Shellfish aquaculture often uses large amounts of plastic equipment and has been suggested as a potential source of microplastic contamination in the marine environment. To determine the influence of shellfish aquaculture on microplastic concentrations in bivalves and their environment, we compared microplastic particle (MP) concentrations in Manila clams Venerupis philippinarum and Pacific oysters Crassostrea gigas grown on commercial shellfish beaches with those in individuals of the same species grown on nearby non-aquaculture beaches in 6 regions of coastal British Columbia, Canada. MP concentrations did not differ between shellfish aquaculture and non-aquaculture sites for either bivalve species, sediment, or water samples. Plastic presence differed by site and oysters on sites with many synthetic anti-predator nets contained significantly, yet marginally, more MPs than those on sites without (0.05 vs. 0.03 g -1 dry-tissue weight on average). However, analysis of suspected MPs using Fourier-transform infrared spectroscopy in dicated a predominance of fibres from textiles (including nylon and polyester), which are not typically used in shellfish aquaculture, suggesting that this may be caused by the larger average body weight of oysters grown at non-aquaculture sites rather than by the degradation of aquaculture infrastructure.

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