| Soil heavy metals contamination is an important factor affecting agricultural products safety in China. The application of livestock manures richer with heavy metals to soils will result in accumulation of heavy metals in the soil, which could affect ecosystem health and environmental safety. Therefore, it is urgent need to understand the transfer and transformation of heavy metal in soil-crops and to develop the effective control techniques for heavy metals-polluted soils. A series of pot experiments were conducted to understand the transfer and transformation pattern of Cu in black soil-wheat (rice) system. The in situ immobilization experiments of Cu using three amendments (coal fly ash, apatite, and bentonite) was performed to evaluate their role and effectiveness of in situ copper immobilization in the polluted soils. The main results obtained were summarized as followings.Conclusions are the followings:(1) Pot experiments were conducted to examine the copper (Cu) fractions, mobility, availability and uptake by rice in black soil affected by application of pig manure (PM). The results indicated that Cu was predominately distributed in organic and residual-bound fractions, while the percentages of carbonate and organic-bound fractions had increased with increasing Cu concentrations in soil. The application of PM at the rate of 1% significantly (p<0.01) reduced the DW-(deionied water) and DTPA-extractable Cu, but the increase in the amounts of TCLP-extractable (toxicity characteristics leaching procedure) Cu was non significant. The application of PM at the rate of 1% significantly reduced the Cu mobility, effectively transformed soil Cu from soluble fractions to stable forms, but application at the rate of 3% exhibited the opposite effect. The uptake of Cu by rice was very low compared with quantities accumulated in soil, however Cu concentrations in grains approached threshold level (GB 15199-94, Cu<10 mg-kg-1) after Cu application of≥400 mg·kg-1 in soil. The application of PM at the rate of 1% significantly (p<0.01) reduced Cu concentrations in rice plant tissues. The results also suggested that manure application with moderate Cu enrichment can decline Cu bioavailability in Cu contaminated soil but long-term and excessive amount of PM has a phototoxic effect and presented a potential threat to human health. Therefore, much attention should be paid regarding application of manures with high amount Cu for environmental and food safety.(2) Total 32 samples of pig manure were collected from scale pig farms in Eastern China. The total concentrations of heavy metals (Cr, Ni, Cu, Zn, Cd, and Pb) in pig manure were determined using an inductively coupled plasma-mass spectrometry (ICP-MS). The leachability and chemical fractions of heavy metals were evaluated by water extraction, toxicity characteristics leaching produce (TCLP) and sequential extraction procedure. The mean concentrations of Cr, Ni, Cu, Zn, Cd and Pb were 31.33,7.24,265.69,752.73,0.49, and 6.46 mg-kg-1, respectively. The total and leachable level of heavy metals showed that Cu and Zn were the predominant pollution elements in the pig manure. Cu and Zn in pig manure were highly correlated, suggesting that they might share a common origin. The mean TCLP leachability of heavy metals in pig manure followed the order of Cu (14.6%)> Ni (11.7%)> Zn (6.5%)≈Cd (6.4%)> Pb (0.9%)≈Cr (0.7%). The sequential extraction results showed that Cu was mainly associated with residual (60.7%) and organic-bound (20.9%) forms, while Zn was mainly associated with residual (44.9%) and Fe-Mn oxide-bound (39.6%) forms. The percentage of heavy metals bound with non-residual fractions (exchangeable, carbonate, Fe-Mn oxide and organic-bound) accounted for 29.0% for Cr,41.4% for Ni,39.3% for Cu,55.1% for Zn,66.4% for Cd and 18.9% for Pb, respectively.(3) Three amendments (coal fly ash, apatite, and bentonite) were applied to the two levels (200 and 400 mg·kg-1) of Cu-treated soil (Udic Agriboroll) at the rate of 1.5% and 2.5%. The effect of amendment application on the bioaccessibility and leachability of Cu in the soil was evaluated using the wheat uptake and single and sequential extraction tests. Compared to non-amended soil treated with 400 mg-kg-1 Cu, the addition of coal fly ash, apatite, and bentonite at the rate of 2.5% increased wheat biomass by 50.5%,41.1%, and 61.7%, respectively. The application of soil amendments did not significantly change the total Cu content, however, amendments significantly (p<0.01) reduced the DW-(deionied water), TCLP-(toxicity characteristics leaching procedure), and DTPA-extractable Cu contents in the soil. Sequential extraction results showed that amendments significantly reduced the water-soluble/exchangeable, carbonate, Fe-Mn oxide and organic-bound fraction contents of Cu but increased the amounts of Cu residual form in soil, indicating that the amendments were effective in transforming soil Cu from non-residual fractions to the residual fraction. The possible mechanisms for Cu immobilization was mainly through chemsorption of Cu associated with amendments and precipitation of insoluble Cu-like minerals. Our results demonstrated that these amendments were effective in reducing the bioaccessibility and leachability of Cu in soil. |
PDF Full Text Request