Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 114

sis (Singh and Sonar 1985; Singh and Raghuraman 1985, 1986). Both the cage and
preorientational effects by SDS micelles resulted in the regioselective formation of
o -migration products with higher yields than organic solvents.
Pesticides
The effect of adjuvants on photolysis of pesticides has been studied as a deposit or
thin film on a glass surface, in aqueous solution, and on soil surface (Table 7). An
insignificant effect was observed in many cases, but some adjuvants seem to accel-
erate photodegradation of pesticides. On the glass surface, Tween-type surfactants
significantly promoted photodegradation of chinomethionat (21) by UV light, pre-
sumably because of sensitization (Nutahara and Murai 1984). In contrast, these
surfactants showed an insignificant effect on photodegradation of sulfonylurea her-
bicides (Thomas and Harrison 1990). The photostability of azadirachtin-A (25) was
investigated by using nine nonionic surfactants, and some of them were considered
to promote photolysis via energy transfer to the pesticide (Johnson and Dureja
2002). Enhanced photodegradation of silcotrione (24) in formulation was reported
on the film of carnauba wax by using a solar simulator (Halle et al. 2000). A three-
fold-higher rate of intramolecular cyclization of (24) to the corresponding chrom-
one derivative was observed as compared with the a.i.
Hautala (1978) investigated the effect of HDTMA Br and SDS on photolysis of
the methyl ester of parathion (3), carbaryl (8), and 2,4-D (26) on soil thin layers.
The surfactants gave insignificant or inconsistent effects on photodegradation of (3)
and (26), while (8) was found to degrade faster in soils at higher moisture contents,
at least in part from catalytic hydrolysis. Similarly as (3), the addition of TDTMA
Br to methidathion (33) on a soil thin layer did not show any marked change of
degradation under natural sunlight (Sánchez et al. 2005). Because light attenuation
is significant on the soil surface, the movement of pesticide molecules in soil is
considered to control the extent of photodegradation (Katagi 2004). Under natural
sunlight, the degradation rate of atrazine (13) in a soil thin layer was greater in wet
soil than dry (Gong et al. 2001; Xiaozhen et al. 2005). A larger photic depth was
estimated, especially in the presence of SDBS, because of the enhanced movement
of (13) in soil by solubilization. Difference of formulation affected the photodegra-
dation of napropamide ( N , N -diethyl-2-(1-naphthalenyloxy)propanamide) (Stanger
and Vargas 1984). On a glass plate the herbicide in EC formulation was photode-
graded much faster under sunlight than that in a wetted powder (WP), while a
slightly faster degradation in WP formulation was observed on soil.
In contrast to photodegradation on solid surfaces, more investigations have been
conducted in solution. The butyl ester of 2,4-D (26) in hexane was photodegraded
slightly faster than its formulation with formation of the dechlorinated derivative
(Que Hee et al. 1979). Butyl 2-hydroxyphenylacetate in trace amounts was consid-
ered to be formed via photo-Fries rearrangement under the cage effect of micelles,
as the formulation contained about 5 % (w/w) surfactants. When the adjuvants in
formulation contain aryl compounds, their photosensitization is considered to pro-