Multiple-time Addition Of Benzo(a)Pyrene And Phenanthrene In Soils Impact Its’ Toxicological Effects On Earthworms

Polycyclic aromatic hydrocbarons (PAHs) are unique classes of pollutants which constitute of hundreds of individual substances. PAHs contain two or more fused aromatic rings which were made up of carbon and hydrogen atoms. The behaviors and fates of PAHs are of increasing concerns, due to the nature of non-degradable、persistent and carcinogenic、tumorigenic and mutagenic properties. The availability of polycyclic aromatic hydrocarbons in soil is an important parameter for risk assessments.The exposure experiments with different aging times of B[a]P and Phe (1,714,28, and 56 days) were conducted to analyze the contents of B[a]P and Phe in soil by chemical solvent (accelerated solvent extraction, ASE) and Tenax extraction (the available fraction) methods in both the multiple-time and one-time addition method. Earthworms were exposed to soils with different treatments of B[a]P and Phe, the amounts of B[a]P and Phe enriched in earthworm, the neural red retention time, the micronucleus rates and glutathione-S-transferease activities in coelomocytes of earthworm were also measured. The main results are as follows:The contents of the available B[a]P and Phe sharply declined in the first 28d (0-28 d), and then slowly decreased between 28 d and 56 d in both the multiple-time and one-time addition treatments. The contents of the available B[a]P in soil were lower by 12.84%-69.31%(P<0.05) than that in the one-time addition treatment; and the contents of the available Phe in soil were lower by 35.13% to 96.97%(P< 0.05) than that in the one-time addition treatment, respectively.The amounts of B[a]P and Phe enriched in earthworms rapidly declined in the first 28d (0-28 d), and then slowly decreased between 28 d and 56 d in both the multiple-time and one-time addition treatments. The very significantly positive correlations (R2= 0.8614, p< 0.01; R2= 0.8529, p< 0.01) between the amounts of B[a]P and Phe accumulated in earthworms and the contents of B[a]P and Phe extracted from soil by Tenax was found, and these correlations are higher than those (R2= 0.7987, p< 0.01; R2= 0.6891, p< 0.01) between the amounts of B[a]P and Phe accumulated in earthworms and the contents of B[a]P and Phe extracted from soil by ASE. This showed that the quantities of Tenax extractable BaP and Phe from soil are more suitable for forecasting the bioavailability of BaP and Phe in soil.The GST activities in earthworms and the micronucleus rates in earthworm coelomocytes sharply declined in the first 28d (0-28 d), and then slowly decreased between 28 d and 56 d in both addition methods. While the NRRT in earthworm coelomocytes greatly increased in the first stage, and then slowly decreased in the following incubation time in both addition methods. The activities of GST in earthworm under the B[a]P multiple-time superimposed pollution were ranged from 6.50%-34.51%, which were lower than that in the one-time pollution method during the whole incubation time. The NRRT in earthworm coelomocytes and micronucleus rate in the multiple-time addition of B[a]P in soil was 5.32-13.00% higher than those in the one-time addition method, respectively. The activities of GST in earthworm and the NRRT in earthworm coelomocytes in the Phe multiple-time superimposed pollution treatment was 3.01%-33.07% lower and 4.72%-26.90% higher than those in the one-time addition treatment, respectively. The very significantly positive correlation (p<0.01) between the amounts of B[a]P and Phe accumulated in earthworms and the GST activities and NRRT in the earthworm were found. These results revealed that GST and NRRT were the better sensitive indicators for assessing the toxicological effects of B[a]P and Phe on earthworm. This results showed that soil available PAHs and its toxicity to earthworms in the multiple-time addition were lower than those in one-time addition one.