Considerations for the inclusion of metabarcoding data into the plant protection product risk assessment of the soil microbiome.

There is increasing interest in further developing the plant protection product environmental risk assessment, particularly within the European Union, to include the assessment of soil microbial community composition, as measured by metabarcoding approaches. However, to date, there has been little discussion as to how this could be implemented in a standardised, reliable, and robust manner suitable for regulatory decision making. Introducing metabarcoding-based assessments of the soil microbiome into the plant protection product risk assessment would represent a significant increase in the degree of complexity of the data that needs to be processed and analysed in comparison to the existing risk assessment on in-soil organisms. The bioinformatics procedures to process DNA sequences into community compositional datasets currently lack standardisation, while little information exists on how this data should be used to generate regulatory endpoints and the ways in which these endpoints should be interpreted. Through a thorough and critical review, we explore these challenges. We conclude that currently, we do not have a sufficient degree of standardisation or understanding of the required bioinformatics and data analysis procedures to consider their use in an environmental risk assessment context. However, we highlight critical knowledge gaps and the further research required to understand whether metabarcoding-based assessments of the soil microbiome can be utilised in a statistically and ecologically relevant manner within a plant protection product risk assessment. Only once these challenges are addressed can we consider if and how we should use metabarcoding as a tool for regulatory decision making to assess and monitor ecotoxicological effects on soil microorganisms within an environmental risk assessment of plant protection products.