RESEARCHES on BIOACCESSIBILITY OF CADMIUM IN RED-BROWN SOIL AND EFFECT FACTORS OF UPTAKE IN PADDY, EASTERN CHINA

Introduction

The Yangtze River Delta Region is an important planting area of paddy and manifests a large scale of red-brown soil. The compositions and trace elements of rhizosphere, bulk soils and paddy shoots were determined in 144 sites. The results address the Cd uptake of paddy is affected by mineral components, fertilization and physiological function of paddy.

Results and Discussion

The exchangeable fraction of metals in soils denotes the absorbability. Data of the exchangeable Cd from bulk soils revealed the proportions to total Cd were 12%-58%. The exchangeable fraction showed a good correlation with pH, SiO₂, CaO and MgO. The positive correlated coefficients presented between the proportion of exchangeable fraction and pH, SiO₂, which indicated the increasing pH and high clay were in favor of release of cadmium. The negative correlated coefficients existed between the proportion and CaO, MgO, which indicated the exchangeable Cd decreased with the ascending carbonates. The proportions of exchangeable Cd in rhizosphere soils were 16%-65%, a little higher than in bulk soils, but its correlations with other compositions were relatively lower. In addiction to four pronounced factors above, K₂O and TOC also took an effect on the exchangeable fraction, due to the fertilization. The uptake coefficients of paddy shoot to cadmium in rhizosphere soils were from 0.1 to 7.3, showing a complicated behavior of uptake.

Conclusions

The high relationships of factors with uptake coefficients decrease with pH>S>CaO> TOC, but they display negative values. Their increasing concentrations of items take disadvantage of paddy uptake to cadmium. Overall, the paddy uptake to cadmium in rhizosphere soils not only depends on mineral components, but also on the fertilization. And the biological function of paddy makes the uptake behavior much complicated.