Keywords: 
• soil /
• total petroleum hydrocarbon /
• Alks components /
• PAHs components /
• toxic contributions /
• combined toxic effects

Abstract: The ecotoxicity of petroleum pollution in soil environment urgently needs to be addressed. The content and toxic characteristics of Alks and PAHs components in total petroleum hydrocarbon (TPH) exhibited significant differences, and their toxic contributions and combined toxic effects in TPH are not clear. In this study, using Vicia faba as the ecological receptor, the toxic effects of equivalent Alks and PAHs components in TPH ranging from 1 000 to 50 000 mg·kg^-1 were investigated. The impacts of equivalent hydrocarbon fractions on individual growth (germination rate, root length, root biomass, lateral root quantity, stem and leaf mass, chlorophyll content) and genetic levels (root tip mitosis, chromosomal aberration, micronucleus) of Vicia faba were assessed to explore the toxic effects and risk contributions in different TPH concentrations. The mixture toxicity index (MTI) method was used to calculate the combined toxic effects of Alks and PAHs components. Results indicated that the ecological toxicity of hydrocarbon components in TPH is influenced by their combined “chemical characteristics-dosage” interaction. As the germination rate of Vicia faba was used as a toxicity indicator, the toxic contribution of equivalent Alks components in TPH below 5 000 mg·kg^-1 was significantly higher than that of equivalent PAHs components; while the toxic contribution of PAHs components in TPH above 5 000~50 000 mg·kg^-1 was significantly higher than that of equivalent Alks components. While using the root quantity as the toxicity indicator, during the early growth stage of Vicia faba (0~7 days), the equivalent PAHs in TPH ranging from 1 000 to 50 000 mg·kg^-1 exhibited stronger toxicity, while there was no significant difference in toxicity between Alks and PAHs during the later growth periods (7~14 days). Genetic toxicity results showed that equivalent PAHs components in TPH ranging from 1 000 to 50 000 mg·kg^-1 were more toxic than equivalent Alks components. At the individual level, the equivalent Alks component was the most sensitive to the root quantity of Vicia faba, and its toxicity threshold was 1 120.6 mg·kg^-1, and the corresponding TPH concentration was 11 672 mg·kg^-1. The equivalent PAHs component was the most sensitive to the germination rate of Vicia faba, and its toxicity threshold was 2.61 mg·kg^-1, and the corresponding TPH concentration was 15 353 mg·kg^-1. At the cellular and genetic levels, when mitotic index (MI) was used as the toxicity indication endpoint of the component hydrocarbons, the TPH concentrations corresponding to the toxicity thresholds of the equivalent Alks and PAHs were about 45 000 mg·kg^-1.The MTI results indicated that the combined toxicity of Alks and PAHs components in TPH ranging from 1 000 to 10 000 mg·kg^-1 exhibited a synergistic effect, while the toxicity of Alks and PAHs components in TPH ranging from 20 000 to 30 000 mg·kg^-1 complicated combination effects on various toxicity endpoints. When the TPH content amounted to 50 000 mg·kg^-1, the combined toxicity of Alks and PAHs components mainly exhibited an antagonistic effect. The results revealed that the toxicity of Alks components should be paid attention when TPH content was below 5 000 mg·kg^-1. On the contrary the PAHs components have a more important influence on plant growth and genotoxicity when TPH content was over 5 000 mg·kg^-1. This study provided theoretical basis for the toxicity risk assessment of petroleum-contaminated sites.