118
Pesticides, Organic Contaminants, and Pathogens in Air
food and water, and dermal intake through talons are all routes for exposure.
It may all contribute to a residue exposure suffciently high to produce biochemical and clinical signs of organophosphorus intoxication (Hooper et al.,
1989; Wilson et al., 1991).
If one considers fog as simply one type of cloud, then the signifcance of
fog- or cloudwater accumulation and transport of pesticides and other contaminants may assume a regional or global signifcance. The potential for
regional or long-range transport and deposition of Valley-derived OPs used
in dormant spraying is an example. Chlorpyrifos, diazinon, and parathion
and their oxons were detected in air, rain, and snow samples collected in
December–March in the Sierra Nevada Mountains southeast of the San
Joaquin Valley orchard regions (Zabik and Seiber, 1993). Air concentrations at
pg/m 3 levels were determined at elevations of 533 and 1,920 m in the mountains. Rainwater concentrations were at ppt (ng/L) levels at the mountain
sites. Clearly, long-range transport of OPs can occur, but the indications are
that removal processes (exchange with soil and plant surfaces, wet deposition, and chemical breakdown via oxon formation followed by hydrolysis)
operating in the Valley itself may limit the buildup of OPs at nontarget sites
outside the Valley.
Recently a number of pesticides and PCBs were detected in snow and some
surface waters in the Sierra Nevada Mountains, apparently resulting from
wet deposition of residues in clouds (McConnell et al., 1998). The signifcance
of these aerially transported residues warrants further investigation (Seiber
and Woodrow, 1998).
7.7 Conclusions
Fog represents an atmospheric medium in which pesticides may be degraded
or undergo vapor–liquid distribution, and subsequent deposition. It probably does not alone present a direct health hazard to humans, but it will add to
total exposure from ingestion of pesticides in food crops and drinking water,
and residential exposure. Fogwater residues may have a major health impact
on animals which reside in or around pesticide-treated areas, from deposition to their feathers or fur. More work is needed to defne risks associated
with pesticides, as well as other toxicants in foggy atmospheres.
Pesticide residues found in rainwater are frequently reported by the U.S.
Geological Service as relevant to fog. Such residues are generally low compared with fogwater but result in runoff to lakes, streams, and other local
waterways.
Text of this chapter was Reproduced with permission from Seiber, J.N. and
Woodrow, J.E. (2000). Transport and Fate of Pesticides in Fog in California’s
Central Valley. In Agrochemical Fate and Movement, T.R. Steinheimer, L.J.
Pesticides, Organic Contaminants, and Pathogens in Air
food and water, and dermal intake through talons are all routes for exposure.
It may all contribute to a residue exposure suffciently high to produce biochemical and clinical signs of organophosphorus intoxication (Hooper et al.,
1989; Wilson et al., 1991).
If one considers fog as simply one type of cloud, then the signifcance of
fog- or cloudwater accumulation and transport of pesticides and other contaminants may assume a regional or global signifcance. The potential for
regional or long-range transport and deposition of Valley-derived OPs used
in dormant spraying is an example. Chlorpyrifos, diazinon, and parathion
and their oxons were detected in air, rain, and snow samples collected in
December–March in the Sierra Nevada Mountains southeast of the San
Joaquin Valley orchard regions (Zabik and Seiber, 1993). Air concentrations at
pg/m 3 levels were determined at elevations of 533 and 1,920 m in the mountains. Rainwater concentrations were at ppt (ng/L) levels at the mountain
sites. Clearly, long-range transport of OPs can occur, but the indications are
that removal processes (exchange with soil and plant surfaces, wet deposition, and chemical breakdown via oxon formation followed by hydrolysis)
operating in the Valley itself may limit the buildup of OPs at nontarget sites
outside the Valley.
Recently a number of pesticides and PCBs were detected in snow and some
surface waters in the Sierra Nevada Mountains, apparently resulting from
wet deposition of residues in clouds (McConnell et al., 1998). The signifcance
of these aerially transported residues warrants further investigation (Seiber
and Woodrow, 1998).
7.7 Conclusions
Fog represents an atmospheric medium in which pesticides may be degraded
or undergo vapor–liquid distribution, and subsequent deposition. It probably does not alone present a direct health hazard to humans, but it will add to
total exposure from ingestion of pesticides in food crops and drinking water,
and residential exposure. Fogwater residues may have a major health impact
on animals which reside in or around pesticide-treated areas, from deposition to their feathers or fur. More work is needed to defne risks associated
with pesticides, as well as other toxicants in foggy atmospheres.
Pesticide residues found in rainwater are frequently reported by the U.S.
Geological Service as relevant to fog. Such residues are generally low compared with fogwater but result in runoff to lakes, streams, and other local
waterways.
Text of this chapter was Reproduced with permission from Seiber, J.N. and
Woodrow, J.E. (2000). Transport and Fate of Pesticides in Fog in California’s
Central Valley. In Agrochemical Fate and Movement, T.R. Steinheimer, L.J.