Agriculture Reference
In-Depth Information
of heavy metal, the knowledge of the total concentration of a specific element
without considering its speciation was not sufficient, because the mobility and
toxicity of heavy metal in contaminated soil were greatly controlled by its
chemical speciation [7]. Heavy metals distributed among many components of
soil solids and associated with them in different ways. The mobility and
bioavailability of heavy metals in solid samples were generally evaluated by
selective sequential extraction. A large number of selective sequential
extraction methods had been reported, but many of which were modified on
the basis of the five-step sequential extraction technique, developed by Tessier
et al. [8]. By this technique, trace element was classified into five fractions:
exchangeable (
F1
), bound to carbonates (
F2
), bound to Fe-Mn oxides (
F3
),
bound to organic matter (
F4
) and residual (
F5
). The studied area is situated in
the suburb of Shengyang, which is major heavy industrial production base in
the region for several decades. Increased contaminants may pose substantial
threat to the local agriculture, as contaminants may enter and accumulate in
topsoil through many approaches [9,10]. Contamination of agricultural soil
may cause long-term environmental and healthy risk. The presence of trace
toxic heavy metals and pesticides in the farmland soil had imposed a need for
better understanding the processes of soil-trace element interactions, in
particular, the mobility and retention mechanism of trace element in soil [11].
A research about trace toxic elements in agricultural soil in Shenyang suburb,
China could provide valuable and insightful information for other regions in
China. The main objectives of the study were to investigate the contents,
speciation and transportation of heavy metals (Pb, Cd, Cr and As) and
organchlorine pesticides (DDT and BHC) in topsoils (0-20 cm) of two
farmland sites near pollutant sources in northeast China and to evaluate the
risk of the four heavy metals and organchlorine pesticides to soil and
agricultural production. Some conclusions obtained from this work are
significant for understanding the transport and fate mechanism of heavy metals
(Pb, Cd, Cr and As) and organchlorine pesticides in topsoils.
2.
C
OLLECTION AND
P
REPARATION OF
S
OIL
S
AMPLES
Soil samples were collected from two sites in moderately contaminated
farmland in Northeast China. Site A (42
º
04.001'N, 123
º
29.352'E) was about
60 m away from a pile of chromium wastes. Residual materials produced in
industrial production containing chromium with great concentration were
