LONG-TERM EVALUATION OF POLYAROMATIC HYDROCARBON RETENTION IN FIELD-CONTAMINATED SOIL

Polyaromatic hydrocarbons (PAHs) exhibit hydrophobic properties contributing to easy adsorption on soil particles. Soils are thus natural reservoirs of PAHs due to the multitude of natural (e.g. volcanoes and forest fires) and anthropogenic (e.g. fossil fuel combustion, oil manufacturing and spills, wood preservation (creosote)) sources to the environment. This is intensified by partitioning into amorphous soil organic matter (humic substances) which also plays a significant role in retention of PAHs, and therefore contributes to their omnipresence. Of the hundreds of PAHs found in the environment, several are known or probable carcinogens and 16 are US EPA priority substances posing risks to human and ecosystem health. Potential also exists for transportation of soil PAHs into water bodies and possible re-suspension to the atmosphere. Nevertheless, data are scarce in literature concerning their retention and transfer in soils and little can be found with regards to soil-water partition coefficients and desorption/degradation processes and rates. Long-term changes in PAH soil concentration were evaluated using field-contaminated soil obtained from a 1-million-gallon spill of diluted bitumen into the Kalamazoo River near Ceresco, MI in 2010. Soil samples collected from the spill site after 5 years of remediation revealed the presence of 7 priority PAH substances in all samples. Replicate soil-water microcosms were then constructed and allowed to age under closed (anaerobic) conditions. Concentrations of PAHs in the soil and water were then analyzed after a 4-year incubation period and are again being analyzed after 7 years of incubation. Results show PAHs remain in measurable concentrations in soil and water, though concentrations decreased and only naphthalene and fluorene are found partitioned into the water fraction. Variability in PAH concentration was also shown to be influenced by grain size, with higher PAH retention in muddy and clay-rich soil fractions.