Challenges in Regulating Pesticide Mixtures

Abstract

ABSTRACT. This paper introduces the field of mixture toxicity and the challenges in regulating pesticide mixtures. Even though pesticides are unique chemical stressors designed to have biological activity that can affect a number of nontarget species, they are intentionally placed into the environment in large quantities. Currently, methods and terminology for evaluating mixture toxicity are poorly established. The most common approach used is the assumption of additive concentration, with the concentrations adjusted for potency to a reference toxicant. Using this approach, the joint action of pesticides that have similar chemical structures and modes of toxic action can be predicted. However, this approach and other modeling techniques often provide little insight into the observed toxicity produced by mixtures of pesticides from different classes. Particularly difficult to model are mixtures that involve a secondary toxicant that changes the toxicokinetics of a primary toxicant. This may result in increased activation or a change in the persistence of the primary toxicant within the organism and may be responsible for a several-fold increase or decrease in toxicity. At present, the ecological effects caused by mixtures of pesticides are given little consideration in the regulatory process. However, mixtures are being considered in relation to human health in the pesticide registration process, setting a precedent that could be followed for ecological protection. Additionally, pesticide mixtures may be regulated through toxicity testing of surface water under the Clean Water Act. The limits of our basic knowledge of how mixtures interact are compromising both these avenues for regulating mixtures. We face many challenges to adequately protecting the environment from mixture toxicity; these challenges include understanding the interactions of toxicants within an organism, identifying the mixtures that most commonly occur and cause adverse effects, and developing a regulatory structure capable of minimizing environmental impacts.

Time- and Dose-Dependent Effects of Roundup on Human Embryonic and Placental Cells

“…As Roundup was more active than its claimed active ingredient in all instances, the formulation adjuvants probably allow a better cell penetration and stabilization of the product. Chemical mixtures in formulations may thus be underestimated regarding their toxic or hormonal impact (Tichy et al 2002, Lydy et al 2004, Monosson 2005. Most of the tests undertaken in a regulatory context are in fact performed with the active ingredient alone in vivo for one or two years (Williams et al 2000).…”

Cholinesterase and glutathione‐S‐transferase activities in freshwater invertebrates as biomarkers to assess pesticide contamination

“…These additive models are useful when the effect of the combined chemicals can be estimated directly from the sum of the concentrations of the constituent toxicants or from the sum of the observed biological responses. However, sometimes measured toxicity does not match predicted toxicity because antagonistic or synergistic chemical interactions influence the toxicokinetics of the constituent compounds [82]. To understand interactions, Belden et al [83] suggested the model of simple interaction where it is assumed that one of the toxicants influences the toxicity of the other toxicant through an indirect mechanism.…”

Incorporating the joint toxicity of co‐applied pesticides into the ecological risk assessment process

“…Although environmental mixtures occasionally can be composed of multiple contaminants, most of these compounds are at much lower TUs as compared to the most potent components that are likely the drivers of toxicity (Belden et al 2007b;Trimble et al 2009). Potential environmental mixtures in which toxic components vary greatly from site to site and each active ingredient is registered to different agrochemical companies will profoundly increase complexities of the assessment (Lydy et al 2004). …”