Mesh selectivity of neuston nets for microplastics

Highlights: • Net of 0.333 mm mesh collected more microplastics ≤2.00 mm than 1.00 mm mesh net. • Size selectivity was examined, based on selection curve of 1.00 mm mesh opening. • Size selectivity of net for microplastics was the physical sieving effect of mesh. • Neuston net with 0.333 mm mesh opening rarely retained microplastics ≤0.3 mm. • 60% of microplastics (0.4–1.0 mm) was unaccounted for in 0.333 mm net sampling. Two neuston nets, mesh opening 1.00 mm and 0.333 mm, were towed in parallel. The 0.333 mm net collected more microplastics of longest length ≤2.00 mm than the 1.00 mm net. Mesh selection curve of the 1.00 mm mesh net for microplastics was estimated with the SELECT analysis by comparison of size distributions of microplastics collected by the two nets. Selection curve of the 0.333 mm mesh net, often used as a standard mesh size for microplastic net sampling, was also estimated on the assumption of geometrical similarity between microplastic size and mesh opening for a given retention probability. Approximately 60% amount of microplastics (0.4–1.0 mm) in net sampling with the 0.333 mm net passed through the mesh and was thus unaccounted for. The 0.333 mm net can retain at most 1.5% of microplastics ≤0.4 mm entering the net, and rarely retained microplastics ≤0.3 mm.