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Application of the Blue Mussel (Mytilus edulis) as an indicator of microplastic pollution within the Salish Sea
Summary
This study used blue mussels placed at 11 sites in British Columbia waters to measure microplastic pollution, finding an average of about 2 microplastic particles per mussel, with 91% being fibers. The results suggest mussels could serve as useful indicators of microplastic contamination in marine environments. Since mussels are also a food source for humans, these findings are relevant to understanding our dietary exposure to microplastics.
Plastic polymers less than 5 mm in diameter, called microplastics (MPs), are an emerging contaminant of concern impacting marine organisms globally. The blue mussel (Mytilus edulis) is a prominent bioindicator used to quantify the accumulation of lipophilic contaminants to assess the health of marine environments. For this reason, blue mussels were utilized to establish baseline MP abundances in British Columbia (BC) and assess the practicality of using mussels as indicators of MP pollution. Mussels (n = ~15, 000) were placed in cages at 11 locations within the Strait of Georgia and southern BC waters in the winter of 2017. Mussels were sampled on Day 0, Day 30 and Day 60 post deployment and MP abundances quantified. For all sites combined, a total of 336 suspected microplastics (SMPs) were identified in 171 mussels, resulting in an average of 1.96 (0.13 SE) SMPs per mussel. After correcting for contamination and standardizing for weight, mean SMP abundances averaged 0.43 (0.06 SE) CSMP/GWW (gram wet weight). 91% of the SMPs enumerated were microfibers. A two-factor complete randomized design analysis of variance revealed that mean CSMP/GWW differed significantly over the 60-day period between the 11 sites (p = 0.0003), however, only mussels at the T60 – Powell River site had significantly more CSMPs/GWW. Furthering this, Fourier Transform Infrared Spectroscopy identified a total of 11 of 66 SMP particles (17%) as plastic. A complimentary exposure experiment was conducted in the spring of 2018 to assess particle fate post mussel filtration. Using a combination of polymer types and sizes, mussels were exposed to three environmentally relevant concentrations of MPs. Pseudofaeces, faeces and whole mussels were examined for MPs 24-hours post exposure. While whole mussels had significantly more MPs than pseudofaeces and faeces (p<0.01; mean proportions ranged from 46-68%, 2-4%, 3-8%, respectively) our results confirmed that MPs were both rejected prior to, and eliminated post digestion, suggesting that blue mussels might be a poor indicator of MP pollution. If plastic loads continue to increase as theorized, however, it is probable that the ability of blue mussels to reject and eliminate MPs efficiently will be impacted.