Abundances and characteristics of small (< 0.3 mm) and large (0.3–5 mm) microplastics found in Aotearoa New Zealand beach sediments

Microplastic contamination has been widely documented across the globe, however few reports have been published on this topic in Aotearoa New Zealand. In this study, microplastic contamination was assessed in beach sediments from 23 sites across three regions of the country: Northland, Waikato and Canterbury. A protocol was devised and validated to separately isolate, quantify and characterise microplastics in two size ranges: large (300-5000 μm) and small (< 300 μm) particles. The size distributions at all sites were strongly skewed towards small microplastics, which represented >99 % of the total particle count. Overall mean abundances were 3.3 particles kg-1 (range 0-27) and 788 particles kg-1 (range 0-9818) for large and small microplastics, respectively. No significant differences in concentrations of either size category were observed between the three regions or when comparing west coast with east coast sites. The particles were also characterised with respect to morphology, colour and chemical composition. Fibres (42 %) and fragments (39 %) were the most common morphologies. The most abundant polymer types were polyethylene (46 %) and polyamide (33 %), although substantial variations in microplastic composition with both size category and location were found. These findings underline the importance of employing sampling and isolation techniques for microplastics from environmental samples that ensure the collection and quantification of smaller sized particles, which are easily missed. Failure to follow adequate protocols will result in severe risk of underestimating the actual extent of microplastic contamination and its potential environmental impact.