Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 136

reduced downward movement of atrazine (13) (Abu-Zreig et al. 2000). Radioactive
residues in leachates decreased from 75%-78% to 13%-52% of the applied 14 C by
addition of Sulphonic, but nonionic Rexol and Rexonic slightly increased the 14 C
residues to 80%-87%.
When a pesticide formulation is used for a column leaching study, it seems dif-
ficult to predict pesticide leachability. Addition of emulsifier consisting of nonionic
and anionic surfactants (5:1, w/w) to granules of triallate (54) slightly increased its
movement (Beestman and Deming 1976). Differences in pesticide movement
between formulations have been examined for atrazine (13), imidacloprid (32), and
metolachlor (55), and higher movement in WP and EC was observed ( Bowman
1993; Gupta et al. 2002). Based on accumulated evidence, the combination of pes-
ticide and the type and concentration of surfactant make leaching behavior very
complex.
To avoid the undesirable contamination of groundwater, organoclay formulations
improving the mobility of pesticides have been developed. El-Nahhal et al. (1998)
prepared the organoclay formulation of alachlor (53) by using montmorillonite con-
taining HDTMA + and benzyltrimethyl-ammonium (BTMA + ) ions equivalent to the
clay CEC. Although the HDTMA + -organoclay slightly reduced leaching of (53) in
laboratory columns where the commercial EC formulation caused its leakage from
the 25-cm column, the usage of BTMA + resulted in a maximum leaching depth of
10 cm. The latter organoclay formulation demonstrated, in the field leaching study,
limited movement of (53) to depth of 7cm, whereas distribution at 12-15cm was
observed for the EC. A similar reduced mobility in an organoclay formulation com-
pared with a commercial EC has been reported for metolachlor (55) by using 50%
CEC equivalent PTMA + , but the effect with HDTMA + was minimal (Singh 2006).
Celis et al. (2002) demonstrated the usefulness of HDTMA + -modified montmorilo-
nite to reduce the leaching of hexazinone (59). In contrast to no retention of (59), the
peak in BTC for its HDTMA + -clay formulation was observed at 2.5 PV, correspond-
ing to a delay of 4 d with less elution. A similar effect of HDTMA + was reported for
2,4-D (26), and the longer mixing period to incorporate (26) to the organoclay with a
larger volume of an organic solvent was found to be important in reducing leaching
of (26) (Hermosín et al. 2006). The very low retention of rimsulfuron (29), together
with its metabolites, in a soil column has been reported for its commercial formula-
tion (Martins and Mermoud 1999). ODTMA + -modified organoclay formulations
have been developed for sulfosulfuron (12) and sulfentrazone (56) and succeeded in
reducing their downward movement more than the commercial ones (Mishael et al.
2003; Polubesova et al. 2003).
C Biodegradation
Both enhancement and inhibition of microbial degradation of organic chemicals by
synthetic surfactants and biosurfactants have been reported (Makkar and Rockne 2003;
Miller 1995; Rouse et al. 1994). More bioavailability of a chemical via emulsification,