Distribution Characteristics and Toxicity Equivalent of Polycyclic Aromatic Hydrocarbons in Different Soil Fractions of Long-term Contaminated Soils
Soil organic matter(SOM)plays a crucial role in influencing the environmental behavior of polycyclic aromatic hydrocarbons(PAHs)in soil.The content and structure of SOM in different soil components may vary,leading to different capabilities of PAH enrichment and environmental risks.Using a combination of density and particle size fractionation methods,the SOM in four long-term con-taminated soils was divided into three fractions:light fraction organic matter(LF),coarse mineral-as-sociated organic matter(CMAOM)(>53 μm),and fine mineral-associated organic matter(FMAOM)(<53 μm).The distribution characteristics of 15 PAHs in these organic matter fractions were investigated,and the environmental risks of PAHs in LF,CMAOM and FMAOM were assessed using the toxicity equivalent concentration of benzo[a]pyrene(TEQBaP).The results showed that the total contents of 15 PAHs ranged from 3.78 to 16.96 mg·kg-1 in the four soils.The total concen-tration of PAHs in LF ranged from 128.23 to 355.78 mg·kg-1,which was 9.5 to 36.2 times and 14.2 to 71.3 times higher than those in CMAOM(3.55 to 19.28 mg·kg-1)and FMAOM(1.80 to 13.83 mg·kg-1),respectively.Although LF accounted for only 0.5%to 3.5%of the soil mass,the enriched PAHs in LF accounted for 12.3%to 61.8%of the total PAHs in the bulk soil.Different SOM fractions exhibited variations in their capabilities of PAHs enrichment,but the composition of the enriched PAHs was similar.Among the organic matter fractions,LF had the highest TEQBaP value for PAHs,which was 9.7 to 35.3 and 14.7 to 79.7 times higher than those in CMAOM and FMAOM,respectively.LF organic matter in soil has a relatively fast turnover rate,leading to relatively higher environmental risks of the associated PAHs.Therefore,special attention should be paid to the PAHs associated with LF during the environmental risk assessment and remediation of PAH-contaminated soil.
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