Predicting hormesis in mixtures of herbicidal compounds – where are we and how far can we go?

Authors: BELZ, REGINA - University Of Hohenheim; Duke, Stephen

Submitted to: Julius Kühn Archiv
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/18/2018
Publication Date: 1/18/2018
Publication URL: https://handle.nal.usda.gov/10113/6477315
Citation: Belz, R.G., Duke, S.O. 2018. Predicting hormesis in mixtures of herbicidal compounds – where are we and how far can we go? Julius Kühn Archiv. 458:161-167.
DOI: https://doi.org/10.5073/jka.2018.458.023

Interpretive Summary: Hormesis is the stimulatory effect of a subtoxic dose of a toxin. We know very little about the hormetic effects of herbicides, especially when more than one is used, as is commonly practiced. This paper summarizes approaches to successes in predicting hormesis of herbicide mixtures.

Technical Abstract: Predicting the occurrence and expression of stimulatory effects of subtoxic doses of phytotoxins or herbicides (hormesis) in mixtures is a challenging and needed task, considering that herbicide exposures in practice often occur in mixtures at low doses due to drift deposition, errors in application, protection by mulch, herbicide resistance, small-scale dose heterogeneity, and other causes. While joint effects in toxin mixtures can be straightforwardly modeled and predicted at toxic doses, the evaluation at stimulatory doses lacks a straightforward statistical approach. Prediction of effective hormetic doses can be adequately facilitated by adopting joint-action models that have been developed for the inhibitory dose range. In contrast, prediction of the magnitude of hormesis as one of the most interesting quantitative features of hormesis is not so easy. Currently, there are no mechanistic models available that could be adopted to predict the magnitude in mixtures nor is there a generally accepted model available. Nevertheless, some promising attempts were made to predict the hormetic magnitude in herbicidal mixtures demonstrating the fundamental possibility of modeling hormesis in mixtures and providing valuable insights into the phenomenon. The success of these attempts are summarized, and future research needs and limits are discussed.