Abstract
Microplastics (MPs) can readily be ingested by marine organisms. Direct ingestion and trophic transfer are likely to be the main pathway for microplastics to bioaccumulate in upper trophic level organisms. Bioaccumulation potential of MPs in marine mammalian foodwebs is scarcely known. To understand whether microplastics bioaccumulate in marine mammals, a bioaccumulation model for MPs was developed for the filter-feeding humpback whale and fish-eating resident killer whale foodwebs of the Northeastern Pacific. Applying three concentration scenarios for MPs by entering observed water and sediment concentrations as input data (low, high and moderate scenarios), and tested under two different elimination rates (kE) for zooplankton, the model predicted species-specific and foodweb-specific bioaccumulation potential. The predator-prey biomagnification factor (BMFTL, used to assess the ratio of the MP concentration in predator to that in prey adjusted to the difference of trophic levels), involving cetaceans, appeared to be not only lower than one or equal to one (BMFTL ≤ 1 as in resident killer whale/Chinook salmon), but also BMFTL > 1 in some predator-prey relationships (humpback whale/zooplankton). Depending on the magnitude of abiotic concentrations used in the modelling, the trophic magnification factor (TMF) regression analyses over time showed lack of evidence for trophic magnification as the magnification was independent of the trophic level, indicating no changes (TMF = 1; p>0.05), and trophic dilution (TMF 0.05), following 100-365 days. Compared to the high biomagnification behaviour of persistent organic pollutants in marine foodwebs, scarce biomagnification capacity of microplastic was predicted in the cetacean foodwebs. Notwithstanding, the moderate to high microplastic bioaccumulation predicted in some lower trophic level marine organisms highlights the health risks of toxic exposure to marine fauna and coastal communities relying strongly on seafood. This modelling work provides a tool to assess the bioaccumulation potential and impact of microplastics in the marine environment to support risk assessment and inform plastic waste management.
Highlights
Ocean plastics are perversely impacting ecosystems and many marine organisms
The basic principle of the foodweb bioaccumulation model for MPs is based on the notion that the uptake of MPs in primary consumers such as zooplankton is predominantly a filter feeding process that can be described by a bioconcentration factor, BCF: BCF = CB/CW
If CW is known from empirical field data, and BCF is a function of the differential balance from the first order rate constants (i.e., BCF = k1/k2, where k1 is the uptake rate of MP from the water, and k2 is the overall elimination rate of MP through egestion); CB can be calculated for zooplankton by solving equation (1): CB = BCF·CW
Summary
Ocean plastics are perversely impacting ecosystems and many marine organisms. Every ocean is polluted by marine litter, from which about 73% is plastic; and, more than 1,300 species are affected through entanglement and ingestion (Bergmann et al, 2017). The entanglement with and ingestion of ocean macroplastics, including fishing line, plastic bags, and other plastic items, have been reported in about 30–81 species of marine mammals (Moore, 2008; Gall and Thompson, 2015; Kühn et al, 2015). In addition to deleterious entanglements and ingestion, marine debris and plastics serve as vectors for organic pollutants, including polycyclic aromatic hydrocarbons (PAHs), phthalates, nonylphenols, and persistent organic pollutants (POPs) such as polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), and dichloro-diphenyldichloro-ethylene (DDE), which is a byproduct of DDT (Moore, 2008; Gregory, 2009; GESAMP, 2010; Sigler, 2014). One study estimated that a minimum of 5.25 trillion particles weighing 268,940 tons is floating in the world’s ocean (Eriksen et al, 2014)
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