Chemical Mixtures: Considering the Evolution of Toxicology and Chemical Assessment

Abstract

The assessment of chemical mixtures is a complex topic for toxicologists, regulators, and the public. In this article the linkage between the science of toxicology and the needs of governmental regulatory agencies in the United States is explored through an overview of environmental regulations enacted over the past century and a brief history of modern toxicology. One of the goals of this overview is to encourage both regulators and scientists to consider the benefits and limitations of this science–regulatory relationship as they tackle existing issues such as chemical mixtures. It is clear that a) over the past 100 years chemical regulation and toxicologic research, have in large part, shared a common emphasis on characterization and regulation of individual chemicals. But chemical mixtures have been, and continue to be, evaluated at hazardous waste sites around the United States. For this reason the current U.S. Environmental Protection Agency guidelines for chemical mixtures assessment are also reviewed. These guidelines highlight the current practice of mixtures assessment, which relies primarily on the existing single-chemical database. It is also clear that b) the science and assessment of chemical mixtures are moving forward through the combined efforts of regulatory agencies and scientists from a broad range of disciplines, including toxicology. Because toxicology is at this exciting crossroads, particular attention should be paid to the forces (e.g., public demands, regulatory needs, funding, academic interests) that both promote and limit the growth of this expanding discipline.

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).…”

Zebrafish as a possible bioindicator of organic pollutants with effects on reproduction in drinking waters

“…So, different environmental chemicals may interact with each other and thereby induce weaker (antagonistic), additive or stronger (synergistic) combined effects than would be expected from single compounds (Monosson, 2005;Kortenkamp, 2007). In this sense, it must be highlighted that the knowledge of the impact of these chemical interactions is still insufficient (Monosson, 2005;Schwarzenbach et al, 2006;Kortenkamp, 2007;Holmstrup et al, 2010).…”

“…So, different environmental chemicals may interact with each other and thereby induce weaker (antagonistic), additive or stronger (synergistic) combined effects than would be expected from single compounds (Monosson, 2005;Kortenkamp, 2007). In this sense, it must be highlighted that the knowledge of the impact of these chemical interactions is still insufficient (Monosson, 2005;Schwarzenbach et al, 2006;Kortenkamp, 2007;Holmstrup et al, 2010). Moreover, the problem is exacerbated in drinking water from metropolitan areas, as the concentrations of emerging contaminants are low but numerous and variable over time (Westerhoff et al, 2005;Khetan and Collins, 2007;Kim et al, 2007), with municipal wastewater being the main source of most of these compounds (Metcalfe et al, 2003(Metcalfe et al, , 2014.…”

Chlorination by-products of bisphenol A enhanced retinoid X receptor disrupting effects

“…TEQ approach based on concentration addition model was introduced to perform the causality analysis [39]. There is no natural ligand for RXR␤ and BPA is the original chemical in the chlorination routine in the present study.…”