Comparative Assessment of Vegetative and Reproductive Terrestrial Plant Species Endpoints from Exposure to Herbicides and Potential Environmental Implications: A Review

To investigate whether vegetative endpoints are protective of reproductive endpoints in terrestrial plant risk assessments (RAs) for authorization of plant protection products (PPPs), we assessed differences in sensitivity to herbicides between these parameters. Published literature and unpublished proprietary data generated for the registration of PPPs were used to compile a database. If reproductive endpoints were systematically more sensitive than the vegetative endpoints on which regulatory decisions are presently based, a concern could be raised about the protectiveness of the current RA process. Vegetative and reproductive endpoints were assessed considering further potentially relevant parameters. Reproductive endpoints were compared with vegetative endpoints of juvenile plants or with those of mature plants. Direct comparison by substance-species combination proved to be most adequate and was used to calculate quotients by effect level. In addition, we assessed the spread between different effect levels, estimating by which factor the conservatism would increase if effect rate (ER)50 endpoints were replaced by ER25 or ER10 endpoints with otherwise unchanged test parameters. Reproductive endpoints were found to be similarly sensitive as vegetative endpoints derived in nontarget terrestrial plant (NTTP) studies conducted following Organisation for Economic Co-operation and Development (OECD) or US Office of Chemical Safety and Pollution Prevention (OCSPP) guidelines. A switch from vegetative to reproductive endpoints would therefore not significantly change the conservatism (less than a factor of 1.5), whereas the change from ER50 to ER10 would (by a factor of ~5 to 6). However, because ecotoxicological tests on terrestrial plants bear intrinsic high variability that prevents the reliable detection of effects at the 10% effect level, ER10 endpoints are not a reliable basis for RA. No particular family, genus, or species with clusters of distinctly insensitive vegetative and sensitive reproductive endpoints could be identified that would call for regular testing of reproductive endpoints. Also, from the data set available, no specific herbicidal modes of action could be singled out for acting particularly on reproductive endpoints. Integr Environ Assess Manag 2020;16:166-183. © 2019 SETAC.