Agriculture Reference
In-Depth Information
disposed for about fifty years. Leachate from the disposal had restrained the
growth of corn plants covering the site. Site B (41
º
38.05'N, 123
º
4.35'E) was
about 30 m away from another river seriously polluted by industrial
wastewater and sewage. The farmland had been irrigated using the wastewater
from the river for a long time and although wastewater irrigation was already
prohibited, heavy metal pollution (especially Cd and Pb) of the agricultural
soil had been serious. Soil were sampled from topsoil layer 0-20 cm. Soils
were thoroughly mixed and air-dried after removing gravel and plant residues.
The soils were crushed using an agate mortar and then passed through a 100
mesh nylon sieve. Some basic physicochemical properties of the soils are
shown in Table 1.
3.
H
EAVY
M
ETALS
(P
B
,
C
D
,
C
R AND
A
S
)
AND
O
RGANCHLORINE
P
ESTICIDES
(DDT
AND
BHC)
IN
O
RIGINAL
T
OPSOILS AND
P
LANTS
Different origin resulted in the content difference of heavy metals in soils
(Table 1). In accordance with the Environmental Quality Standard for Soils
[12], the original two soils were found moderately or heavily contaminated
with one or more of the four elements. it could be found that the content of Cr
in soil A was greater than the first grade of environmental quality standard for
soils, which was due to the presence of landfill of chromium wastes from site
A approximately 60 m. The concentration of Cd in soil B was greater than the
second grade of China soil standards (GB 15618-1995) because of long-term
waste water irrigation in the past several decades. Although waste water
irrigation was already prohibited, heavy metal pollution for majority of soils
was serious, especially for Cd pollution. Site B was affected seriously by
polluted river, therefore the content of heavy metal except Cr was relatively
greater than that of soil A. Collectively, the findings suggested that trace toxic
elements had been accumulated in the soils due to the emissions of pollutants
into the studied area in recent years. Several major isomers of BHC and DDT
were all detected in the two soils. The total content of BHC (ΣBCHs = ʱ-BCH
+ β-BHC + γ-BHC + ʴ-BHC) in the soil B (105.96 μg
·
kg
-1
) was about 6 times
of the soil A (16.47 μg
·
kg
-1
), and exceeded the background values of soil (50
μg
·
kg
-1
) about 1 times. The total content of DDT (ΣDDTs = o, p'-DDT+ p, p'-
DDT+ p, p'-DDE + p, p'-DDD ) of soil A was 3 times higher than that of soil
B, and exceeded the soil background values of 30.97 μg
·
kg
-1
.
