Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 154

The effect of formulation on soil dissipation has been reported for some pesti-
cides. Much faster dissipation of azinphos-methyl (39) in the EC formulation than
the granule (G) was observed in the field (Schulz et al. 1970). Since a similar trend
was reported for the EC and G formulations of chlorpyrifos (65) in muck soil but
with an insignificant difference in sandy soil (Chapman and Chapman 1986), the
observed differences between formulations are likely at least in part to originate
from different methods of application where less a.i. is desorbed from the granule.
Ngim and Crosby (2001) clearly showed through field dissipation of fipronil (75)
that less desorption of (75) from the G formulation than the soluble concentrate is
the dominant reason for its longer persistence in soil. When the wettable granule
formulation of (65) was used in field trials on oranges, a similar dissipation rate to
the EC was reported (Montemurro et al. 2002). Insignificant differences in field
dissipation rate among EC and other formulations were observed for atrazine (13)
(Kahn et al. 1981), temephos (72) (Verma et al. 2004), butachlor (74) (Kulshrestha
1987), and oxyfluorfen (76) (Martínez et al. 2004). Dissipation of phenmedipham
(73) applied to a sugar beet field was slightly reduced when refined fatty acid and
paraffinic oil were used as adjuvants, to a larger extent in the former (Kucharski et
al. 2002). The slower dissipation of EC formulations of several pesticides was also
reported by addition of adjuvants (Kucharski 2003). Reduced volatilization by
addition of adjuvants could account for the slower dissipation of trifluralin (15) as
the EC (Swarcewicz et al. 1998).

IX Effects on Bioconcentration

Effect of adjuvants on bioconcentration of pesticide to the edible part of terrestrial
plants is unlikely because of the insignificant increase of translocation from the
applied sites, as discussed in Sections VII and VIII. White et al. (2007) reported the
slightly increased bioaccumulation of DDE (1,1-dichloro-2,2-bis ( p -chlorophenyl)
ethylene) in the root and stem of a zucchini species but not in the fruit. They also
reported the enhanced bioaccumulation of DDE to some earthworm species in the
presence of Triton X-100, Tween 80, and rhamnolipids. In the case of fish, pesticides
in water are considered to be taken up directly from water by gills or indirectly from
food by the gastrointestinal tract. Because either more solubilization or less
adsorption to solid matter is reported for pesticides in the presence of surfactant at
concentration greater than cmc, the effect of adjuvants including surfactant on
bioconcentration is anticipated. Aqueous humic acids having a solubilizing ability
similar to surfactant are considered to reduce the bioavailability of a chemical, which
would result in less apparent toxicity to fish (EPA 1996; Schrap 1991). The OECD
testing guideline on fish bioconcentration does not recommend the use of solvents
or dispersants, to avoid their toxicity and unexpected effects on bioconcentration, but
some of them such as dimethylformamide, Tween 80, and HCO-40 are permitted at
less than 100 mg/L if unavoidable because of the low water solubility of a test chemi-
cal (OECD 1996). Because most regulations only require the fish bioconcentration