[Environmental effects of applying heavy metal-containing municipal sewage sludge on wheat-rice rotation system on different types of soil].

A pot experiment with the yellow soil and limestone soil from Guizhou province, and paddy soil from Zhejiang Province was conducted to study the impacts of applying municipal sewage sludge containing different concentrations of heavy metals on the wheat and rice growth and their Zn and Cd absorption. The risks of the crop heavy metals pollution caused by the application of the same sludge differed with tested soils. On the yellow soil and paddy soil, applying the sludge containing high concentration heavy metals induced higher pollution risks to the crops. Applying the sludge 1.6% in dry mass and containing 1789 mg x kg(-1) of Zn and 8.47 mg x kg(-1) of Cd to yellow soil made the Zn and Cd concentrations in wheat grains reached 109 and 0.08 mg x kg(-1), and after the second time application of the same dosage of this sludge after rice planting, the Zn and Cd concentrations in brown rice reached 52.0 and 0.54 mg x kg(-1), respectively. However, applying the sludge to calcareous soil had no pollution risk to the edible parts of wheat and rice. Soil NH4OAc-extractable Zn was the main factor affecting the Zn concentration in wheat grain and brown rice, but soil NH4OAc-extractable Cd had less effect on the Cd concentration in wheat grain and brown nce. Applying the sludge containing high concentration Zn and Cd to the three soils made the concentrations of total Zn and Cd in the soils increased significantly, and after the first time and the second time of the application, the total Zn concentration in the soils all exceeded the 2nd level of the national soil environmental quality standards.