Risk assessment of residual gasoline components in unsaturated soils

There is no question about the importance of understanding the fate of oil pollutants and the risks of individual components of gasoline to human health. To investigate the effects of major environmental factors on the volatilization of regular gasoline from unsaturated soils, a series of experiments were organized and performed on four typical Japanese soils under different temperature, soil organic matter content, and water content conditions. Quantitative assessment of risks of each residual gasoline component to human health was pioneered using the experimental results and a self-developed software program, Geo-Environmental Risk Assessment System (GERAS). Results of this study illustrated that (1) temperature and soil organic matter had significant effects on volatilization and thus on the residual concentrations of gasoline components remaining in unsaturated soils. These residual concentrations were positively related to the amount of soil organic matter, but inversely related to temperature. (2) Risks of residual gasoline components remaining in soils depended on exposure pathway, gasoline component, and carbon numbers. Risks of respiratory exposure due to vapor inhalation were generally higher than the risks of oral exposure due to intake of crops and water. (3) Although residual concentrations of gasoline components remaining in soils with high organic matter contents were high, their risks to human health were low. This is because high organic matter content has strong sorptivity for gasoline components, resulting in less vapor inhalation, less intake from water, and low bioavailability for crops.