Man-made polymers of natural compounds out weight microplastics in Australian seafood: Are we fixating on the wrong thing?

Pollution from synthetic microparticles such as microplastic (MPs) is of global concern. Semi-synthetic microparticles, also known as manufactured natural polymers (MNPs), have received much less scientific attention, despite their morphological similarity to MPs, comparable chemical additives, and the shared potential to act as vector for chemical substances and microorganisms. This study assessed MP and MNP levels in five popular seafood species: sand whiting (Sillago cillata), squids (Loligo spp.), eastern king prawns (Melicertus plebejus), blue swimmer crabs (Portunus armatus), and flatheads (family Platycephalidae) sold fresh in local fish markets from the Gold Coast, Australia. Samples from three tissue types (gill, gut, and muscle) were digested with 10 % KOH and filtered through 5-micron stainless steel filter meshes. Visual microscopic screening was carried out for isolated microparticles, and size, shape, and colour were recorded; then, isolated suspected microparticles were analysed by μ-FTIR to identify the polymer type. Our results show that 88.6 % of seafood available in local fish markets on the Gold Coast was contaminated with at least one particle of MP or MNP. Pelagic species contained a higher particle concentration (0.630 ± 0.064 particles/g) compared to demersal species (0.130 ± 0.019 particles/g. Non-edible tissues exposed to the external environment (gill and gut) contained significantly higher concentrations (0.545 ± 0.046 particles/g) of microparticles compared to edible tissue (muscle) (0.203 ± 0.025 particles/g). There was 1.1-3.2 time more MNPs than MPs in all tissue samples except in prawn muscle and flathead gill tissues, indicating that MNPs may pose a greater threat than previously recognised.