Environmental Engineering Reference
In-Depth Information
Table 8
(continued)
a
“a” and “d” in the parentheses mean adsorption and desorption, respectively.
b
oc, organic carbon (%), corrected by a factor of 1/1.724 from organic matter content; CEC, cat-
ion-exchange capacity (meq/100 g soil); NA, not available;
*
, the usage of CaCl
2
solution as an
aqueous phase.
c
cmc, critical micelle concentration; nEO, polyethoxylated chain with a unit number of n.
d
Freundlich sorption coefficient (L/kg) and the constant estimated by batch equilibration tech-
nique; x/m =
K
F
•
C
1/n
, where x and m are the amounts of pesticide and soil and C is the aqueous
concentration of pesticide. If the n column is 'L',
K
F
means the sorption coefficient in linear
isotherm.
e
NP 6EO & Triton N-60, C
9
H
19
C
6
H
4
(OCH
2
CH
2
)
6
OH; NP 18EO, C
9
H
19
C
6
H
4
(OCH
2
CH
2
)
18
OH;
LAS, linear alkylbenzenesulfonate; Triton X-35, C
8
H
17
C
6
H
4
(OCH
2
CH
2
)
3
OH; Triton X-77, mixture
of alkylarylpolyethylene glycols, free fatty acids, and isopropanol; Triton N-150,
C
9
H
19
C
6
H
4
(OCH
2
CH
2
)
15
OH; Span 20, sorbitan monolaurate; Soprophor FLK, phosphate tristyryl-
phenol ethoxylate; MNS90, sodium alkylnaphthalenesulfate.
contents (<1%) but caused slightly less adsorption for soils with higher oc
(Werkheiser and Anderson 1996). In addition to soil characteristics, the ability of
surfactant to disperse soil matrix and then increase the sites for adsorption is also
considered to be an important factor (Tao et al. 2006).
The desorption of pesticide from soils is also affected by surfactant. Both
Triton X-100 and Tween 80 at higher concentrations than cmc could enhance the
desorption of hydrophobic lindane (34) from soil but an insignificant effect was
observed by SDS, which seemed to depend on the hydrophobicity of surfactant
(Quintero et al. 2005). In contrast, the efficiency of desorption of more hydrophilic
aldicarb (60) from soil by Triton X-100 above cmc was less than those of
HDTMA Br and SDS (Xu et al. 2006). Mata-Sandoval et al. (2002) reported
insignificant desorption of pesticides from soil by Triton X-100 below cmc, but
the enhanced desorption above cmc was observed in the order of trifluralin (15)
> coumaphos (7) >> atrazine (13). Similar profiles were obtained for rhamnolipid
biosurfactant. This order is in agreement with that of log P and, therefore, the
above different effects in desorption are likely to originate from the affinity
between pesticide and surfactant. When the Freundlich isotherm is compared
between adsorption of pesticide to and its desorption from soil, the n values are
different because of hysteresis. To quantify the hysteresis, the H value defined by
n (adsorption) / n
d
(desorption) is utilized and usually increases with soil organic
matter content. The greater the desorption efficiency of surfactant at a concentra-
tion higher than cmc, the lesser the H value. These profiles have been confirmed
by the adsorption and desorption studies of atrazine (13) and linuron (42) for
several soils with the desorption efficiency proportional to the surfactant concen-
tration (Sánchez-Camazano et al. 2000a,b). When soil applied with pesticide is
aged, the desorption profiles are known to change compared with those from a
Search WWH ::
Custom Search