Application of measured in vitro dermal bioavailability of polycyclic aromatic hydrocarbons (PAH) in soil in detailed quantitative human health risk assessment

Our study shows that site-specific estimates of dermal exposure to selected polycyclic aromatic hydrocarbons contained in contaminated gasworks soil result in lower average daily exposure and risk to human health when compared to the generic assumptions used in risk assessment software. We use site specific in vitro dermal bioavailability flux (μg/cm²/h) for benzo[a]pyrene measured by earlier research published by the authors, where dermal flux provides an analogue of diffusion through the skin and into systemic circulation. We used measured in vitro dermal flux for gasworks contaminated soil containing 150 mg/kg of benzo[a]pyrene to estimate average daily exposure and risk using the Contaminated Land Exposure Assessment (CLEA) framework. Site-specific flux (0.00237 ng/cm²/hour) was used to calculate an uptake of 23.7 ng benzo[a]pyrene/m² skin/hour, resulting in an average daily exposure (ADE) ranging from 20.7 to 37.3 ng benzo[a]pyrene/kg bw/day for the first six years of a female child's life. The average ratio of average daily exposure to the Health Criteria Value (Index Dose) was 0.54, where a soil concentration of 278.4 mg/kg is equivalent to a ratio of ADE to Index Dose of one. The results show that for the dermal pathway only, the risk to human health calculated using site-specific dermal flux is lower than using default values used in CLEA. In our discussion we highlight that dermal bioavailability varies between sites and PAH and that differences are likely to be influenced by the source of contamination and the physico-chemical properties of soil. Our findings support an evidence-based shift toward sample-specific parameters in regulatory risk assessment frameworks, but the scalability, inter-laboratory reproducibility, range and contaminants tested and the cost-effectiveness of in vitro flux testing need to be researched further before broader regulatory adoption.