Standardizing microplastics used for establishing recovery efficiency when assessing microplastics in environmental samples

Reports of microplastic contamination in the environment are ever-increasing allowing for global assessments of their distribution and abundance. However, differences in sampling and analytical methods used to assess microplastic contamination vary among investigators, resulting in uncertainties when comparing or compiling data. The determination of recovery efficiency is one aspect of the assessment process that can mire comparability among investigations. We evaluated recovery efficiency among studies published in 2020 and found that appreciable variability existed concerning the density and size of the microplastics used in the recovery efficiency determinations. Further, the established recovery efficiency may not be reflective of that obtained with mixtures of microplastics found in environmental samples. Herein, we recommend that microplastic standards at least containing three types of polymer with different densities, three shapes, and a similar size to the detection limit, should be tested simultaneously when conducting analytical methods. The inclusion of such information will aid in the comparison of results among different investigations and will aid in assessing the global distribution of these contaminants.