Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 147

highest efficacy of the pesticide, and thus the information on side-by-side compari-
son of the residue profiles is generally very limited, not only between the a.i. and
its formulation but also among different formulations. By surveying the accumu-
lated evidence on residue trials of some pesticides, the effects of adjuvants and sur-
factants are summarized in Table 11.
The method of pesticide application, its interception by plants, and weather
conditions are known to be the dominant factors controlling foliar pesticide resi-
dues, and the type of formulation has been demonstrated to be mostly a minor fac-
tor in the dissipation half-life (DT 50 ) of pesticide (Willis and McDowell 1987). The
DT 50 values for organochlorine (Harrison et al. 1967; Mukherjee and Gopal 1999)
and organophosphorus pesticides (Günther 1969; Miller et al. 1969; Montemurro et al.
2002; Pree et al. 1976) decreased in the order of emulsifiable concentrate (EC) >
wettable powder (WP) > dust (D) and WP > EC > D, but their differences were less
than a few days and considered not decisive. In some cases, the effect of formula-
tion has been clearly shown. The WP formulation of vinclozolin (17) was consid-
ered to reduce volatilization loss from the leaf surface of garden pea (Szeto et al.
1989). The addition of Ortho HDD alkylphenoxy ethoxylate to the WP formulation
markedly increased the initial penetration of dimethoate (67) in citrus leaves, but
with no effect on translocation from peel to pulp and the dissipation rate (Woodham
et al. 1974).
Depending on the formulation type and adjuvants, the amount of an initial
deposit and a dislodgeable fraction on crops are known to significantly differ
(Asano et al. 1984; Günther 1969; Holloway and Western 2003). Among the same
formulation types, the composition of adjuvants affected the DT 50 value as well as
the initial residues (Chang-Yen et al. 1983). Sundaram (1986) reported that the
volatility of an adjuvant in relation to droplet size of an applied formulation con-
trols both the initial deposits and dislodgeable residues of fenitrothion (5) on coni-
fer trees and that the presence of non- or low-volatile adjuvant tends to increase the
DT 50 value of residues. Kucharski (2003) reported the longer persistency of several
herbicides in leaves and root of sugar beet when the corresponding EC formulations
were prepared by addition of different emulsifiers. Marshall and Pree (1993) found
different shapes of deposits on apple leaves between EC and WP formulations of
propargite (71) by scanning electron micrography. The greater distribution in the
EC formulation showed higher efficacy, but insignificant differences in either the
initial deposit or DT 50 were observed. The “sticker” adjuvant was shown to increase
the initial deposits of pyrethroid insecticides on soybean and cotton but did not sig-
nificantly alter their persistence and rainfastness (Reeves 1993). Similar effects
were reported for the spreader-sticker adjuvant Bivert in the field application of
chlorothalonil (63) and chlorpyrifos (65) to a cranberry bog (Putnam et al. 2003).
Higher dislodgeable residues of deltamethrin (69) in staked cucumber were
detected by using the concentrate suspension formulation rather than the EC
(Franco et al. 2005). Additives in formulations were shown to enhance the photo-
degradation of azadirachtin (25) by a factor of 5 (Caboni et al. 2002). Cao et al.
(2005) developed a unique suspo-emulsion formulation including anatase TiO 2 as a
photocatalyst to reduce pesticide persistence.