The Fate Of Emerging Phenolic Pollutants In Submerged Soil-plants System

Using plants and their associated microbes to degrade xenobiotics is an efficient way to remove variety organic pollutants, especially the recalcitrant pollutants, in environment. The microsites containing soil-water-plants have been proven to accelerate many biotransformation processes of pollutants. Wetland plants can transport O2 to root surface forming oxic zones to stimulate the activity of aerobic microorganisms, their root exudates supply carbon and other nutrients for microbial growth. With the O2 diffusion into the water, the main feature of submerged soil is the presence of adjacent oxic and anoxic zones. Thus, aerobic and anaerobic transformation of pollutants may take place simultaneously in the oxic-anoxic interface of submerged soil. Using a 14C-tracer, we investigated the fate of TBBPA and 4-NP111 in both submerged soil with and without the growth of wetland plants, to elucidate the environmental behavior in wetland-plants system in laboratory scale. These results should be useful in phytoremediation of contaminated sites. The results are follows:1. The sorption of TBBPA and 4-NP111 on diverse source of humic acids was investigated using a dialysis equilibrium apparatus. We found that these two pollutants can adsorb to various humic acids at different degrees. The small organic acid acetic acid at the concentration 0.5×10-3 M markedly increased the adsorption of 4-NPm and TBBPA to humic acids of diverse source, while this small organic acid had little effect on the sorption of BPA to humic acids.2. The fate of TBBPA in submerged soil-plant system. We investigated the fate and metabolites of 14C-TBBPA in a submerged soil-plants systems. Submerged soil with an anoxic-oxic interface supplied a suitable environment for the degradation of TBBPA and the half-life of TBBPA was 20.8 days, accompanied by mineralization (11.5% of initial TBBPA) and the substantial formation (60.8% of initial TBBPA) of bound residues. Four interconnected pathways were proposed in submerged soil with and without the plants:oxidative skeletal cleavage,O-methylation, type Ⅱ ipso-substitution, and reductive debromination to form twelve metabolites (10 in unplanted soil and 7 in planted soil) and one unknown polar metabolite in plant in soil extracts at the day 66. The presence of the seedlings strongly reduced 14C-TBBPA mineralization and bound-residue formation and stimulated debromination and O-methylation. Both rice and reed plants stimulated the biotransform of TBBPA in the soil, while TBBPA dissipation was strongly enhanced by the reed seedlings with a half-life of 11.4 days and the reed seedlings increased monomethyl TBBPA formation (11.3%). Uptake of TBBPA and its metabolites was obvious in our study and considerable radioactivity was detected in rice (21.3%) and reed (33.1%) seedlings, and the results of 14C image scanner and oxidizer showed the radioactivity mainly on or in the roots of plants.3. The fate of 4-NP111 in submerged soil-rice system. We didn’t detect a rapd degradation of 4-NP111 in submerged soil at concentrations of 2 and 20 mg 4-NP111 per kg soil (dry weight) treatments during 180 days incubation without the growth of rice plants and 85.7 ± 0.9% and 81.9 ± 0.8% of total radioactivity were left in the soil extracts at the end of experiment. Using compartmented rhizobox, the decrease of extractable 4-NP111 at different soil layers (root soil, soils with 0.5 cm and 8 cm distance to the roots) were quantified. The fastest decrease of extractable 4-NP111 was observed in the root compartment which only left 11.2 ± 1.7% and 12.2 ± 0.4% of total radioactivity at the day 110 with a unpolar metabolite in soil extract. With the decreasing O2 content and root exudates in the soil layers of 0.5 and 8 cm distance to the roots, decreasing dissipation of 4-NP111was observed in the soil:The extractable 4-NP111 was 23.3±5.3% and 25.5 ± 12.4% of total radioactivity in the root compartment and the 0.5-cm soil layer, while 60.4 ± 4.8% and 65.8 ± 9.0% was left in the 8-cm soil layer at two concentrations at the end of the experiment. Meanwhile, bound residues of 4-NP111 were increased, accounting for 50.1 ± 9.6% and 49.9± 10.5%; 50.1 ± 9.6% and 39.1 ± 2.5% of the total radioactivity in the root compartment and 0.5-cm soil layer, while only 26.2 ± 2.2% and 25.0 ± 3.9% of the total radioactivity was bound to the soil in the 8-cm soil layer. The radioactivity was distributed in the whole plant at day 10 and accounted for 18.3 ± 5.8% and 29.6 ± 7.0% of the total radioactivity at the end of the experiment, the radioactivity in the plant tissues followed the order root> leaves> sheet> rice seeds.As mentioned above, first, we investgated the fate and metaboilsm of TBBPA in in submerged soil-plant system and demonstracted the positive influence of rhizosphere on TBBPA degradation. Then, we studied the dissipation of 4-NP111 in rice rhizosphere at different soil layers and the appearance of the 14C in edible part uptaking by rice plants. Finally, we studied the effects of the small moleculel acetic acid on adsorption of TBBPA and 4-NP111 to diverse source of huminc acid. Further work includling the analysis of bacterial colony, the biotransformation of pollutants in plants and field experiment.