Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 97

Not only the presence of adjuvant in formulation but also the application method
was found to determine the volatilization rate and amount of DDT (1), 2,4-D (26)
and dieldrin (62) from a Petri dish (Que Hee and Sutherland 1975). The thin film
of the a.i. showed almost complete volatilization at very slow rates, while the
corresponding formulations gave smaller amounts of loss at higher rates. Da Silva et al.
(2001) reported the reduced volatilization of triadimefon ( ( RS )-1-(4-chlorophe-
noxy)-3,3-dimethyl-1-(1 H -1,2,4-triazol-1-yl)butan-2-one) from a glass surface as a
wettable powder formulation but with a decreased rate. Volatilization is considered
to be highly dependent on the vapor pressure of pesticide but the coevaporation
with water may play a significant role, as observed. The isopropylamine salt of
glyphosate ( N -(phosphonomethyl)glycine) was resistant to volatilization from glass
slides under moderate wind speed (Leung 1994). The coexistence of long alkyl
chain fatty acids was reported to significantly reduce volatilization loss of the
fungicide pyrimethanil ( N -(4,6-dimethylpyrimidin-2-yl)aniline), possibly by salt
formation (Green et al. 1998).
Different from a glass surface, volatilization of pesticide from a soil surface
would be a more complex process because soil is heterogeneous and adsorbs the
pesticide. Chapman and Chapman (1986) have demonstrated the importance of
volatilization loss for chlorpyrifos (65) applied as EC formulation to sand by com-
paring its dissipation between closed and open containers. Under controlled air
flow, volatilization rates of thiocarbamate herbicides from six soils were found to
be inversely proportional to their adsorption constants to soils with the insignificant
effect of EC formulation (Ekler 1988). The effect of adjuvant in EC formulation on
volatilization from soil was not consistent among replicates for alachlor (53)
(Dailey 2004). In a wind tunnel study using five pesticides in EC or SC formula-
tions, volatilization amounts from silty sand soil seemed to be positively correlated
with vapor pressure, and a similar trend was observed for their volatilization from
French bean leaves (Rüdel 1997). Either matrix effect or enhanced penetration by
adjuvants is known to reduce volatilization loss of pesticide from plant foliage.
Abietic acid and its esters as a matrix material was found to significantly improve
the volatilization loss of chlorpyrifos (65) from marigold plants, but neither noni-
onic nor anionic surfactants showed an effect on volatilization (Chen et al. 1994).
By analyzing the dissipation profiles in dislodgeable and penetrated residues of
azadirachtin (25) in spruce seedlings, Sundaram (1997) speculated that the addi-
tives in EC formulation enhanced penetration of the pesticide by dissolving epicu-
ticular waxes and reducing the volatilization.

IV Effects on Hydrolysis

One of the most important degradation processes of a pesticide in water is abiotic
hydrolysis (Katagi 2002), and the effect of surfactant on its hydrolytic profiles requires
investigation also from the aspect of preparing practically stable formulations.