Derivation of a site-specific assessment criterion for benzo[a]pyrene in red shale at a former coking works.

A former coking works in England is being remediated to enable its redevelopment. We have developed site specific human health risk assessment criteria (SSAC) for benzo[a]pyrene (BaP) based on detailed characterisation of red shale proposed for reuse in an area allocated for residential development. Samples of red shale were analysed using the Colon-enhanced Physiologically Based Extraction Test (CEPBET) to estimate the bioaccessibility of BaP. The results indicate that between 5% and 28% of the red shale BaP is bioaccessible. A cautious value of 50% was used in calculating an SSAC. The CLEA human health assessment model was used to calculate the SSAC and any changes to the default input parameters have been discussed and justified. Based on the fact that BaP appears to be a point-of-contact, rather than a systemic, carcinogen in animal studies, individual assessment criteria were estimated for the oral, inhalation and dermal routes of entry in-line with current UK guidance. An overall SSAC of 2.5 mg/kg for BaP in red shale for the residential with home-grown produce land use was then derived as the lowest of the three route-specific assessment criteria. This value is specific to both the site and the material being assessed. The approach adopted however can be applied on other sites and for other materials to inform detailed quantitative risk assessments.