Abstract
Microplastic pollution has become a major source of concern, with a large body of literature surrounding the impacts of microplastic ingestion by biota. However, many of these studies utilise virgin microbeads, which are not reflective of environmental microplastics that are rapidly colonised with microbial communities (plastisphere) in marine ecosystems. It is a concern therefore that current evidence of the impacts of microplastics on biota are unrepresentative of the environmental microplastic pollution. In this study, uptake and bioaccumulation of both virgin and Escherichia coli coated microplastics, by European native oysters (Ostrea edulis) were compared, and the physiological responses of oysters to the exposure were investigated. The uptake of E. coli coated microplastics was found to be significantly higher than the uptake of virgin microplastics, with average concentrations of 42.3 ± 23.5 no. g-1 and 11.4 ± 0.6 no. g-1 microbeads found in oysters exposed to coated and virgin microplastics, respectively. This suggests that environmental microplastic uptake into the marine trophic web by benthic filter feeders may be greater than previously thought. The oxygen consumption and respiration rate of oysters exposed to E. coli coated microplastics increased significantly over time, whilst virgin microplastics did not produce any measurable significant physiological responses. However, less than 0.5% of the total amount of administered microbeads were retained by all oysters, suggesting a limited residence time within the organisms. Although microplastics did not bioaccumulate in oyster tissues in the short-term, microorganisms assimilated by the ingestion of coated microplastics may be transferred to higher trophic levels. This poses a risk, not only for wildlife, but also for food safety and human health. The capacity to carry pathogens and expose a wide range of organisms to them means microplastics may have an important role as vectors for disease.
Highlights
Plastic production dramatically increased over the decades, from approximately 2 million Mt. of plastic produced annually in the 1950s, up to 350 million Mt. produced in 2017 (Geyer et al, 2017)
This study indicates that biofilms can make the surface of microplastics more attractive to benthic filter feeders, increasing the number of microbeads ingested
Future studies investigating the effects of environmental microplastic pollution on ecosystem health should consider that the presence of a biofilm can affect the uptake and organismal response to microplastics
Summary
Plastic production dramatically increased over the decades, from approximately 2 million Mt. of plastic produced annually in the 1950s, up to 350 million Mt. produced in 2017 (Geyer et al, 2017). Microplastics can enter the marine environment through many different pathways, including riverine transport, sewage and wastewater effluents, direct release, and atmospheric deposition. A large portion of microplastics suspended in the water column can be captured and directly ingested by planktonic and benthic organisms. Due to their sessile lifestyle, which inhibits avoidance behaviours, oysters and other bivalves are usually more vulnerable to contaminant accumulation, and considered ideal models for ecotoxicology. To date the majority of studies investigating the impacts of microplastics ingestion by aquatic organisms have used virgin or uncolonised plastic particles, which do not reflect conditions in the environment accurately. It is hypothesised that biofilm coated microplastics uptake by filter-feeders will be greater as they may not be recognized as inorganic matter
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