Keywords: 
• PAHs /
• toxicity evaluation /
• risk assessment

Abstract: Toxicity evaluation is an important part in human health risk assessment. Two methods were most used for toxicity evaluation:1) method one (method 1) uses BaP carcinogenic slope factor as indicator after converting PAHs to BaP equivalents; 2) method two (method 2) directly utilizes parameters related to PAHs such as PAHs carcinogenic slope factors and PAHs non-carcinogenic reference doses. However, during PAHs human health risks calculation process, little study has been done about the differences between the above methods. Layered soil health risk assessment models using both method 1 and method 2 were conducted in a PAHs contaminated coking plant in the south of Jiangsu Province. PAHs risks, remediation pollutants and volumes were compared, and the key factors causing the above differences were discussed. Results showed that with methods 1 and 2, the maximum carcinogenic risks and remediation volumes for surface soils within 1.0 m depth were 1.48E-05 and 1.32E-05, 27 846 m³and 28 667 m³respectively, and the remediation pollutants were BaP and Acy. For soils within 1.0~3.0 m depth, the maximum carcinogenic risk calculated by method 1 was 3.36E-08, indicating no need to repair; however, the maximum carcinogenic risk and non-carcinogenic hazard index calculated by method 2 were 3.73E-04 and 6.96E+01 respectively, and the remediation volumes were 35 944 m³with Nap as major remediation pollutant. Overall, the total remediation volumes 64 611 m³calculated with method 2 is 2.45 times more than that of 27 846 m³ calculated with method 1, since method 1 underestimated the risks of high volatile PAHs especially NaP in deep soils. Therefore, method 2 should be recommended in PAHs health risks assessment from the conservative perspective.