Utilization of lignocellulosic substrates for the bioremediation of a soil historically contaminated with DDT

Abstract

Most of the soils corresponding to facilities where DDT was historically stored arecurrently contaminated. With the aim of having an efficient bioremediation alternative for a real specific case, the evaluation of treatments consisting of the addition oflignocellulosic substrates to the contaminated soil was carried out. Initial concentrations of 2.63 mg.kg-1 of o,p-DDT and 3.13 mg.kg-1 p,p-DDT were determined in the soil. First,a mixture of contaminated soil: wheat straw was evaluated in two volumetric proportions,70:30 and 50:50. At 90 days after the beginning of the assay, 0.43 mg.kg-1 of o,p-DDTand 2.62 mg.kg-1 of p,p-DDT were recorded in the 70:30 treatment; and 0.22 mg.kg-1 ofo,p-DDT and 1.52 mg.kg-1 of p,p-DDT in the 50:50 treatment. With these preliminary results, it was decided to make a second evaluation, keeping the control, the 50:50 treatment, and adding two new treatments containing substrates of the Pleurotusostreatus fungus, which is recognized for its ability to degrade xenobiotics. Thesetreatments were: soil-wheat straw-spent mushroom substrate of Pleurotus 50:25:25 (SWS-SMS) and soil-wheat straw-fungal cultivation substrate of Pleurotus 50:25:25 (S-WSFS). The dissipation of DDT was evaluated at 0, 15, 30, 60, 90 and 135 days after the beginning of the assay under controlled conditions. With the results obtained, regressions were adjusted to estimate the DT50 and DT90 values of each treatment. In addition, in the samples of 60, 90 and 135 days, the concentrations of the metabolites p,p-DDE and o,pDDD were recorded.The DT50 and DT90 values of both treatments with Pleurotus ostreatus substrateswere notably lower than thecontrol and S-WS treatment (table 1). Even DT90 values ofboth treatments with Pleurotusostreatus substrates werereached within the studyperiod. The S-WS-FStreatment was able to degrade 90% of the initial amount of both DDT isomers in less than 44 days; while, in the control, 677 days were necessary. For both metabolites, the maximum concentration recorded in the soil was 0.25 mg.kg-1; while, in the different treatments it was 0.12 mg.kg-1. This shows that although their initialconcentrations were low, no intermediates compounds appear to have been generated resulting from the degradation of DDT. The use of Pleurotus ostreatus substrates, eitherthrough the use of residual commercial substrates or the use of the fungal cultivation substrates, is a highly effective and very low-cost alternative for the bioremediation of soils historically contaminated with DDT.