Author(s)

M. Fay

Abstract

The Chemical Mixtures Program of the Agency for Toxic Substances and Disease Registry (ATSDR) studied the frequency of exposure to chemical mixtures at hazardous waste sites (HWSs) in the United States by analyzing contaminants found in completed exposure pathways (CEPs). CEPs are documented pathways in which exposure likely occurred. Data from 1,706 HWSs reveal that CEPs occurred at 743 (44%) of the sites. Of these, 588 sites had two or more substances in a CEP. Thus, exposure to mixtures occurred at 79% of the sites with exposure (588/743). However, sites often have more than 1 pathway, and pathways with a single contaminant are common. The number of exposure pathways with two or more chemicals is estimated to be approximately half of all CEPs. This estimate does not include exposure by multiple pathways, so the extent of exposure to mixtures might be higher than the estimate. Further analysis revealed that exposure to simple mixtures consisting of 3, 4, and 5 components occurred at 475, 390, and 321 sites, respectively. Although 2 chemicals constitute a mixture, 64% of the 743 sites had 3 chemicals in a CEP, 52% had 4 chemicals in a CEP, and 43% had 5 chemicals in a CEP. Exposure to mixtures by specific media was as follows: water, 413 sites; soil, 255 sites; air, 113 sites; and biota (mainly fish), 53 sites. Overall, water pathways had mixtures more often for lower numbers of chemicals (2 to 8 chemicals), but the number of sites with mixtures in soil pathways surpassed the counts for water at (and above) 9 chemicals in the mixture. The maximum number of chemicals in a CEP was 62. In conclusion, about four-fifths of U.S. HWSs with exposure pathways have chemical mixtures in a CEP, and, more importantly, about half of CEPs have a chemical mixture. Thus, exposure to mixtures of chemicals is quite common at HWSs. Keywords: hazardous waste sites, exposure, contaminants, chemical mixtures, combinations.

Keywords

hazardous waste sites, exposure, contaminants, chemical mixtures, combinations.