Reproducibility, reliability, and regulatory relevance of plant visual injury assessments

Abstract

The registration of herbicides in the EU requires an assessment of risks to non‐target terrestrial plants (NTTP). Regulatory plant studies are performed to determine risk‐assessment‐relevant endpoints (50% effect rate) for quantitative parameters, mostly biomass and survival. Recently, EFSA stated that endpoints for qualitatively assessed plant visual injuries (PVI) such as necrosis, chlorosis etc. should be considered for the risk assessment as equal to endpoints derived from quantitatively determined parameters. However, the lack of guidance in the NTTP test guidelines on how to assess PVI and how to derive a statistically meaningful endpoint for PVI makes their use in risk assessments challenging. To evaluate and improve the reliability, reproducibility and regulatory relevance of PVI assessments in NTTP studies, the PVI Working Group was formed in 2022 within the SETAC Plant Interest Group. In a first exercise, research needs, guidance gaps and shortcomings in current methodologies were identified and are presented together with recommendations for a future, validated and harmonized method for assessment of PVI. Survey results revealed a high variability in how PVI are currently assessed, and that the reliability of this data is unclear. Under current conditions, the PVI data can rather be seen as supportive information instead of using it for the statistically‐sound determination of a regulatory endpoint. Consequently, standardization and harmonization of procedures for the assessment of PVI are needed. An improved scoring methodology should be developed which allows for a precise, statistically sound endpoint determination. Regarding regulatory relevance of PVI, further research is required to assess the biological meaning of PVI data and how this is connected to the regulatory requirements and protection goals. Last but not least, guidance is required on how to evaluate the historically available PVI data which is based on various assessment methodologies.