In Situ Immobilization Of Cu By Plant Polyphenols In Contaminated Soils

The environmental behavior and bioavailability of Cu affected by vegetable tanning extract contained plant polyphenol L (PPL) and Y (PPY) were studied. The results showed that PPL and PPY could bind strongly Cu with a higher conditional stability constant. Compared with PPL, PPY exhibited a higher affinity with Cu. The affinity of PPL or PPY with Cu increased with the increase of soil pH. Unlike other organic chelating agents, PPL or PPY can be precipitated when PPY or PPL-Cu complex formed.The Cu sorption by the selected acidic or calcareous soil amended with PPL or PPY was increased greatly. Correspondingly, the dissolution of Cu in the Cu-contaminated soils was reduced in the presence of PPL or PPY. Within the Cu and polyphenol solution concentration range studied, the increase in Cu sorption caused by PPY was consistently greater than PPL. The Cu sorption isotherms could be well described by the Freundlich equation. In the presence of plant polyphenols, Cu sorption capacity by both soils was 3-6 times higher than that of control hi the absence of plant polyphenols. Increasing the polyphenols solution concentration resulted in a significant enhancement of Cu sorption by both soils, especially at the range of 0-400 mgC/L of polyphenols solution. The Cu sorption was increased by 33.3% and 56.6% with a polyphenol solution increment of 100mgC/L for PPL and PPY, respectively, in acidic sandy soil, and correspondingly 14.1% and 21.4% in calcareous soil. In addition, the decrease of Cu dissolution in the contaminated soils with an increase of the concentration of plant polyphenols for both soils could also be observed.The decomposed dynamics of PPL and PPY and 8-hydroxyquinoline and Cu environmental behavior in acidic and calcareous soils were studied by aerobic incubation. The results showed that plant polyphenols decomposed more quickly in two weeks after applied than 8-hydroxyquinoline. The decomposition rate of PPL, PPY and 8-hydroxyquinoline was 65.3%, 37.8% and 27.0%, respectively. In comparison with the check, concentration of water-soluble Cu was decreased significantly, which concentration was 0.248-0.316 times in acidic soil and 0.063-0.276 times in calcareous soil as that of control. So the stability of different treatments were as follows: 8-hydroxyquinoline>PPY >PPL. Cu was released with the decomposition of plant polyphenols. It was found that Cu content had a negative correlation with that of plant polyphenol, especially in calcareoussoil. However, we found that there was no linear correlation between the concentration of soluble Cu and pH.The leaching mechanism of Cu in soils results showed that Cu availability and leaching was decreased when PPL and PPY were added in soils. This effect was not the result of pH decrease. In addition, during the leaching with different concentration of PPL and PPY, the disorption percent of Cu were increased yet lower than control treatment. PPY plays more role than PPL. There is a negative linear correlation between DOC concentration of plant polyphenols and of disorption percent of Cu.Effects of Cu bioavailabilty by plant polyphenols were studied by two pot experiments. Cu contents in wheat were dropped 1.01%-58.5% in acidic soil and 13.8%-33.6% in calcareous soil with plant polyphenols added. It can also be obtained in rice. The stability of different treatments were as follows: 8-hydroxyquinoline > PPY > PPL. Uptake of complexed Cu by rice was studied by hydroponic culture experiment. PPL and PPY could complex with Cu when added into culture solution sot that the Cu content of rice exudates decreased, which was less than that of Cu2+ treatment. Cu concentration of free Cu treatment is 2.14-3.08 tunes of that of polyphenols treatment. The tannin content of different treatments were as follows: control>L-Cu>Y-Cu. There is a highly positive linear correlation between tnnin and Cu content.Therefore, vegetable tannin extracts which contained plant polyphenols are good selection for stabilizing heavy-metal contaminated soils.