Halogenated aromatic hydrocarbons and toxicity equivalency factors (TEFs) from the public health assessment perspective

Public health guidance values for chemical mixtures: current practice and future directions

Agency for Toxic Substances and Disease Registry (ATSDR) utilizes chemical-specific minimal risk levels (MRLs) to assist in evaluating public health risks associated with exposure to hazardous substances. The MRLs are derived based on the data compiled from current worldwide literature searches and presented in ATSDR's toxicological profiles. These documents profile not only individual chemicals, but also groups of chemically related compounds and chemical mixtures. ATSDR took several approaches when developing MRLs for chemical mixtures. In some instances, toxicity equivalency factors were used to estimate the toxicity of the whole mixture; in other instances, the most toxic chemical was assumed to drive the health assessment for the whole mixture. Another approach was to treat the mixture as one entity and develop a health guidance value for the whole mixture. In yet another approach, each chemical of the mixture was evaluated separately and several health guidance values were developed. In the future, ATSDR will evaluate priority chemical mixtures found at hazardous waste sites. A weight-of-evidence approach, physiologically based pharmacokinetic modeling and bench-mark dose modeling, and quantitative structure-activity relationships will have an impact on the development of MRLs and the assessment of chemical mixtures.

Breast-feeding exposure of infants to environmental contaminants--a public health risk assessment viewpoint: chlorinated dibenzodioxins and chlorinated dibenzofurans

Exposure of children to chlorinated dibenzodioxins and chlorinated dibenzofurans via breast-feeding has been well-documented in industrialized countries. Recent studies indicate a possible link between development of subtle health effects in children and their exposure to dioxin-like chemicals from maternal milk. Some examples of the effects are lower vitamin K levels, increased thyroxine levels, and mild changes in liver enzymes. The projected daily intakes of chlorinated dibenzodioxins and chlorinated dibenzofurans are compared with minimal risk levels for intermediate duration oral exposure (15-365 days) derived for these chemicals. Public health recommendations for future actions related to infant intake of chlorinated dibenzodioxin- and chlorinated dibenzofuran-contaminated breast milk are also addressed.