104
Pesticides, Organic Contaminants, and Pathogens in Air
a very few cases are atmospheric vapor transformations rapid enough to be
of signifcance in the time scale of minutes or hours; such cases include, merphos oxidation to S,S,S-tributyl phosphorotrithioate (DEF), OP thion oxidation to the corresponding oxon, and trifuralin N-dealkylation. At the other
end of the spectrum are chemicals such as dichlorodiphenyldichloroethylene
(DDE) and methyl bromide. Methyl bromide has a tropospheric lifetime of
approximately 1 year, which allows this chemical to diffuse, unreacted, to the
stratosphere (Yvon‐Lewis and Butler, 1997).
Dry deposition involves the settling of particles, which is strongly infuenced by particle size and the nature of the meteorology and terrain, and
by direct vapor-surface exchange. Wet deposition includes the scavenging
of particle-bound pesticides and pesticide vapors into atmospheric moisture (cloud- and fogwater, rain, and snow), followed by rainfall, snowfall,
or fog droplets coalescing on surfaces. This is potentially a major sink
for airborne pesticides, a source of exposure to pesticides for vegetation,
aquatic organisms, and watershed ecosystems, and a means of degrading
hydrolytically labile airborne pesticides. The content of pesticides in rain,
cloud, fog, and snow has been studied extensively only in the past 25 years
(Rice, 1996). The accumulating information is quite compelling. Pesticides
are measurably present in air and rainfall sampled throughout the United
States (Goolsby et al., 1994; Majewski and Capel, 1995). Pesticides are also
found in snow and ice, including in remote regions of the earth (Kurtz,
1990). And pesticides used (emitted) in the southeast or southern United
States ride the storm fronts presenting major deposition inputs to the
Chesapeake Bay (Glotfelty et al., 1990a), Great Lakes (Eisenreich et al.,
1981), and other water bodies. Pesticides and other anthropogenic trace
organics are found in cloud- and fogwater where they may achieve concentrations even greater than those expected based upon vapor–water distribution calculations (Glotfelty et al., 1987).
Fogwater residues in particular have been implicated as sources of inadvertent residues to nontarget crops (Turner, 1989) and of high-risk exposures
for hawks residing around treated orchards and for pumas and other predators which frequent water sources in coastal areas which receive marine salt
water sprays from the surf (Wilson et al., 1991). Fogwater is also an indicator
of long-range transport of pesticides to remote regions of the earth (Chernyak
et al., 1996). The present chapter will delve into the data and underlying
methodology associated with these fndings.
7.3 Pesticide Use in California
The coastal valleys of California, including the Central Valley, receive
extensive year-round use of a variety of pesticides and frequent occurrence
Pesticides, Organic Contaminants, and Pathogens in Air
a very few cases are atmospheric vapor transformations rapid enough to be
of signifcance in the time scale of minutes or hours; such cases include, merphos oxidation to S,S,S-tributyl phosphorotrithioate (DEF), OP thion oxidation to the corresponding oxon, and trifuralin N-dealkylation. At the other
end of the spectrum are chemicals such as dichlorodiphenyldichloroethylene
(DDE) and methyl bromide. Methyl bromide has a tropospheric lifetime of
approximately 1 year, which allows this chemical to diffuse, unreacted, to the
stratosphere (Yvon‐Lewis and Butler, 1997).
Dry deposition involves the settling of particles, which is strongly infuenced by particle size and the nature of the meteorology and terrain, and
by direct vapor-surface exchange. Wet deposition includes the scavenging
of particle-bound pesticides and pesticide vapors into atmospheric moisture (cloud- and fogwater, rain, and snow), followed by rainfall, snowfall,
or fog droplets coalescing on surfaces. This is potentially a major sink
for airborne pesticides, a source of exposure to pesticides for vegetation,
aquatic organisms, and watershed ecosystems, and a means of degrading
hydrolytically labile airborne pesticides. The content of pesticides in rain,
cloud, fog, and snow has been studied extensively only in the past 25 years
(Rice, 1996). The accumulating information is quite compelling. Pesticides
are measurably present in air and rainfall sampled throughout the United
States (Goolsby et al., 1994; Majewski and Capel, 1995). Pesticides are also
found in snow and ice, including in remote regions of the earth (Kurtz,
1990). And pesticides used (emitted) in the southeast or southern United
States ride the storm fronts presenting major deposition inputs to the
Chesapeake Bay (Glotfelty et al., 1990a), Great Lakes (Eisenreich et al.,
1981), and other water bodies. Pesticides and other anthropogenic trace
organics are found in cloud- and fogwater where they may achieve concentrations even greater than those expected based upon vapor–water distribution calculations (Glotfelty et al., 1987).
Fogwater residues in particular have been implicated as sources of inadvertent residues to nontarget crops (Turner, 1989) and of high-risk exposures
for hawks residing around treated orchards and for pumas and other predators which frequent water sources in coastal areas which receive marine salt
water sprays from the surf (Wilson et al., 1991). Fogwater is also an indicator
of long-range transport of pesticides to remote regions of the earth (Chernyak
et al., 1996). The present chapter will delve into the data and underlying
methodology associated with these fndings.
7.3 Pesticide Use in California
The coastal valleys of California, including the Central Valley, receive
extensive year-round use of a variety of pesticides and frequent occurrence