs in their blabber, stomach, and intestines. Polar bears in the arctic region are also highly infected with MPs (Singh et al. 2020). Plastic debris reaching oceans from populated landmasses travels long distances along the water current and are distributed to every part of ocean over time, during which fragmentation of plastics also occurs, generating MPs, today their presence is reported in fish bodies in polar areas of the Arctic.

According to Food and Agriculture Organization (FAO, 2002) there are four pillars of food security (introduced in World Food Summit 1996); accessibility, availability, utilization, and stability. Although, due to the presence of MPs in every segment of our ecosystem, two pillars, i.e. food availability and utilization, are compromised in the case of marine food (De‐la‐Torre 2020). Organisms consume these MPs but their enzymatic actions are unable to break down the polymeric particles of the MPs, and this hinders the process of assimilation of other available nutrients. This causes starvation and lack of nutrition and ultimately leaves them undernourished. These organisms which are contaminated with MPs reach to humans in their food sources as those food sources are already nutrient deficient, so they are not sufficient for a human diet. Instead of nutrients, humans may meet with potential health threats due to MPs (Figure 3.2).

Figure 3.2 Plastic web cycle: Plastic starting its journey from human and returning back to them.

Source: chaiyapruek/Adobe Stock.