Fundamental study of degradation of dichlorodiphenyltrichloroethane in soil by laccase from white rot fungi

This research describes application of laccase from white-rot fungi [polyporus] to remove dichlorodiphenyltrichloroethane in soil. The degradation kinetics of dichlorodiphenyltrichloroethane in soil was also investigated by laboratory batch experiments. The results showed that laccase from white-rot fungi can effectively degrade dichlorodiphenyltrichloroethane and the degradation of total dichlorodiphenyltrichloroethane [the sum of the four dichlorodiphenyltrichloroethane compounds in a sample] was pseudo-first-order kinetics. The residues of almost all the dichlorodiphenyltrichloroethane components and total dichlorodiphenyltrichloroethane in soils treated with laccase decreased rapidly during first 15 days and then kept at a stable level during next 10 days. The residues of total dichlorodiphenyltrichloroethane in soils with different dosages laccase decreased by about 21-32%, 29-45%, 35-51% and 36-51% after 5, 10, 15 and 25 days of incubation, respectively. The half-life of total dichlorodiphenyltrichloroethane in soils with different dosages laccase ranged from 24.75 to 41.75 days. The residues of total dichlorodiphenyltrichloroethane in three different types of soils decreased by 25-29%, 39-43%, 44-47% and 47-52% after 5, 10, 15 and 25 days of incubation with laccase, respectively. The half-life of total dichlorodiphenyltrichloroethane in different types of soil ranged from 24.71 to 27.68 days. The residues of total dichlorodiphenyltrichloroethane in soils with different pH levels decreased by 18-24%, 29-39%, 36-39% and 39-50% after 5, 10, 15 and 25 days of incubation with laccase, respectively. The half-life of total dichlorodiphenyltrichloroethane ranged from 25.63 to 36.42 days. Laccase can be an efficient and safe agent for remediation of dichlorodiphenyltrichloroethane-contaminated soil

Remediation of soil co-contaminated with pyrene and cadmium by growing maize [Zea mays L.]

Sites co-contaminated with organic and metal pollutants are common and considered to be a more complex problem as the two components often causes a synergistic effect on cytotoxicity. Phytoremediation has been proposed as a cost-effective technology for treating heavy metal or organic contamination and may be suitable for remediation of co-contaminated soil. This study investigated theconcurrent removal of pyrene and cadmium in co-contaminated soil by growing maize in a pot experiment. At the end of 60 day culture, pyrene in spiked soil diminished significantly, accounting for 21-31% of the initial extractable concentration in unplanted soil and 12-27% in planted soil. With the increment of cadmium level, the residual pyrene both in unplanted and planted soil tended to increase. Although the presence of cadmium increased the accumulation of pyrene in maize, plant accumulation only account for less than 0.30% of the total amount of the dissipated pyrene in vegetated soils. It implied that plant-promoted microbial biodegradation was the predominant contribution to the plant-enhanced dissipation of pyrene in co-contaminated soil. Unlike pyrene, heavy metal cadmium cannot be degraded. It was observed that maize can concurrently removed about on the average 0.70% of the total cadmium amount in soil by plant uptake, but Cd phytoextraction would be inhibited under contamination of pyrene. Maize CT38 can normally grow in the co-contaminated soil with high level Cd and pyrene and can effectively remedy the sites co-contaminated with these two types of contamination, which suggest the possibility of simultaneous phytoremediation of two different contaminant types