Enzymatic activities in constructed wetlands and di-n-butyl phthalate (DBP) biodegradation

The bioaccumulation of phthalate acid esters (PAEs) from industrial products and their mutagenic action has been suggested to be a potential threat to human health. The effects of the most frequently identified PAE, Di-n-butyl phthalate (DBP), and its biodegradation, were examined by comparison of two small scale plots (SSP) of integrated vertical-flow constructed wetlands. The influent DBP concentration was 9.84 mg l⁻¹ in the treatment plot and the control plot received no DBP. Soil enzymatic activities of dehydrogenase, catalase, protease, phosphatase, urease, cellulase, β-glucosidase, were measured in the two SSP after DBP application for 1 month and 2 months, and 1 month after the final application. Both treatment and control had significantly higher enzyme activity in the surface soil than in the subsurface soil (P<0.001) and greater enzyme activity in the down-flow chamber than in the up-flow chamber (P<0.05). In the constructed wetlands, DBP enhanced the activities of dehydrogenase, catalase, protease, phosphatase and inhibited the activities of urease, cellulase and β-glucosidase. However, urease, cellulase, β-glucosidase activities were restored 1 month following the final DBP addition. Degradation of DBP was greater in the surface soil and was reduced in sterile soil, indicating that this process may be mediated by aerobic microorgansims. DBP degradation fitted a first-order model, and the kinetic equation showed that the rate constant was 0.50 and 0.17 d⁻¹, the half-life was 1.39 and 4.02 d, and the r² was 0.99 and 0.98, in surface and subsurface soil, respectively. These results indicate that constructed wetlands are able to biodegrade organic PAEs such as DBP.