Treatment And Utilization Of Lead-smelting Polluted Soils In Henan Province

Lead smelting has led to heavy metal accumulation in some farmland soils in Henan Province, and it also threatened the quality and safety of agricultural products. The main objectives of this study were to explore the influence of lead smelting on the heavy metal content in soil in Henan province and to explore the method of phytoremediation of heavy metal-contaminated soils. The results are as follows,(1) Investigation of heavy metal content of 25 wheat(Triticum aestivum Linn)varieties grown in the vicinity of the lead smelting enterprises showed that, grain concentrations of Cd of all 25 varieties as well as 16 varieties for Pb exceeded the maximum permissible concentrations(MPCs). Mean pollution indexes(MPI)(element concentration of wheat grain/MPC for As, Cd or Pb) of the grains varied 0.562-2.15. Nine varieties had MPI<1.0 and considered least hazardous for consumption. Grain concentrations of As, Pb and Zn correlated with the concentrations of the same element in certain other tissue components positively(p<0.05). As, Pb and Cd concentrations contributed 5.22, 40.0 and 54.8%, respectively, to the MPI for all 25 varieties.(2) A field experiment for screening of low Cd wheat varieties was conducted in lead-smelting polluted soils in Jiyuan with 100 wheat(Triticum aestivum Linn) varieties or strains. The results indicated that, among all 100 varites and strains, Luomai 23, Luohan 6, Xinmai 26, Bainong 3217, 08H277-18-7, Pingan 7, Luohan 8, Huai 05155, Xinong 979, Luomai 24 and Huapei 1 had lower Cd concentrations in the grain, the concentrations ranged 0.147-0.185 mg. kg-1(mean 0.168 mg·kg-1). While varieties and strains Zheng 103, Zhoumai 23, Huayu 198, Huapei 3, Bainong 160, Huapei 8, Xinmai 2111, Zheng 119, Zhoumai 18, Zheng 102, Zhoumai 11 and FY189 had higher concentrations in the grain, the concentrations ranged 0.301-0.383 mg·kg-1(mean 0.327 mg·kg-1). Taking 500 g as the weight of wheat flour consumed by a person with body weight of 60 kg in Jiyuan, if he or she eats Luomai 23 or FY 189, respectively, this person will uptake 22% or 219% more Cd than the recommended values by the WHO.(3) Three lead compounds, which were Pb(NO3)2, Pb SO4 and Pb O(at 20 degrees Celsius, their solubilities in water were 520, 0.0443 and 0.017 g·L-1, respectively.), were added at 0.02 mol·kg-1 into soil, and acetic acid, malic acid or citric acid, were added at 0.005 mol·kg-1 in a calcareous soil and incubated for 100 days. Results showed that the DTPA-Pb concentrations of different treatments ranged between 1100-2800 mg·kg-1, the DTPA-Pb content of soil amended with Pb(NO3)2 only was significantly higher(p<0.05) than those with Pb SO4 or Pb O only. For soils amended with Pb(NO3)2, the DTPA-Pb concentrations ranked Pb(NO3)2 only>Pb(NO3)2+acetic acid> Pb(NO3)2+malic acid> Pb(NO3)2+citric acid. The result suggested that, lead compounds with obvious different solubilies can transform into Pb with relatively high availability in soil, organic acids inhibited the availability of lead in soil, and the more carboxyl radix they have, the stronger the inhibition is.(4) A lead smelting polluted soils in Jiyuan was amended with phosphate only or with Na Cl or combustion residue of honeycomb briquette(CRHB), and Sedum plumbizincicola was then planted to check the effect of different amendments on phytoremediation. The mass yield of the plant ranged 3601-4026 kg·hm-2(dry weigh), shoot uptake of Cd, Pb, Cu and Zn of the plant ranged 168-221, 173-267, 17.4-26.8 and 6498-7855 g·hm-2, respectively. Phosphate amendments resulted in reduction of the DTPA-Cd, Pb and Zn of 2.23, 0.389 and 0.182 mg·kg-1, respectively. Shoot concentrations of Pb decreased 2.48%, while those of Cd and Zn increased 13.4% and 10.6%, respectively. Compared with phosphate only amendment, when the soil was amended with phosphate and high dose of Na Cl, the DTPA-Pb content increased, while that of Cd decreased. The CRHB amendment resulted in 4.31% lower of DTPA-Pb in soil than the control. Shoot of Sedum plumbizincicola uptook 4.11%-5.45% of soil Cd, and 35.8%-43.7% of Zn, while the percentages for Cu and Pb were much lower. The results suggested that phosphate and CRHB helped the immobilization of heavy metals in the polluted soils, while Na Cl had a minor effect of the availability and phytoextraction of heavy metals in soil.