Assessing and mitigating simulated population‐level effects of 3 herbicides to a threatened plant: Application of a species‐specific population model of Boltonia decurrens

Abstract

Extrapolating from organism-level endpoints, as generated from standard pesticide toxicity tests, to populations is an important step in threatened and endangered species risk assessments. We apply a population model for a threatened herbaceous plant species, Boltonia decurrens, to estimate the potential population-level impacts of 3 herbicides. We combine conservative exposure scenarios with dose-response relationships for growth and survival of standard test species and apply those in the species-specific model. Exposure profiles applied in the B. decurrens model were estimated using exposure modeling approaches. Spray buffer zones were simulated by using corresponding exposure profiles, and their effectiveness at mitigating simulated effects on the plant populations was assessed with the model. From simulated exposure effects scenarios that affect plant populations, the present results suggest that B. decurrens populations may be more sensitive to exposures from herbicide spray drift affecting vegetative stages than from runoff affecting early seedling survival and growth. Spray application buffer zones were shown to be effective at reducing effects on simulated populations. Our case study demonstrates how species-specific population models can be applied in pesticide risk assessment to bring organism-level endpoints, exposure assumptions, and species characteristics together in an ecologically relevant context. Environ Toxicol Chem 2018;37:1545-1555. © 2018 SETAC.

Effects of herbicides on non-target plant species diversity and the community composition of fallow fields in northern China

“…With this in mind, more attention should be paid to the prevention and control of the ecological risks of low concentrations or sublethal doses of herbicides in agricultural landscapes, which are often caused by herbicide drift and runoff from sprayed fields into adjacent non-target areas 44,54 . A certain width of herbicide-free isolated areas could be maintained between farmlands and non-target areas to controls ecological risks 55 .…”

Adapting population models for application in pesticide risk assessment: A case study with Mead's milkweed

“…We limited the exposure–effects relationships to exposures from spray drift and effects on vegetative vigor for the present study. Spray drift of the 2 example herbicides, atrazine and mesotrione, results in higher predicted exposure levels adjacent to the application compared with runoff, and tested plants were more sensitive to both compounds in vegetative vigor compared with seedling emergence studies (Schmolke et al ). Accordingly, spray‐drift exposure affecting vegetative vigor was identified as the most important exposure route in the context of the 2 example herbicides.…”

“…The exposure level in the bin representing 18‐ to 20‐m distance to the treated area was used as the “tail” exposure for all distances >20 m. Maximum application rates according to the label for atrazine and mesotrione (2 and 0.24 lb/A or 2242 and 269 g/ha, respectively) were used for the estimation of exposure patterns applied. A more detailed description of the estimation of exposure levels across the assumed habitat area as well as the applied exposure patterns can be found in the Supplemental Data and in Schmolke et al ().…”

“…Dose–response relationships for survival rates and shoot dry weights (representing impacts on vegetative growth) were applied in the present model. A more detailed description of the dose responses applied is provided in the Supplemental Data and in Schmolke et al ().…”

“…Statistical significance between model simulations of different scenarios (i.e., data collected under different conditions) can generally be achieved by an arbitrarily high number of repetitions (White et al ) and does not provide information about the magnitude of the difference between scenarios simulated with the model. In the present study, we defined a reduction in average population size by 5% compared with untreated controls as a “relevant” effect size (Schmolke et al ).…”