Microplastic pollution in urban streams across New Zealand: concentrations, composition and implications

Microplastic pollution in aquatic systems has been reported globally at an alarming rate, with an increasing number of documented negative biological consequences. Research on microplastic pollution in freshwaters has barely begun in New Zealand, and few studies from smaller lotic systems such as streams exist globally. We investigated the extent of microplastic pollution within urban streams across New Zealand and determined if microplastic concentrations were related to human population density and urbanisation of streams. Fifty-two streams were surveyed across five urban agglomerations in January 2019. Microplastics were found in samples from all sites at densities ranging from <1 to 44 items/m³. This concentration range was comparable to global data but lower than reported in another recent New Zealand study, probably due to differences in sampling methodology. Microplastic pollution was similar across all urban centres, and neither length of urbanised catchment nor urban proportion of the stream were significant predictors of microplastic concentrations. These findings suggest microplastic pollution in New Zealand streams are comparable to larger aquatic systems globally, and that smaller urban streams are significant transport pathways for microplastics. We also recommend standardising microplastic sampling methods to a greater extent in the future, to improve comparability across studies.