Agriculture Reference
In-Depth Information
spectrometry [17]. BHC and DDT were measured by gas chromatography
(GC2010, Japan Shimadzu Company) after solid phase extraction.
Sorption is important for the transport and fate of pollutants. Adsorption
data and adsorption isotherms of heavy metals and organchlorine pesticides on
the two soils are shown in Figure 2. Estimated Langmuir and linear parameters
are listed in Table 3. Regression coefficients (
R
2
) showed that the data of Pb,
Cd and As(V) adsorption followed Langmuir adsorption isotherm and the data
of Cr(VI), BHC and DDT adsorption followed linear isotherm in the
concentration range investigated here.
Table 3. Langmuir parameters for adsorption of Pb,Cd, As(V) and linear
parameters for adsorption of Cr(VI), organochlorine pesticides on soil A
and Soil B
Γ
max
(mg
·
kg
-
1
)
K
d
(L
·
mg
-1
)
K
d
(L
·
mg
-1
)
R
2
R
2
Pollutant
Soil
Pollutant
Soil
16.64×10
-5
A
0.23
12902
0.9776
A
0.9626
Pb
β-BHC
15.61×10
-5
B
0.17
10806
0.9548
B
0.9460
0.89×10
-5
A
0.11
3290
0.9079
A
0.9940
Cd
γ-BHC
0.84×10
-5
B
0.08
4158
0.9916
B
0.9975
1.90×10
-5
A
0.07
688
0.9980
A
0.9145
As(V)
ʴ-BHC
0.61×10
-5
B
0.069
689
0.9980
B
0.9869
4.94×10
-5
A
11.674
0.9300
A
0.9982
o,p'-
DDT
Cr(VI)
3.18×10
-5
B
10.870
0.9122
B
0.9990
1.79×10
-5
4.99×10
-5
A
0.9894
A
0.9999
p,p'-
DDT
ʱ-BHC
0.94×10
-5
4.33×10
-5
B
0.9657
B
0.9995
Note:
K
d
means distribution coefficient in Langmuir and Linear equation.
Γ
max
means maximum adsorption amount in Langmuir equation.
As shown in Figure 2, for the two soils, adsorption amounts of the four
metals decreased in the order of Pb > Cd > As(V) > Cr(VI). Different charge
characteristic led to different adsorption ability between Pb/Cd and
Cr(VI)/As(V). Positively charged Pb/Cd was adsorbed by negative sites on the
soil surface. Anionic Cr(VI)/As(V) could be only adsorbed by goethite,
FeO(OH), aluminum oxides and other soil colloids with positively charged
surface sites [18].
In linear equation, the adsorption ability of pollutant by soil was
commonly expressed by adsorption coefficient
K
d
.
K
d
. is the ratio of
adsorption capacity of pollutant by soil to concentration of pollutant in
