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Comparative analysis of microplastic release from aquaculture nets under different material, coating, and cleaning technology scenarios
Summary
Laboratory abrasion and field tests showed that nylon aquaculture nets release over five times more microplastics than HDPE or UHMWPE alternatives, with premium coatings paradoxically increasing nylon emissions while having no effect on UHMWPE. Switching to UHMWPE nets and using robotic brushing rather than pressure or cavitation cleaning can substantially reduce microplastic emissions from salmon farming operations.
Aquaculture nets are increasingly recognised as a potential source of microplastic (MP) emissions to the marine environment, yet their contribution has not been quantified. This study assessed MP emissions from aquaculture nets manufactured with different materials and coatings, and subjected to different cleaning technologies, to identify practical reduction measures. Laboratory abrasion tests were conducted on new and used nets made from nylon, high density polyethylene (HDPE), and ultra-high molecular weight polyethylene (UHMWPE), with two coatings (standard and premium). New, uncoated nylon nets released over five times more MP than HDPE and UHMWPE nets, with coatings, particularly the premium formulation, further increasing MP release from nylon nets. UHMWPE nets showed no coating-related increase in MP, suggesting stronger coating integration and higher resistance to abrasion. A custom net pen constructed using different material and coating combinations was deployed at sea. Individual panels were cleaned using pressure washing, cavitation or robotic brushing, and any MP released during cleaning were collected by pumping seawater over stainless steel filters. The resulting MP levels were comparable to background levels, while microscopy revealed that robotic brushing caused less coating damage than pressure or cavitation cleaning. Field sampling during net cleaning at a salmon farm showed sporadic MP emissions, influenced by the presence/absence of lice skirts. At service sites, land-based washing produced detectable MP levels, but filtration systems effectively prevented marine discharge. By integrating laboratory and field data, this study identifies combinations of net materials, coatings and cleaning technologies that could minimise MP emissions and contribute directly to improving aquaculture sustainability and operational practices. • Nylon nets may emit up to 5× more MP than HDPE or UHMWPE alternatives. • Coatings increase MP emissions from nylon nets, but not from UHMWPE nets. • AUV brushing caused less coating damage than pressure or cavitation cleaning in trials. • Field sampling during net cleaning showed sporadic MP emissions.