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Impact of a recent invader on a freshwater top predator exposure to microplastics and flame retardants
Summary
Scientists studying rivers in Portugal found that an invasive crayfish species may be helping spread microplastics and toxic flame retardant chemicals up the food chain to otters, top predators that eat the crayfish. This matters beyond otters because it shows how invasive species can act as a hidden "delivery system" for pollutants that build up in animals we eat, like fish and shellfish — a reminder that plastic and chemical pollution in waterways doesn't stay contained, and invasive species could make human exposure through seafood worse than expected.
Biological invasions and pollution are pervasive pressures on freshwater ecosystems, yet their combined effects on top predators remain poorly understood. We tested whether the non-native signal crayfish, Pacifastacus leniusculus (Dana, 1852), increases exposure to microplastics and polybrominated diphenyl ethers (PBDEs) in Eurasian otters, Lutra lutra (Linnaeus, 1758). Along the Rabaçal and Tuela River basins (NE Portugal), 10 invaded and 4 non-invaded sites were surveyed. We quantified riverbank macroplastics (ATR-FTIR), microplastics (Raman microscopy), and PBDE congeners (GC–MS) in otter spraints and crayfish. Macroplastics were dominated by polyethylene and polypropylene, with no spatial differences in abundance or colour. Microplastics were detected in otter spraints and signal crayfish; blue fibres (47%) and nylon (56%) were prevalent, and otter spraints from invaded sites contained higher microplastic loads. Blue fibres covaried between crayfish and otters, suggesting trophic transfer. PBDE concentrations generally did not differ between sites, but otter spraints from invaded sites showed higher 5-MeO-BDE-100 and BDE-183 levels (P = 0.047, P = 0.040, respectively). BDE-47 was higher in Tuela than in Rabaçal. No sex-related differences were found in crayfish. These results indicate a coupled particulate–chemical pathway by which non-native crayfish may intensify otter exposure to microplastics and PBDEs, highlighting the need to include biological invasions in contaminant risk assessments.