Grab vs. neuston tow net: a microplastic sampling performance comparison and possible advances in the field

Abstract

With the rapid evolution of microplastic research over several decades, there is an urgent need to compare methodologies for quantifying microplastic in aquatic environments. The most common method for sea surface sampling is a neuston net tow. This method captures microplastic from large water volumes, and although is widely employed, it is specifically designed for studying plankton ecology. Its effectiveness for microplastic research is limited by the net's mesh size as well as the likelihood of contamination. In our study, we compared a 1 L surface grab sampling method to a 335 μm neuston net tow. Grab sampling collected over three orders of magnitude more microplastic per volume of water as well as a smaller size range and greater proportion of non-fibrous plastic than sampling with a neuston net. Consequently, solely relying on neuston net samples appears to result in an underestimation of the extent of microplastic pollution. For studies aiming to capture and sort larger microplastics without a microscope, the neuston tow method is preferred, since it samples a greater volume of water, increasing the potential of capturing microplastic pieces. Grab sampling can capture plastic at the micro- and nano-scale and in environments where neuston nets are impractical, but the small volume of water sampled may result in high variability among samples. The comparison of these techniques comes at a critical time when sampling methods need standardization for the accurate measurement of the distribution and composition of microplastic in aquatic environments worldwide.