Agriculture Reference
In-Depth Information
Pb
C
d
Cr
As
100
80
Exchangeable
Carbonates
Oxides/hydroxides
Organic matter
Residual
60
40
20
0
Soil A Soil B
Soil A Soil B
Soil A Soil B
Soil A Soil B
Figure 1. The percentage of Pb, Cd, Cr and As in different fractions in Soil A and Soil
B.
The method of selective sequential extraction could provide valuable
information of element portioning in soils, sludge, and sediments and also
provided an estimation of their mobility [13]. In this study, the selective
sequential extraction technique of Tessier et al. [8] was used to analyze the
chemical fractions of Pb, Cd, Cr and As in soils before and after tests (double
samples). A minor modification of the selective sequential extraction was used
for determination of exchangeable Cr and As in soils [14]. The chemical
fractions of Pb, Cd, Cr and As in the original topsoil are shown in Figure 1.
Figure 1 showed that Pb and As were associated dominantly with the residual
fractions, followed by the organic fractions. In general, the exchangeable and
carbonate-bound Pb and As accounted <7% of the total Pb and As,
respectively. A significant fraction of Cr in the soils was bound in the residual
phase, and other four fractions accounted <3% of the total Cr. Some studies
showed that Cr was mostly presented in residual fraction of soil at the horizon
or profile scale [15] and widely considered to have a very low geochemical
mobility [16]. Cd in the two soils was mainly associated with the organic
fraction, secondarily with the Fe-Mn oxides fraction, followed by residual
fraction and carbonate fraction. The percent of exchangeable Cd in the soils
was very low.
The contents of heavy metals in corn and bulrush in the vicinity of
sampling site A are shown in Table 2. On the whole, the contents of heavy
metals in the plants of corn and bulrush followed the order of root > stem >
leaf. The content of each metal in corn fruit were much lower than that in corn
plant. This showed that in the migrate process of heavy metals from root to
stem, to leaf, and to fruit. Their concentrations were diluted and diffused. The
content of Cr in corn fruit was obviously greater than other metals, which was
