Human Aryl Hydrocarbon Receptor Ligand Activity of 31 Non-substituted Polycyclic Aromatic Hydrocarbons as Soil Contaminants

Toxic equivalency factors (TEFs) of 31 non-substituted polycyclic aromatic hydrocarbons (PAHs) for the human aryl hydrocarbon receptor (AhR) ligand activity were measured using the yeast recombinant reporter gene assay established by Miller et al., in order to estimate the toxic equivalents of individual PAHs in environmental samples. Ten PAHs showed sigmoid-shape concentration-response curves. An effective concentration to achieve 50% activity obtained with 1 μmol/l benzo[a]pyrene (BaP) (EC50BaP) was calculated by curve fitting, and TEFs were calculated from the ratio of EC50BaP for BaP to that for the chemical studied. The highest TEF was found for naphthacene (NPC) (TEF=35) followed by benzo[b]fluorene (BbFl) (19), benzo[k]fluoranthene (BkF) (11), benz[a]anthracene (BaA) (7.0), benzo[j]fluoranthene (BjF) (4.0), benzo[a]fluorene (BaFl) (1.9), benzo[b]fluoranthene (BbF) (1.4), chrysene (CHR) (1.1), and BaP (1.0). Concentration dependent activities were also observed for indeno[1,2,3-cd]pyrene (IP) and fluoranthene (FLT). The TEFs of IP and FLT were about 0.2 and 0.02, respectively. The other 19 PAHs, naphthalene (NPT), acenaphtylene (ACL), acenaphthene (ACT), fluorene (FLU), anthracene (ANT), phenanthrene (PHN), pyrene (PYR), triphenylene (TRI), benzo[e]pyrene (BeP), perylene (PER), benzo[ghi]perylene (BgP), dibenz[a, h]anthracene (DahA), picene (PIC), coronene (COR), dibenzo[a, e]pyrene (DaeP), dibenzo[a, h]pyrene (DahP), dibenzo[a, i]pyrene (DaiP), dibenzo[a, l]pyrene (DalP) and naphtho[2,3-a]pyrene (NaP), showed little or no activity in the 0.1-1,000 nmol/l range. The toxic equivalents (TEQs) of surface soil were calculated by multiplication of the TEFs with the concentrations in soil samples collected from Kyoto, Japan. The TEQ of BaA showed the highest value of the 16 US Environmental Protection Agency Priority Pollutant PAHs.