Measurement of soil-sebum partition coefficients for high molecular weight polycyclic aromatic hydrocarbons present at former gasworks, UK

The current research builds on the findings of a systematic literature review by the authors which recommends the need to work towards a standardised method for measuring the in vitro dermal absorption of HMW-PAH in soils. One part of the method is understanding the partitioning of the high molecular weight polycyclic aromatic hydrocarbons (HMW-PAH) from soil to sebum found in skin. In vitro HMW-PAH soil-sebum partition coefficients (KSS) were measured for twelve soils collected from former UK gasworks.  Concentrations of ∑16 USEPA PAH in the soils ranged from 51 to 1440 mg/kg, benzo[a]pyrene ranged from 3.2 to 132 mg/kg. Time series extractions (0.5, 1, 2, 4, 8 and 24 h) at skin temperature (32°C) of HMW-PAH from sebum to soil for two samples were conducted to determine the maximum release time-step. The maximum HMW-PAH release time-step was determined as 4 h, which was subsequently used as the extraction time for the remaining samples. Evaluation of KSS data for the 4 h extractions showed that soil type and selected HMW-PAH properties (literature based molecular weight and octanol-carbon partition coefficients) affect the amount of HMW-PAH released from soil into sebum. Characterisation of soil properties was limited to total organic carbon, which showed no relationship to KSS. Selected soils showed distinctly higher K¬SS than others. The relationship between MW and KSS was statistically significant while the relationship between KOC and KSS was not statistically significant. Further research effort is required to improve our understanding of which soil and HMW-PAH properties affect the release of HMW-PAH from soil into sebum and the reasons why.