Comparison of Deposition Sampling Methods to Collect Airborne Microplastics in Christchurch, New Zealand

Airborne microplastics have been identified throughout the Northern Hemisphere in several studies. Synthesising measurements from multiple studies to derive a global distribution of airborne microplastics is difficult because no standard sampling protocol currently exists. Furthermore, measurements from the Southern Hemisphere are largely absent. We undertook a pilot study to test four different deposition samplers and their efficacy in collecting microplastics: a bottle with a funnel attached, an open beaker, a petri dish covered in double-sided adhesive tape and an automatic wet deposition collector. The four samplers were deployed to a suburban site in Christchurch, New Zealand, for four 6-day sampling periods. It was originally hypothesised that the funnel would improve sample retention by limiting resuspension; however, the open beaker was found to be similarly effective. We were unable to assess the effectiveness of the automatic wet deposition collector robustly due to low rainfall during the sampling periods. The adhesive tape sampler proved impractical. Particles collected from all samplers were inspected and classified as microplastics according to a visual screening criteria. Fibres, films, fragments and beads were identified, with fibres being the dominant morphotype (90%); however, only 10% of suspected microplastics were confirmed as plastic following μFTIR spectroscopy. Overall, we recommend the use of a funnel sampler or open beaker for future deposition studies. This is the first study of airborne microplastics in New Zealand and adds to a growing body of evidence as to the widespread nature of microplastics in the atmosphere.