Estimating Fifty Percent Effect Rates for Plant Visual Injury

The authorization of plant protection products (PPP) in the EU requires an assessment of potential impacts on non-target terrestrial plants (NTTP) occurring outside the treatment area based on results of regulatory tests. Specific guidelines (OECD 208 (2006a) and OECD 227 (2006b)) provide general test designs and define the measuring parameters, however there is some ambiguity in both endpoints required and procedures. Seedling emergence (as applicable), survival, and biomass are parameters that are quantitatively assessed, while plant visual injuries (PVI) (chlorosis, necrosis, wilting etc., as examples) are based on subjective and non-standardized observations, making them less suitable for producing reliable and objective outcomes for regulatory purposes. In the European Union, the ER50 is used to assess the risk of PPPs on NTTPs by comparing it to the predicted exposure of NTTP in the field. Recently, ER50 values derived from PVI in the risk assessment has been requested if it is lower than that of other endpoints (Central zone steering committee 2021). This guidance stems from observations made by the EFSA PPR Panel in 2014, where it was noted that in a significant number of cases, the PVI endpoint was reported as lower than other endpoints. In order to address this request, the PVI Working Group (WG) within the SETAC Plants Interest Group is aiming to foster harmonization in PVI assessments, ultimately strengthening the environmental impact assessments for PPPs and the protection of NTTP. It has to be noted that PVI are based on subjective and non-standardized observations. Recently, EFSA requires that ER50s for qualitatively assessed PVI should be considered for the risk assessment as equal to endpoints derived from quantitatively determined parameters. However, the interpretation of the data in terms of an ER50 is related to several challenges as it has been discussed previously (Fellman et al; 2023; IEAM). Furthermore, there is no guidance available harmonizing the assessment method of PVI and the statistical interpretation of the data leading to a multitude of approaches being used. Regulatory Authorities from across the globe have attempted to provide some insight into methods used to evaluate endpoints for differing scoring systems (UBA, EFSA, USEPA. RIVM, HAWC) but no agreement has been reached so far. The PVI SETAC Working Group under the umbrella of the SETAC Plants Interest Group aims to harmonize the statistical analysis of PVI data by addressing the various PVI assessment methods used in regulatory NTTP effect studies.