Evaluation of organic amendment on the effect of cadmium bioavailability in contaminated soils using the DGT technique and traditional methods

Abstract

Organic amendments have been widely proposed as a remediation technology for metal-contaminated soils, but there exist controversial results on their effectiveness. In this study, the effect of pig manure addition on cadmium (Cd) bioavailability in Cd-contaminated soils was systematically evaluated by one dynamic, in situ technique of diffusive gradients in thin films (DGT) and four traditional methods based on the equilibrium theory (soil solution concentration and the three commonly used extractants, i.e., acetic acid (HAc), ethylenediamine tetraacetic acid (EDTA), and calcium chloride (CaCl). Wheat and maize were selected for measurement of plant Cd uptake. The results showed that pig manure addition could promote the growth of two plants, accompanied by increasing biomasses of shoots and roots with increasing doses of pig manure addition. Correspondingly, increasing additions of pig manure reduced plant Cd uptake and accumulation, as indicated by the decreases of Cd concentrations in shoots and roots. The bioavailable concentrations of Cd in Cd-contaminated soils reflected by the DGT technique obviously decreased with increasing doses of pig manure addition, following the same changing trend as plant Cd uptake. Changes in soil solution Cd concentration and extractable Cd by HAc, EDTA, and CaCl in soils were similar to DGT measurement. Meanwhile, the capability of Cd resupply from solid phase to soil solution decreased with increasing additions of pig manure, as reflected by the decreases in the ratio (R) value of C to C. Positive correlations were observed between various bioavailable indicators of Cd in soils and Cd concentrations in the tissues of the two plants. These findings provide stronger evidence that pig manure amendment is effective in reducing Cd mobility and bioavailability in soils and it is an ideal organic material for remediation of Cd-contaminated soils.

The Combination of DGT Technique and Traditional Chemical Methods for Evaluation of Cadmium Bioavailability in Contaminated Soils with Organic Amendment

“…Soil used in this study was collected from a suburb of Nanjing city in Jiangsu Province, China, which has adopted the “inter-planting mode” with paddy rice and wheat. Basic properties of this soil have been previously described [ 5 ]. Collected soil was typically yellow-brown in color, which is observed to be widespread in China.…”

“…Cadmium concentrations in the plant tissues were determined by atomic absorption spectrophotometry (Z-81001, Hitachi Ltd., Hitachi, Japan) following digestion with HNO 3 /HClO 4 . To ensure accuracy, increase precision, and reduce experimental error (<5%), quality control (GBW(E) 081581, Bureau of Standard Measurement, Beijing , China) of the analytical method was conducted every ten samples using a certified standard solution [ 5 ]. After harvest, the remaining soil samples were air-dried at room temperature and then sieved with a 2 mm stainless steel mesh for analysis of various parameters (described below).…”

“…The overuse of Cd-containing pesticides and fertilizers may also increase the concentration of Cd in the soil [ 3 ]. Due to its widespread occurrence, and its bioaccumulating and biomagnifying effect throughout tropic chains, Cd monitoring has become an area of increased research focus [ 4 , 5 ]. Excavation, phytoremediation, leaching, electro remediation, solidification, and stabilization are some of the many engineering and chemical techniques that have been proposed to reduce Cd bioavailability in contaminated soils [ 6 ].…”

“…Using these approaches, Cd is accumulated in plant tissues and removed from the soil through the harvest of these plants [ 8 , 9 ]. However, due to the high selectivity of the biotic for the target elements, the capacity of plants to contain Cd, and the mobility of the element in soil, phytoremediation also does not supply an adequate solution to the reduction of Cd bioavailability in the soil [ 5 ]. Consequently, due to the severe implications of Cd contamination in the soil, the availability of a robust tool for the immobilization of Cd labile fractions is critical.…”

“…Some studies have revealed that the addition of organic materials might increase the ability of soil to bind the target element, making these contaminants available for removal through the remediation processes of sorption, precipitation, or complexation [ 9 , 10 , 11 , 12 ]. Yao et al [ 5 ] have also indicated that typical organic pig manure could significantly reduce Cd toxicity interrestrial plants, such as wheat and maize. Additionally, the addition of organic materials could supply sufficient nutrients to plants and improve water retention in soil.…”