Influence of tea polyphenols amendment to contaminated soil on lead speciation, transformation, and bioavailability

Abstract

To verify whether tea polyphenols (TP) could be used as Pb chelating agents to alleviate the problem of Pb contamination in tea, we conducted a greenhouse study using soil bioavailability extraction, sequential extraction fractionation, and X-ray absorption near-edge structure spectroscopy (XANES) to understand and clarify the effect of TP on Pb speciation transformation and bioavailability changes in the soil. TP and Pb(NO3)2 were amended by root watering and four treatments as flowing: (1) CK, deionized water containing no TP and Pb; (2) TP, 2.6 g kg-1 TP; (3) Pb, 400 mg kg-1 Pb; and (4) PbTP, 400 mg kg-1 Pb and 2.6 g kg-1 TP. The improvability of growth and development and the increase of dry matter accumulation after adding TP to Pb-polluted soil indicated that TP had a striking effect on detoxification of Pb. Pb bioavailability characterized by Pb concentration in tea plants, DTPA, and EDTA extraction showed that TP could increase soil Pb bioavailability under low concentration of Pb, whereas TP inhibited it under the high concentrations of Pb. Sequential extraction fractionation in the soils suggested that the effects of TP on Pb species transformation varied among different treatments and TP could enhance the transformation of detrital form of Pb to other forms. Combining with XANES evidence of Pb, the research suggested that TP played an important role in detoxification of Pb and regulation of Pb speciation transformation and bioavailability in soil and could be used as a Pb chelating agent to alleviate the problem of Pb contamination in tea in the future.