1.24 - Toxicology and Risk Assessment of Chemical Mixtures and Multiple Stressors

Abstract

This article is a continuation and update from the previous two editions which were published, respectively, in 1997 and 2010. Since the publication of the first book on Toxicology of Chemical Mixtures in 1994 (Yang, 1994a), we witnessed, with gratification, the advancement of science in this area, as well as the awareness and implementation of regulatory decisions by the United States Environmental Protection Agency (USEPA) and others to address issues of multiple chemical (and multiple stressor) exposures. Despite such impressive progress, however, if we focus on one of the examples cited in this article, a citizen’s petition on Jul. 17, 1984, under section 21 of Toxic Substances Control Act (TSCA), from Robert Ginsburg and Mary Ellen Montes, we are still far away from answering some of the questions concerning chemical mixture toxicology and risk assessment raised by these laypersons. Looking at another direction at CDC’s Fourth National Report on Human Exposure to Environmental Chemicals (CDC, 2009) and its related various updates up to the most recent one published in Feb. 2015 (CDC, 2015), neither do we have a satisfactory answer toward the question “What is the toxicological significance of the presence of at least 265 chemical pollutants (CDC, 2015) in our body?” Consider further the stressors that our bodies encounter, chemicals are but one of the multiple elements. The Gulf War Syndrome and, more recently, the potential negative environmental health impacts from unconventional oil and gas exploration (“Fracking”) all over the country, brought the significance of multiple stressors further into focus. Thus, we have a great deal of work and challenges ahead of us. While we face the challenges of this very complex and difficult area of toxicology and risk assessment of chemical mixtures and multiple stressors, new frontiers such as nanotechnology, nanotoxicology, e-cigarette, and others have arisen in recent years. In the meantime, a most significant endeavor and tremendous effort, the “Halifax Project” came into being, and its results, 12 review articles, appeared, in Jun. 2015, in a special supplemental issue of Carcinogenesis (Vol. 36, Supplement 1). Its emphasis on the low-dose, chronic exposures to mixtures of environmental pollutants on carcinogenesis based on the 11 Hallmarks of Cancer and its global contribution to the Toxicology and Risk Assessment of Chemical Mixtures and Multiple Stressors might prove to be a “Revolution” for science one day. Aspiring young scientists are encouraged to enter this vitally important area as we need talents from all disciplines of science to tackle these nagging problems.