Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 118

Table 7 (continued)

Light source, filter
Temp, reaction medium
Surfactant or formulation

[DT 50 °]
DT 50 s a No. Pesticide/structure Reference

33 Methidathion Sunlight (Jul-Aug),

borosilicate glass

[1.7 d] Sánchez et al.

(2005)

1.6 d

N

15-38°C, soil thin-layer
(0.9 mm)

S OCH 3

N

CH 3 O
CH 3 O

P S

S

O

TDTMA Br (10 × cmc)

13 Atrazine 1 kW Hg lamp, water [5.5 min] Gong et al. (2001)

5.2 min

Cl

28±2°C, soil thin-layer
(0.2-0.5 mm)

N N

SDBS (20 mg/kg soil)

C 2 H 5 NH N NHCH(CH 3 ) 2

Brij-52, C 16 H 33 (OCH 2 CH 2 ) 2 OH; Brij-72, C 18 H 37 (OCH 2 CH 2 ) 2 OH; r.t., room temperature; NA, not
available; None, without filter.
a Half-life of degradation assuming pseudo-first-order kinetics with (s) or without (o) surfactant or
adjuvant.
b Tween 60, monostearate of nonionic surfactant (d) in Fig. 2.

mote photodegradation, as demonstrated for (26) and haloxyfop (27) (Harrison and
Wax 1985). Hautula (1978) has reported the increase of a quantum yield with
shorter half-lives for sunlight photolysis of (26), parathion (3), and carbaryl (8),
partly due to the red shift of their absorption spectra.
The photodegradation process of (26) in micelles has been studied extensively
by Kwan and Chu (2005). SDS micelles did not affect the photodegradation rate,
whereas the other micelles of HDTMA Br, Tween 80, and Brij 35 accelerated it at
pH 3 by a factor of 2.5-5. The more favorable formation of an excimer followed
by an electron transfer to give the anion radical-like species in the latter micelles
resulted in the regioselective dechlorination ( o / p ~ 2) at pH 3, but no selectivity was
detected at pH 10, possibly because of inhibition of dechlorination at the o -position
by the neighboring CH 2 COO − moiety. Photoinduced dechlorination was also exam-
ined for DDT (1) in three alcohol ethoxylate micelles (Chu 1999). Enhancement in
the micelles was about twofold compared with aqueous photolysis via dechlorina-
tion at the CCl 3 group followed by the aryl moieties. In relation to the compartmen-
talization effect, the photodimerization of coumaphos (7) was investigated in SDS
micelles, and more dimers were formed as the occupation number defined by the
ratio of (7) molecule per micelle increased (Moreno et al. 1995).
The photochemical reactions of urea herbicides in nonionic micelles have been
investigated extensively by using monuron (3-(4-chlorophenyl)-1,1-dimethylurea) as
a model compound. Tanaka et al. (1979, 1981) reported an increased rate of photolysis
for monuron in the micelles of nonionic alkylphenoxy ethoxylates. The solubilization
in micelles eliminated ring hydroxylation but the reductive dechlorination was
enhanced. Demethylation proceeded as a minor pathway, with formation of HCHO