Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 139

diffusion relaxation time and the relaxation time for the micelle formation/break-
down. The third process was assumed to be proportional to the gradient of the
chemical concentration across the cell. The factor “f,” a bioavailable fraction of the
micellized chemical, was then expressed as a function of the concentration of micel-
lized surfactant. By analyzing the change of biomass and production of carbon
dioxide as a function of a surfactant concentration and time, they have succeeded in
reproducing the bioavailability of the micellized phenanthrene experimentally
observed. The f values of Trirton X-100 and Brij 30 decrease from 0.8 with an
increase of the surfactant concentration finally to zero, but that of Brij 35 was kept
close to zero at all concentrations tested. The insignificant bioavailability from the
Brij 35 micelles may originate from hydrophilicity of its long polyethoxy chain not
well interacting with hydrophobic cell surface. Brown (2007) introduced the detailed
process of a hemimicellar formation on the cell surface and clarified that the sur-
factant-dependent mass transfer of a hydrophoboic chemical into a cell originates
from the variation of the surfactant sorption on the cell surface. The unavailability of
the intercalated PAHs in HDTMA + - and TDTMA + -modified clays to microbes
showed the importance of the release of a chemical from the partitioned medium
consisting of surfactants (Crocker et al. 1995, Theng et al. 2001).
Pesticides
The effects of adjuvants in formulation on the biodegradation of pesticide in soil or
sediment under aerobic and anaerobic conditions are summarized in Table 10. The
dominant controlling factors on the effects are the type of surfactant and its concen-
tration, but the complex composition in pesticide formulation usually makes it very
difficult to predict the effect of adjuvants on the biodegradation of pesticide.
Amonette and O'Connor (1990) have shown the slower initial degradation of
2,4-D (26) in soils treated with alkylphenoxy ethoxylate having a lower HLB value,
which was accounted for by less bioavailability of (26) due to more solubilization
to micelles. The anaerobic biodegradation of DDT (1) by anaerobes was enhanced
by addition of approximately 10-fold amounts of Brij-35 or Triton X-114, with the
initial reaction rate increasing by a factor of 1.5-3 (You et al. 1996). The main deg-
radate was DDD via reductive dechlorination of (1), and the presence of the sur-
factants did not affect the ratio of non-DDD products. Walters and Aitken (2001)
reported increased anaerobic biodegradation of (1) in soil slurries by addition of
Brij 30 in concomitant with the increased solubilization of (1). Insignificant
enhancement by Tween 80 at the concentrations of 5-to 20 fold cmc was found for
the anaerobic degradation of lindane (34), but its b - and d -isomers were biode-
graded slightly more by addition of the surfactant at 20-fold cmc (Quintero et al.
2005). In contrast, Triton X-100 at the concentration of 5-fold cmc remarkably
inhibited its biodegradation. The addition of nonionic micellar surfactant increased
the amount of mineralization in the soil metabolism of triticonazole (48) formula-
tion, while the higher concentration of alkylnaphthalene sulfate surfactant caused
an inhibitory effect (Beigel et al. 1999; Charnay et al. 2000).