Solving the non-alignment of methods and approaches used in microplastic research in order to consistently characterize risk

, Koelmans Albert, Redondo Hasselerharm Paula, Mohamed Nor Nur Hazimah, Kooi Merel.

The lack of standard approaches in microplastic research caused deficiencies in the comparability of data across methods used, locations, biota and environmental compartments. This limits the development of monitoring and risk assessment frameworks, which in turn limits progress in the abatement of plastic pollution. An obvious solution is harmonization of methods, which is ongoing and crucial, however is slow and laborious. We suggest that some of the most pressing problems can also be reduced by pragmatic rescaling methods that are able to improve the alignment of methods used in microplastic research. First, we describe a method to correct for the differences in size ranges as used by studies reporting microplastic concentrations, and demonstrate how this reduces the variation in aqueous phase concentrations caused by method differences. Second, we provide a method to convert number, volume and mass concentrations into one another using probability density functions that represent environmental microplastic. Finally, we use this method to correct for the incompatibility of data as used in current species sensitivity distributions (SSDs), caused by differences in the microplastic types used in effect studies and those in nature. We derived threshold effect concentrations from such a corrected SSD for freshwater species. Comparison of the rescaled exposure concentrations and threshold effect concentrations reveals that the latter would be exceeded for 1.5% of the known surface water exposure concentrations of surface waters worldwide. Altogether, this tool set allows us to correct for the diversity of microplastic, to address it in a common language, and to assess its risks as one environmental material.

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