Seeking solutions to chemical mixtures challenges in public health.

The Agency for Toxic Substances and Disease Registry (ATSDR) identifies people near hazardous waste sites who are at potential health risk because of their exposure to environmental chemicals. Nearly, 2000 chemicals have been associated with such sites. Residents of U.S. communities are potentially exposed to hazardous substances through air, soil, drinking water, and food. The agency has determined that more than 73 million people live within a 4-mile radius of waste sites. More than 14 million Americans live within 1 mile of a National Priorities List site, of which 11% are 7 years of age or younger, 12% are 64 years of age or older, 24% are women of childbearing age, and 25% are minorities. The lack of adequate environmental sampling and information on human exposures often restricts ATSDR's evaluation and assessment activities. Assessing human exposure with its attendant health risks and outcomes is complex because many populations have a wide range of reported illnesses, and generally exposures are to mixtures of chemicals. This prompted ATSDR to consider mixtures issues more in depth and to establish a formal mixtures assessment and research program in 1994. In this paper, we present an overview of the agency activities, the genesis, legislative mandates, and pertinence of the mixtures program including applied research and the development of methods for evaluating the impact of multiple-chemical exposure. On the basis of 20-year experience of evaluating and researching environmental chemical mixtures at waste sites, ATSDR convened the International Conference on Chemical Mixtures (ICCM) in 2002. The conference was supported by several federal agencies and scientific organizations and attended by international and national experts. The conference addressed broad topics such as prevalence of exposures to chemical mixtures, importance of interactions at environmentally relevant levels, validity of assuming additivity (dose or response) as default for mixtures assessment, and promising avenues in the three broad areas, viz., research, assessment, and computational tools.