Agriculture Reference
In-Depth Information
Cd > As > Pb > Cr. Heavy metals in root, stem, leaf and fruit of plants
near the studied sites were also analyzed. The result indicated that the
contents of heavy metals in root were higher than that in stem and leaf
and their contents in fruit were lower. The results of adsorption
experiment showed that the adsorption amounts of heavy metals by the
topsoils were greater than that of organchlorine pesticides, and the
adsorption amounts of Pb
2+
and Cd
2+
were greater than that of anionic Cr
(VI) and As (V). By soil column leaching tests, it could be found that the
transport speed of Cr (VI) and As (V) in the agricultural topsoil was
much greater than that of Pb, Cd and BHC, and the transport speed of Cr
(VI) was greater than that of As (V). For heavy metals, the relative
concentrations of exchangeable fraction with higher bioavailability and
mobility were increased in range of 1.2 %- 5.4 % after leaching tests,
which increased the threat of Pb, Cd, Cr and As to ecological system of
topsoils. Combining the results of adsorption with vertical migration, it
could be founded that among all the pollutants studied, the risks of Cr(VI)
and As(V) were the greatest to groundwater system, and the risks of Pb
and Cd were the greatest to agricultural products. As the usage of
organochlorine pesticides had been prohibited, the limited amount of
residual organochlorine pesticides in topsoils would be adsorbed and
biodegraded gradually, and reduced the risk of organochlorine pesticides
to agricultural products and groundwater system.
1.
I
NTRODUCTION
Heavy metals and pesticides from anthropogenic activities, such as
industrial wastes, mining activity, agricultural production and atmospheric
disposition from burning fossil were commonly discharged into topsoil
environment [1]. Topsoil serves many important functions in our society,
particularly for agriculture production. It is thus of extreme importance to
protect topsoil resource and ensure its sustainability. Environmental hazards
derived from heavy metals and pesticides were close linked to the distribution
and mobility of these elements in soil [2]. The mobility of trace elements in
terms of leachability depended not only on total concentrations of elements in
topsoil but also on the geochemical properties of soil and environmental
factors [3,4]. The transport of trace elements in the topsoil had received
considerable attention [5,6]. Recently, Cr(VI) and metalloid As(V) with high
aqueous solubility brought public health concern since the anionic forms were
considered mobile. Numerous studies were performed to assess the transport
behavior of Cr and As in soil [3,4]. However, to assess environmental impact
