10
Drift
10.1 Introduction
Pesticide residues and other contaminants can move downwind of target
application sites and undergo transport to nearby as well as distant places.
This opens pathways for exposure to nontarget organisms including people (Kurtz, 1990). Airborne contaminants can be transformed in the air by
a number of processes including oxidation and photochemical reactions; in
some cases, the reactions yield products that are more toxic than the parent
(Seiber et al., 1980). When the transformation product is more toxic than the
parent, it is termed or called “activation.” If the products are less toxic than
the parent, it is termed “deactivation.” Figure 10.1 illustrates the processes
involved in pesticide drift.
Transect studies are useful to follow the movement and distribution of
pesticides and other contaminants in the environment. These residues are
carried by air and distributed downwind where they are deposited to other
more remote environmental compartments such as soil, water, plant surfaces, and biota (Aston and Seiber, 1996, 1997; Ross et al., 1990; Seiber et al.,
1989; Woodrow et al., 1990). Transect studies can also be used as a technique
to locate the source of a contaminant as well as its path. An example is for
chlorofuorocarbons (CFCs), where transect studies identifed urban areas
and transportation corridors as likely sources (Frank et al., 1996).
“Flux studies” measure the amount of pesticides emitted to air, which
occurs during spraying, and due to evaporation and erosion post application.
Near source fux studies conducted shortly after pesticide application provide
emission rates that can be used as source terms for modeling drift to nontarget sites. To comply with the California Toxic Air Contaminant Act, these
“fux studies” have been conducted by or contracted out by the California
Air Resources Board and Department of Pesticide Regulation for pesticides
used throughout the state. Such fux and drift studies have been conducted
for methyl bromide, emitted to the air after fumigation (see Chapter 8 for a
detailed example for methyl bromide applied to soil); parathion and chlorpyrifos, emitted from treated orchards; and toxaphene use in cotton felds
(see Chapter 3) (Seiber and Woodrow, 1981; Woodrow et al., 1983, 1997, 2001).
DOI: 10.1201/9781003217602-10
177
Drift
10.1 Introduction
Pesticide residues and other contaminants can move downwind of target
application sites and undergo transport to nearby as well as distant places.
This opens pathways for exposure to nontarget organisms including people (Kurtz, 1990). Airborne contaminants can be transformed in the air by
a number of processes including oxidation and photochemical reactions; in
some cases, the reactions yield products that are more toxic than the parent
(Seiber et al., 1980). When the transformation product is more toxic than the
parent, it is termed or called “activation.” If the products are less toxic than
the parent, it is termed “deactivation.” Figure 10.1 illustrates the processes
involved in pesticide drift.
Transect studies are useful to follow the movement and distribution of
pesticides and other contaminants in the environment. These residues are
carried by air and distributed downwind where they are deposited to other
more remote environmental compartments such as soil, water, plant surfaces, and biota (Aston and Seiber, 1996, 1997; Ross et al., 1990; Seiber et al.,
1989; Woodrow et al., 1990). Transect studies can also be used as a technique
to locate the source of a contaminant as well as its path. An example is for
chlorofuorocarbons (CFCs), where transect studies identifed urban areas
and transportation corridors as likely sources (Frank et al., 1996).
“Flux studies” measure the amount of pesticides emitted to air, which
occurs during spraying, and due to evaporation and erosion post application.
Near source fux studies conducted shortly after pesticide application provide
emission rates that can be used as source terms for modeling drift to nontarget sites. To comply with the California Toxic Air Contaminant Act, these
“fux studies” have been conducted by or contracted out by the California
Air Resources Board and Department of Pesticide Regulation for pesticides
used throughout the state. Such fux and drift studies have been conducted
for methyl bromide, emitted to the air after fumigation (see Chapter 8 for a
detailed example for methyl bromide applied to soil); parathion and chlorpyrifos, emitted from treated orchards; and toxaphene use in cotton felds
(see Chapter 3) (Seiber and Woodrow, 1981; Woodrow et al., 1983, 1997, 2001).
DOI: 10.1201/9781003217602-10
177