Dermal uptake of chemicals

摘要

Biomonitoring has revealed the signatures of hundreds of chemicals in human blood and excreta. Prevention of exposures, which is central to environmental health policy and practice, requires that relevant routes and pathways be understood. Some existing studies that encompass both environmental and biological monitoring provide the opportunity to test aggregate exposure models. A frequent outcome is a shortfall between predicted dose based on environmental measurements and apparent dose estimated from biomarker data. One possible explanation for under-prediction of dermal dose is direct use of results of batch absorption experiments expressed as fractional availability. Because fractional availabilities obtained in this manner are routinely less than those observed via inhalation or ingestion, dermal exposure has often been discounted. However, low apparent availabilities may be an artifact of poorly designed or interpreted experiments. Even low rates of chemical uptake via the skin can account for a non-negligible fraction of a biomonitoring-based dose estimate if exposure is chronic and involves substantial skin area. Regulatory initiatives such as REACH have fostered demand for methods for systematic evaluation of human exposures to commercial chemicals, including many found in consumer products applied directly to the skin. Given prior experience, reconsideration of traditional approaches to assessment of dermal exposure is necessary. Dermal absorption is described as gradient driven transport through a membrane. Observed shortfalls in specific aggregate exposure case studies provide a basis for evaluating physical constants needed to characterize dermal dose. Overall mass transfer coefficients reflecting total resistance to transport from the environment to clothing, from clothing to skin, and from the skin surface to systemic circulation can be generated from these studies and compared to estimates derived from understanding of component processes. Once adequate cases have been developed, chemical screening capability will be improved.