A meta-analysis of methodologies adopted by microplastic studies in China.
China is the world's largest plastic producer and has been a focus of research on microplastic pollution. An increasing number of studies have documented plastics in the sediment, water and biota of China over the past decades. This systematic review compares different methodologies adopted by microplastic studies in China, including sampling equipment and methods; laboratory procedures in microplastic extraction and identification; and the characterisation and quantification of particles. In general, sediment samples were primarily collected with a grab sampler, while water samples were mostly taken from the surface using trawl nets. Different techniques, including density separation, chemical digestion, sieving and filtration, were applied to extract microplastics from the sample matrix. Visual sorting was an obligatory step that identifies microplastics by their morphological characteristics, such as size, shape and colour. Most studies in China reported the prevalence of irregular-shaped particles with sizes smaller than 1 mm. The chemical properties of microplastics were also assessed using infrared and Raman spectroscopy. Quantitative units commonly used for sediment, water and biota samples were "items per kg", "items per m3" and "items per individual", respectively. The inconsistencies in methods have marked the urgent warrant of a standardised methodology. It is believed that the findings of the present review can serve as an important waypoint contributing towards a more efficient and long-acting methodology for microplastic research, that can enable meaningful inter-study comparisons.