Academic journal article Environmental Health Perspectives

Chemical Mixtures: Considering the Evolution of Toxicology and Chemical Assessment

Academic journal article Environmental Health Perspectives

Chemical Mixtures: Considering the Evolution of Toxicology and Chemical Assessment

Article excerpt

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 dear 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 dear 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. Key words: chemical mixtures, chemical regulation, mixtures assessment, risk assessment. Environ Health Perspect 113:383-390 (2005). doi:10.1289/ehp.6987 available via http://dx.doi.org/ [Online 21 October 2004]

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Toxicology is the workhorse science of numerous industries and regulatory agencies. By providing a more complete understanding of the toxic effects of chemicals, toxicology has also provided many societal benefits. Toxicology is used in the characterization and development of standards for regulation of natural and produced chemicals, ranging from those commonly used in food production to chemicals that may contaminant soil, water, or sediments at hazardous waste sites. It has been noted that most 20th-century toxicologic studies were primarily concerned with the effects of individual chemical exposures, laying the groundwork for the development of toxicology as a "single-chemical science." However, we are seldom if ever exposed to single chemicals; whether it is through our diet, pharmaceuticals, air, or our drinking water, we are exposed to mixtures of both anthropogenic and naturally occurring chemicals.

Members of communities located adjacent to hazardous waste sites or in industrial cities where they may receive exposure to hazardous chemicals through multiple sources are perhaps most acutely aware of their potential exposure to chemical mixtures. Often, in the United States, characterization of a hazardous waste site reveals multiple chemicals from multiple pathways resulting in a complicated matrix of chemicals and concentrations. For assessment purposes, the U.S. Environmental Protection Agency (EPA) defines chemical mixtures as either a) simple mixtures, containing "two or more identifiable components but few enough that the mixture toxicity can be adequately characterized by a combination of the components toxicities and the components interactions" or b) complex mixtures containing "so many components that any estimation of its toxicity based on its components' toxicities contains too much uncertainty and error to be useful" (U.S. EPA 2000).

Current methodologies for human health risk assessment commonly treat mixtures as simple mixtures, deriving the combined toxicity of individual components primarily from single-chemical studies. Community members active in monitoring waste site assessment and remediation question the adequacy of human health assessments based on a components approach. …

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