Multiple-time Addition Of Benzo(a)pyrene And Phenanthrene In Soil Influenced On Its Availability And Toxic Effects On Eisenia Fetida

PAHs(Polycyclic aromatic),one of the most persistent organic pollutants(POPs),accumulates in soil and thereby poses a serious threat to soil environment quality.There have been frequent over-estimations of environmental risks of PAHs due to the over-evaluated toxic effects of available fractions with one-time addition method.In this paper,we proposed a new multiple-time addition method aimed at reliable simulation of the process of B[a]P and Phe infiltration into soils.Then,by using multiple-time and one-time addition methods,exposure experiments with different aging times(1,7,14,28,and 56 d)of B[a]P and Phe were conducted to analyze the available B[a]P and Phe contents extracted by Tenax-TA.Earthworms were exposed to soils with different aging time of B[a]P and Phe.After exposure for 7 d,earthworms were collected for analysis of B[a]P and Phe accumulated,enzyme activities of superoxide dismutase(SOD)and peroxidase(POD),malondialdehyde(MDA)contents.The main results are listed as follows:(1)The contents of extractable and available B[a]P(Phe)in soil and its accumulated amounts in earthworms sharply declined in 1~28 d and then slowly decreased in the following 28~56 d of incubation time under both multiple-time and one-time addition methods.As well as the toxic effects of SOD and POD activities and MDA contents on earthworms.(2)The available B[a]P(Phe)contents(extracted by Tenax method)were 37.36%~79.59% and 79.72%~89.76% lower than the extractable contents(extracted by ASE method).In addition,the highly significant positive correlation was noted between accumulated amounts of B[a]P(Phe)in earthworms and Tenax extracted contents of B[a]P(Phe)from soils,the coefficient of associations were 0.927 and 0.935 8(p<0.01).(3)Under B[a]P multiple-time addition,soil available B[a]P contents and accumulated amounts of B[a]P in earthworms were 17.05%~38.60%(p<0.05)and 22.62%~46.81%(p<0.05)lower than those under one-time addition,respectively.The ranges of SOD and POD activities and MDA contents in earthworm coelomocytes under multiple-time addition were respectively 17.34%~50.38%,2.42%~24.48% and 2.78%~16.97% lower than those under one-time addition method during the entire incubation time.Moreover,SOD and POD activities and MDA contents in earthworms were positive correlated with soil available B[a]P contents,the coefficient of associations were 0.695 7(SOD)?0.787 5(POD)and 0.8728(MDA);In addition,SOD and POD activities and MDA contents in earthworms were positively correlated with accumulated amounts of B[a]P in earthworms,with the coefficient of associations 0.680 7(SOD)?0.727 1(POD)and 0.829 0(MDA),respectively.(4)Under Phe multiple-time addition,soil available Phe contents and accumulated amounts of Phe in earthworms were 23.19%~50.15%(p<0.05)and 12.64%~57.89%(p<0.05)lower than those in the one-time addition treatments;The SOD and POD enzyme activities,and MDA contents were 3.40%~47.24%,6.49%~38.02% and 21.30%~57.82% lower than the one-time treatments.The results suggested that soil available B[a]P and Phe contents and its toxicity to earthworms under multiple-time addition were lower than those under one-time addition.Moreover,SOD and POD activities and MDA contents in earthworms were positive correlated with soil available Phe contents,the coefficient of associations were 0.893 4(SOD)?0.870 9(POD)and 0.9305(MDA);In addition,SOD and POD activities and MDA contents in earthworms were positively correlated with accumulated amounts of Phe in earthworms,with the coefficient of associations 0.989 8(SOD)? 0.9571(POD)and 0.9727(MDA),respectively.Results from this study can provide critical facts for assessing eco-toxicological effects of B[a]P and Phe in soil.