Background Total and Bioaccessible Concentrations of PAHs and Trace Metals in Two Florida Urban Soils.

Soil cleanup standards for contaminated soils can be based on either soil background concentrations or risk-based values. Polycyclic aromatic hydrocarbons (PAHs) are a group of contaminants come from biogenic, petrogenic and pyrogenic sources in the environment, with the majority remaining in soils and also often coexist with trace metals. The objective of this study was to determine the total background concentrations and distributions of PAHs and trace metals in Orlando and Tampa urban soils. However, mounting evidence suggests that understanding contaminant bioavailability in soils is necessary for accurate assessment of contaminant exposure to humans via oral ingestion pathway. Therefore, we also determined the bioaccessible concentrations of PAHs in those urban soil samples by n-butanol extraction method due to the relatively high concentrations of PAHs compared with trace metals. The results showed the soils were dominated by high molecular weight PAHs in both cities. Benzo(a)pyrene equivalent (BaP-EQ) concentrations in 60-63% samples were higher than residential Florida soil cleanup target level (FSCTL) and 20-25% samples were higher than industrial/commercial FSCTL in Orlando and Tampa. Orlando soils had relatively higher bioaccessible PAHs and BaP-EQ concentrations than Tampa soils, and both cities had similar PAHs bioaccessibility which ranged from 0 to 93%. High molecular weight PAHs had relative lower bioaccessibility than low molecular weight PAHs. In comparison, total trace metal concentrations were lower than the corresponding FSCTLs. No correlations were found between concentrations of metals and PAHs, with only V-Ni showing a strong correlation in both Orlando and Tampa soils. Based on molecular diagnostic ratios and PMF model, major sources of PAHs in both cities were similar, mainly coming from pyrogenic, traffic emissions, and biomass and coal combustion. Based on GIS maps, PAHs concentrations in central business district and areas near high traffic roads were significantly higher than the other areas in both cities.