Enzymatic transformation of emerging contaminants in soil
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There has been increasing concern regarding presence of emerging contaminants among various environmental compartments. To date, there exists limited research regarding fate and transformation of these compounds in soil. The objective of this research was to develop enzyme based approach to remediate polluted soils. The transformation of three chemicals, 17β-estradiol (E2), perfluorooctanoic acid (PFOA), and sulfadimethoxine (SDM) were investigated in presence of oxido-reductive enzymes. Experiments were conducted using a Cecil sandy clay loam soil preloaded with single contaminant (E2, SDM, or PFOA) at a time and subjected to enzymatic treatments of laccase, horseradish peroxidase, or lignin peroxidase. We also conducted experiments to test efficiency of laccase in presence of mediators (violuric acid (VA), 1-hydroxybenzotriazole (HBT), and 2,2'-azino-bis3-ethylbenzothiazoline-6-sulphonic acid (ABTS)). For laccase treated soil system, approximately 94% of applied E2 was non-extractable while in HRP treated soil, 97% of applied E2 remained non-extractable. For both enzymes, about 75% applied of 14C labeled E2 was incorporated in soil organic matter (humic acid). In the soil system spiked with SDM, reduction in extractable SDM was 42% with laccase, 46% with HRP and 28% with LiP. Application of laccase with ABTS was found to be most effective treatment in reducing the extractable SDM to 57%. For soil system containing PFOA, with addition of laccase about 40% of applied PFOA was extractable. Addition of mediators along with laccase resulted in enhanced reduction of extractable PFOA which were 97% with HBT, 90% with VA, and 95% with ABTS. Incubation experiments suggested that enzyme mediated transformation of selected chemicals did not follow degradation pathway in soil but were found to form non-extractable soil bound residues. Overall, increasing enzyme concentration and addition of peat enhanced the formation of non-extractable soil bound residues. Among all the three enzymes laccase was shown to be more efficient in mediating E2 however for SDM, horseradish peroxidase proved to be the efficient one. This laccase-mediator system (LMS) was found to be very efficient for mediating PFOA in soil which is not a direct substrate of laccase. The study provides useful information for understanding and assessing the environmental fate of hormones and for developing a novel soil remediation strategy via enzyme-enhanced humification reactions.