Potential Impacts on Marine Biodiversity

Chronic exposure simply to the physical presence of microplastics has been linked to effects on populations, including the negative influence of micro- and nanoplastics on survival and mortality of different species of zooplankton, which represent a critical energy source in the marine environment [68], or the reduced growth of offspring and reduced survival and fecundity compared with control organisms in crustaceans [10]. The Joint Research Centre of the EC [9] concluded that there is experimental evidence of negative physical/mechanical impacts from ingestion of plastic on the condition, reproductive capacity and survival of individual marine organisms. However, the evidence is restricted to laboratory experiments with organisms from lower trophic levels. These findings imply evidence of harm in natural populations, but quantifying the extent of this harm would be extremely challenging and the extent of harm caused by ingestion is likely to be underestimated, because necropsies have to be carried out. With regard to the chemical transfer of chemicals from plastics, there is still need of more studies for reliable estimates to be made as to the contribution to EDC exposure of marine species arising from microplastic or nanoplastics uptake, and this is a serious knowledge gap. There is already some scientific evidence suggestive of endocrine disruptor activity relating to the intake of chemicals associated with microplastics via the filter-feeding mechanisms of animals like mussels or baleen whales [18], or via the magnifying effect of the food chain in top predators such as the swordfish [69]. Although, in these studies mentioned, it could be questioned what the main source of phthalates is— water pollution, microplastics and/or food chain—the most plausible thesis is that water is not the main source of the pollution: phthalates in water are found in high concentrations only in coastal environments. In the case of the baleen whales, phthalate concentrations were very high in the microplastic and krill to which the animals were exposed, while not being detected in the water, though the relative contributions of krill and microplastics to overall phthalate exposure have yet to be determined.

While it is true that the transfer of persistent organic pollutants such as PCBs to aquatic organisms from microplastic in the diet is likely a small contribution compared to other natural pathways of exposure [70], this would not be the case for nonpersistent pollutants such as some EDCs, which are found in greater concentrations in microplastics than in surrounding seawater or sediments.

Widely used plasticizers with endocrine disrupting properties, for example, dibutyl phthalate, dimethyl phthalate, butyl benzyl phthalate or plastic monomers such as bisphenol A (BPA), can affect both development and reproduction in marine species: effect concentrations of plasticizers in laboratory experiments in some sensitive species such as mollusks, crustaceans and amphibians (including disturbance in spermatogenesis in fish) coincide with measured environmental concentrations in the low nanogram/liter to microgram/liter range. It should be remarked that there are still basic knowledge gaps, including the longterm exposures to environmentally relevant concentrations and their ecotoxicity when part of complex mixtures [61]. Other EDCs, such as alkylphenols, have the capacity to derail male reproductive development leading to feminization or demasculinization of the male form in fish and altered sex in mollusks. Others, such as tin-containing plastic stabilizers, elicit immunological disorders in fishes and induce imposex in gastropods [71].

 
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