Cadmium sorption characteristics of soil amendments and its relationship with the cadmium uptake by hyperaccumulator and normal plants in amended soils

Abstract

In order to select appropriate amendments for cropping hyperaccumulator or normal plants on contaminated soils and establish the relationship between Cd sorption characteristics of soil amendments and their capacity to reduce Cd uptake by plants, batch sorption experiments with 11 different clay minerals and organic materials and a pot experiment with the same amendments were carried out. The pot experiment was conducted with Sedum alfredii and maize (Zea mays) in a co-cropping system. The results showed that the highest sorption amount was by montmorillonite at 40.82 mg/g, while mica was the lowest at only 1.83 mg/g. There was a significant negative correlation between the n value of Freundlich equation and Cd uptake by plants, and between the logarithm of the stability constant K of the Langmuir equation and plant uptake. Humic acids (HAs) and mushroom manure increased Cd uptake by S. alfredii, but not maize, thus they are suitable as soil amendments for the co-cropping S. alfredii and maize. The stability constant K in these cases was 0.14-0.16 L/mg and n values were 1.51-2.19. The alkaline zeolite and mica had the best fixation abilities and significantly decreased Cd uptake by the both plants, with K > or = 1.49 L/mg and n > or = 3.59.

Figure 1

Correlations between Cd concentrations in maize and sorption stability constants generated from Freundlich (n) and Langmuir isotherms (K) for soil amendments (The horizontal lines represent the intervals of the mean Cd concentration of the control without amendment. One ∗ and two ∗∗ indicate significant at probability 95% and 99% for the correlation).

Figure 2

Correlations between the Cd phytoextraction rates by Sedum alfredii and sorption stability constants of soil amendments simulated by the Freundlich (n) and Langmuir (K) isotherm models (The horizontal lines represent the intervals of the mean Cd phytoextraction of the control without amendment. One ∗ and two ∗∗ indicate significant at probability 95% and 99% for the correlation).