Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 142

account for this retardation. A similar mechanism was considered to operate for the
soil metabolism of acetochlor (44) in the presence of SDBS (Ye 2003). In the case
of soil metabolism of linuron (42), SDS was found to enhance its biodegradation
but HDTMA Br showed an insignificant effect (Rodriguez-Cruz et al. 2001). SDBS
enhanced the aerobic biodegradation of aldicarb (60) in soil by 28%-57%, which
was explained by the increased solubility of (60) and the change of soil pH by the
surfactant (Liu et al. 2003).
Enhanced aerobic biodegradation even at a higher concentration where synthetic
surfactant shows an inhibitory effect has been reported for biosurfactants. Surfactin,
a biosurfactant produced by Bacillus sabtilis , has been reported to promote the
aerobic biodegradation of endosulfan (6,7,8,9,10,10-hexachloro-1,5,5 a ,6,9,9 a -
hexahydro-6,9-methano-2,4,3-benzodioxathiepin 3-oxide) by approximately 30%
for both

-isomers without accumulation of the corresponding diols and
sulfates (Awasthi et al. 1999). Mata-Sandoval et al. (2000, 2001) investigated the
effect of rhamnolipid mixtures produced by Pseudomonas aeruginasa UG 2 on the
aerobic degradation of coumaphos (7), atrazine (13), and trifluralin (15) by
Streptomyces PS 1/5 in a liquid medium and soil slurries and showed its effective-
ness even at higher concentrations.
Adjuvants in formulation are known to affect the biodegradation of pesticides.
Soil metabolism of azinphos-methyl (39) in its EC formulation was retarded by a
factor of 3-4 compared with the application of a.i., and much slower degradation
was observed for its granule formulation (Schulz et al. 1970). Microbial degrada-
tion of some pyrethroids in a culture medium was slightly reduced for their formu-
lations (Grant 2001). In contrast, the effect of formulation on the biodegradation of
propetamphos (( RS )-[( E )- O -2-isopropoxycarbonyl-1-methylvinyl O -methyl ethyl-
phosphoramidothioate]) in sediments (García-Ortega et al. 2006) and imidacloprid
(32) (Sarkar et al. 2001) and chlorotoluron (40) (Cotterill 1988) in soil was insig-
nificant. Monkiedje et al. (2003) reported the insignificant effect of adjuvants in the
EC formulation of metalaxyl (45). Bromilow et al. (2003) reported some enhanced
biodegradation of several pesticides in water-sediment systems, possibly resulting
from the increased microbial population, by the aid of coformulants. The bioavail-
ability of pesticide in organoclay formulation prepared by mixing clay with a qua-
ternary ammonium ion has been reported to be lower than that dissolved in a
medium for reasons of inaccessibility of microbes to the intercalated pesticides
(Hermosín et al. 2006; Singh et al. 2003).

α - and β

VII Effects on Behavior in Plants

The application of a pesticide formulation in the field is generally classified into
foliar and soil treatments. The behavior of pesticide in the former treatment has
been investigated extensively, not only experimentally but also theoretically by
many researchers, but fewer investigations are available for the latter. The foliar
uptake is initiated by penetration of pesticide through cuticle and sometimes