Comparative study between CalTOX and soil screening levels modeling approaches

A comparison was made between two different approaches to environmental modeling and risk assessment, specifically the one-medium approach of the USEPA Soil Screening Levels (SSL) and the multimedia approach in the CalEPA (CalTOX), Eleven priority pollutants were selected to represent different classes of chemicals as per their toxicity physical and chemical properties, and persistence in the environment Benzene, dioxin, PCB B(a)P, chlordane, chloroform, and TCE represent carcinogens, while xylene, toluene, phenol, chlordane, pyrene, TCE, and chloroform represent noncarcinogens. The highly volatile contaminants, including benzene, chloroform, xylene, toluene, and TCE, were selected to compare the volatilization from soil and the significance of inhalation pathways of the two models. The contaminants with strong sorption to soil and dust particles (dioxin, B(a)P, PCB, and chlordane) exhibited a preferential soil ingestion pathway. In contrast with CalTOX, inhalation was not considered as the dominant pathway for all the volatile contaminants in SSL. Furthermore, the risk assessment component of CalTOX accounts for multiple pathways as a consequence of its multimedia representation. Because the two models were based on different approaches, it is expected that the results would be different. For example, the results of the SSL were more conservative compared with CalTOX for all 1 chemicals. This observation still holds when considering the total risk from CalTOX vs. the risk based on the dominant pathway in SSL. Finally, the cancer slope factors and references doses were not the same for all the chemicals used in this study and resulted in different risk estimates.