Influences Of Benzo(a)Pyrene And Phenanthrene Superimposed Pollution On Soil Respiration Intensity And Soil Enzymatic Activity

As the persistent organic pollutants with strong carcinogenic, teratogenic and mutagenic effect, benzo(a)pyrene (BaP) and phenanthrene (PHE) are gradually accumulating in soil and posing a serious threaten to soil environment quality. The BaP and PHE bioavailability and their impacts on soil respiration and soil enzymatic activity were investigated under simulated condition by using the superimposed and one-time addition method. The main results are listed as follows:(1) The available fractions of BaP in soil, which were extracted by 2.0 g soil and 0.2 g Tenax-TA with duration of 6 h, had a good correlation with the amounts of BaP accumulated in earthworms. The amounts of BaP extracted by Tenax-TA from soil can be used to predict bioavailable fractions of BaP in soil.(2) The contents of the extractable and available fractions of BaP and PHE were sharply declined in the first 28d (0-28 d), and then slowly decreased between 28 d and 56 d incubation time in both the superimposed and one-time pollution method. The chemical solvent extractable (dichloromethane and acetone,1:1, v/v) and Tenax-TA extractable BaP from soil in the superimposed pollution tests were 34.50%～57.29% and 19.00%～43.80% lower than that in the one-time pollution method, respectively. The chemical solvent extractable (dichloromethane and acetone,1:1, v/v) and Tenax-TA extractable PHE from 0-20cm soil in the superimposed pollution tests were 22.83%～ 34.93% and 1.53%-11.01% lower than that in the one-time pollution method, respectively.(3) Soil respiration intensity was decreased at first incubation stage, and then gradually recovered in both the BaP and PHE superimposed and one-time pollution method. In BaP superimposed and one-time, soil respiratory inhibition rate was reduced as the available fraction of BaP decreasing in soil, the positive correlation were tested between soil respiratory inhibition rate and available BaP(R2=0.8783, P<0.05). In PHE superimposed and one-time, soil respiratory inhibition rate was reduced as the available fraction of PHE decreased in soil, the positive correlations were tested between soil respiratory inhibition rate and available PHE (R2=0.8464, P<0.05).(4) Soil urease and dehydrogenase activities were inhibited at first incubation period, and then gradually recovered under both the superimposed and one-time pollution method.In the BaP superimposed and one-time pollution tests, the significantly positive correlation relationship between soil available BaP and inhibition rate of soil dehydrogenase activity was testified in the whole incubation period (R2=0.9555, P<0.01). The positive correlation relationship between soil available BaP and inhibition rate of soil urease activity was testified in the whole incubation period (R2=0.8197, P<0.01). In the PHE superimposed and one-time pollution tests, the positive correlation relationship between soil available PHE and inhibition rate of soil dehydrogenase activity was testified in the whole incubation period (R2=0.8789, P<0.05). The positive correlation relationship between soil available PHE and inhibition rate of soil urease activity was testified in the whole incubation period (R2=0.7188, P<0.05)(5) The toxicological effects of BaP and PHE on soil respiration intensity, soil urease and dehydrogenase activities in the superimposed pollution tests were lower than that in the one-time pollution ones. Results from this study can provide critical facts for assessing eco-toxicological effects of BaP and PHE in soil.