Surfactant Effects on Environmental Behavior of Pesticides - Reviews of Environmental Contamination and Toxicology - page 70

been developed by considering the physicochemical properties of the pesticide, not
only to maximize their efficacy but also to prevent unfavorable environmental con-
tamination from pesticide and its degradation products. A lower water solubility of
the pesticide usually leads to utilization of a water-miscible organic solvent and
formulation additives (adjuvants) including surface-active agents (surfactants) to
solubilize, suspend, or disperse the active ingredient (a.i.) of pesticide in its aque-
ous solution being applied in agricultural practices. Among adjuvants, surfactants
are some of the most important components and can improve the biological activity
by modifying spray droplet size, retention, and spreading on leaf surfaces or by
enhancing uptake and translocation of the a.i. to crop (Knowles 2001). The various
kinds of surfactants with a wide variety of molecular weight and ionic character as
well as natural and petroleum oils are used as wetting, spreading, sticking, and
penetration agents and humectants (Hazen 2000; Krogh et al. 2003).
The main types of pesticide formulation containing surfactant are listed in
Table 1. The surfactant in these formulations generally occupies less than 10%
(w/w), and the remaining consists of various additives such as oils, polymers, and
carriers. The emulsifiable concentrate (EC) using petroleum-based solvents and
dust (D) made of inorganic carriers are typical formulations that have been used,
but now they are being replaced by more environmentally benign formulations to
avoid unfavorable ecotoxicity and contamination by spray drift.
When a pesticide formulation is applied in the field, the adjuvants including
surfactants are distributed via many routes in the environment, depending on their
physicochemical properties (Fig. 1). Surfactants also undergo abiotic degradation
such as hydrolysis and sunlight photolysis together with metabolic transformation

Table 1 Principal types of pesticide formulation containing surfactants in their typical
composition
Formulation type A.I. % Surfactant % Other components (%)

Granules (G) 1-40 0-5 Stabilizer (1-2), polymer or resin (0-10),

Binder (0-5), carrier (to 100)

Wettable powder (WP) 10-80 1-2 Dispersing agent (2-5), antifoaming

agent (0.1-1)
Inert filler/carrier (to 100)

Soluble concentrate (SL) 20-70 5-15 Antifreeze agent (5-10), water-miscible

solvent (to 100)

Emulsifiable concentrate (EC) 20-70 5-10 Solvent/co-solvent (to 100)

Suspension concentrate (SC) 20-70 2-5 Propylene glycol antifreeze (5-10),

antisettling
Agent (0.2-2), water (to 100)

Water-dispersible granules
(WDG)

50-90 1-3 Dispersing agent (3-15), disintegrating

agent (0-15)
Soluble or insoluble filler (to 100)

Oil-in-water emulsion (EW) 5-30 < 5% Stabilizer, thickener

Source: From Knowles (2001) and Copping (2000).