Effect of Natural Acid Peat Application on the Phytoextraction of Cadmium from Contaminated Soils

Abstract

Cadmium (Cd) poses a major environmental and human health threat because of its constant release to the environment through anthropogenic activities. Therefore, cost-effective remediation procedures for Cd contamination should be developed to restore ecosystem heath. Phytoremediation, the use of plants to extract contaminants from soils and groundwater has revealed great potential. However, it is limited by the fact that plants need time, nutrient supply and, moreover, have a limited metal uptake capacity. To increase Cd uptake by plants, the effects of the application of natural acid peat and the resulting decrease in soil pH on the amount of Cd taken up by plants were investigated in a pot experiment using two paddy soils contaminated artificially with Cd. An experiment was conducted using a root-bag technique, and four treatments of peat were applied: control(no peat treatment) and peat application (2.5, 5.0, 10.0 g·kg−1). The peat was applied to the soil at two Cd dosages(2.5 and 5.0 mg Cd·kg−1 soil). The uptake of Cd by plant Brassica campestris ssp. Chinesis L was determined and its relation to the amounts of total and bioavailable Cd in the soil was investigated. It was found that the amount of bioavailabile Cd of the soils, as determined by diethylenetriaminepentaacetic acid (DTPA) extraction, was little affected by applications of the peat, but plant uptake of Cd was enhanced, in some cases up to 114.6%∼123.6%. At the contamination level of 2.5 mg Cd·kg−1 soil, the peat added at a rate of 5.0 g·kg−1 soil increased the Cd concentration in the shoot from 9.7 to 11.6 mg·kg−1 in the blue clayed paddy soil and from 13.1 to 16.1 mg·kg−1 in the yellow mettled paddy soil. At the contamination level of 5.0 mg Cd·kg−1 soil, the peat added at a rate of 10.0 g·kg−1 soil increased the Cd concentration in the shoot from 25.3 to 29.8 mg·kg−1 and from 29.1 to 33.4 mg·kg−1 in the blue clayed paddy soil and the yellow mettled paddy soil, respectively. The amount of Cd in shoots (mg·plant−1) was also significantly increased by the application of 5.0 and 10.0 g peat·kg−1 soil. The enhancement is attributable to the decrease in pH and chelate-assisted phytoextraction, resulting in higher Cd availability.