Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 135

(b)

(a)

(c)

(d)

1

Relative pore volume

Fig. 9 Breakthrough curves of leachates: (a) tracer such as chloride ion, (b) pesticide only, (c) and
(d) pesticide in formulation

The physicochemical properties of pesticide are also an important factor for
surfactant effects on its mobility, which was confirmed by the leaching behavior of
four herbicides in the presence of Tween 80 (Foy 1992). Nonionic surfactants are
considered to increase water penetration by increased dispersion of soil. However, by
comparing their effects on the penetration depth of water with those on the mobility
of dinitroaniline herbicides, Koren (1972) concluded greater importance of sur-
factant-controlled adsorption-desorption balance than water movement. Singh et al.
(2002a) also demonstrated insignificant effects of 12 commercial adjuvants including
organosilicones on downward water penetration in a soil column. The effect of cati-
onic surfactants has been investigated in column leaching studies of norflurazon (46)
(Singh et al. 2002b; Tan and Singh 1995). Addition of quaternary ammonium Adogen
surfactants to dry flowable formulation of (46) at 1:1 (w/w) ratio slightly reduced
mobility at an early stage of leaching, but the substituted imidazoline Monazalin with
an optimized mixing ratio significantly reduced the leaching.
The effect of a cationic surfactant has been more clearly demonstrated in a col-
umn leaching study of linuron (42) (Sánchez-Camazano et al. 2000a). Amendment
of soil by HDTMA Br at the rates of 2 and 15 ton/ha delayed the peak in BTC at a
flow rate of 60 mL/day from 3-4 PV to 8.5 -> 9.5 PV with much smaller eluted
amounts. Under the same conditions, anionic SDS reduced retention in the column
with the peak in BTC at less than 3 PV due to solubilization of (42) to micelles.
A similar soil amendment with 4 w/w% TDTMA Br markedly increased retention
of methidathion (53), as evidenced by the significant delay of the BTC peak from
3 PV without amendment to nearly 100 PV (Sánchez et al. 2003a). Lichtenstein
et al. (1967a) reported increased mobility of parathion (3) and aldrin (52) in a soil
column when 1% anionic SDS was used for elution. Field lysimeter study of atra-
zine (13) has shown that application with a 10-fold amount of anionic SDBS on a
weight basis causes increases of its mobility in soil and the eluted amount
(Scheunert and Korte 1985). In contrast, the anionic surfactant Sulphonic greatly