Measuring and Reducing Bioavailability of PAHs in Soils

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are a group of organic contaminants that are widely distributed in soils. Some PAHs are potent human carcinogens. When released into soils, PAHs are often emitted within a certain source matrix (e.g. soot, coal tar or oils). In addition to the diversity of the PAH source matrix, soils are also very heterogeneous mixtures containing many different components, such as sand, clay, organic matter and black carbon which can have varying capacity and affinity for sorbing hydrophobic organic contaminants. Together, these different matrices in soil control the PAH bioavailability to receptors such as soil invertebrates and human beings via various exposure pathways. In terms of soil remediation, numerous recent studies have demonstrated the prominent effectiveness of condensed, black carbon particles, such as biochar or activated carbon (AC), in reducing the bioavailability of hydrophobic contaminants in ecological receptors. The primary objective of this research was to investigate how different PAH source materials and geochemical soil components interact with each other and affect the overall sorption capacity for PAHs and the freely dissolved concentrations measured by passive samplers. Subsequently how these interactions can further affect the uptake of PAHs by both ecological receptor, such as soil invertebrates, as well as human beings through dermal contact and incidental ingestion of contaminated soils are investigated. For each of these exposure pathways, equilibrium and kinetic models have been developed to explain and predict PAH bioavailability to different receptors. The performance of the models has been evaluated under different source materials. In general, these models can give adequate predictions of PAH bioavailability with deviation falling within one log unit when evaluated across a wide range of soil concentrations. In terms of soil remediation, biochar amendment has exhibited promising and varying effectiveness in reducing PAH bioavailability from soils to different receptors. The effectiveness also varies with different source materials.