Biomonitoring as a tool in the human health risk characterization of dermal exposure

Dermal exposure is an important factor in risk characterization. In occupational settings it becomes relatively more important because of the continuous reduction in inhalation exposure. In the public health arena, dermal exposure may also form a significant contribution to the total exposure. Dermal exposure, however, is difficult to assess directly because it is determined by a host of factors, which are difficult to quantify. As a consequence, dermal exposure is often estimated by application of models for external exposure. In combination with modeled or measured data for percutaneous penetration, these provide an estimate for the internal exposure that is directly related to the systemic effects. The advantages and drawbacks of EASE (Estimation and Assessment of Substance Exposure) and RISKOFDERM (Risk Assessment of Occupational Dermal Exposure), two models for external exposure that are mentioned in the Technical Guidance Document for the European Union risk assessments performed under the Existing Substances Regulation (EEC/793/93), are discussed. Although new chemicals regulation (REACh, 1907/2006/EC) is now in place in the European Union, the principles applied under the previous legislation do not change and the same models will continue to be used. The results obtained with these models for styrene, 2-butoxyethanol, and 1-methoxy-2-propanol in specific exposure scenarios are compared with an alternative method that uses biomonitoring data to assess dermal exposure. Actual external exposure measurements combined with measured or modeled percutaneous penetration data give acceptable results in risk assessment of dermal exposure, but modeled data of external dermal exposure should only be used if no other data are available. However, if available, biomonitoring should be considered the method of choice to assess (dermal) exposure.