Drift
181
consists of a network of canals, streams, fooded and submerged or irrigated
felds. Pesticides from the agricultural regions of the Central Valley volatilize
and drift from warm parts of the valley to cooler high elevation regions of
the Sierra Nevada Mountains. Eventually the airmass moves to the foothill of
the Sierra’s and then to higher elevations of the western slopes of the Sierra’s.
During transport, pesticides undergo degradation and are scrubbed from
the air by wet/dry deposition. Wet deposition via snow and rain is prevalent during winter and spring. The fnal destinations of deposited pesticides
and/or pesticide degradation products are to surface waters, soil (and eventually groundwater), plant surfaces, and biota.
In one study, high volume air samples were collected, in addition to dry
deposition and surface waters at various points in the valley and Sequoia
National Park (118—3,322 m elevation) (LeNoir et al., 1999). Surface waters
contained residues of trifuralin, diazinon, chlorothalonil, chlorpyrifos, chlorpyrifos oxon, malathion, and endosulfan I/II. Those most heavily used in
summertime: trifuralin, chlorpyrifos, and endosulfan, were the most abundant in surface waters. Air samples additionally contained endosulfan sulfate;
whereas only chlorothalonil, chlorpyrifos, chlorpyrifos oxon, and endosulfan I/II were detected in dry deposition samples. Tested fsh species (trout
and stonefy) had concentrations well below 96-hour LC 50 values, but only the
more sensitive amphipods would likely suffer from the effects at these levels.
A series of studies have confrmed the long-range transport of PCBs that
contaminate water bodies, as opposed to coming from local sources. A transect study of the lakes and streams of the Tahoe Basin and Lake Tahoe itself
detected PCBs in both water and biota (trout) with similar profles (Datta
et al., 1998a). In a companion study, PCB congener profles were compared
between Lake Tahoe and Marlette Lake and were found to be the same. Since
Marlette Lake is isolated and off-limits to vehicles and recreational fshing, and monitored by the Nevada Division of Wildlife, detected PCBs were
attributed to long-distance transport as opposed to being generated from
local sources (Datta et al., 1998b).
Decline of sensitive amphibian populations in the Sierra Nevada has been
attributed to drift of PCBs and chlorinated pesticides such as dichlorodiphenyltrichloroethane (DDT) and toxaphene, which may act as endocrine disrupters (National Pesticide Information Center, 2020). Earlier studies sampled frogs
from the Sierra Nevada Mountains and found measurable dichlorodiphenyldichloroethylene (DDE) which provided evidence of DDT contamination
from prior years (Cory et al., 1970). DDT was banned in 1972 but its residues
persist, especially its long-lived breakdown product, DDE. A concentration
gradient was noted: frogs in the western slopes of the mountains had higher
concentrations of DDT/DDE, indicating they originated from California’s central valley. However, in the case of toxaphene, which was used heavily in the
cotton felds of California before 1975, the low levels detected in pacifc tree
frogs downwind of the source did not provide convincing evidence linking
declining populations to toxaphene drift (Angermann et al., 2002).
181
consists of a network of canals, streams, fooded and submerged or irrigated
felds. Pesticides from the agricultural regions of the Central Valley volatilize
and drift from warm parts of the valley to cooler high elevation regions of
the Sierra Nevada Mountains. Eventually the airmass moves to the foothill of
the Sierra’s and then to higher elevations of the western slopes of the Sierra’s.
During transport, pesticides undergo degradation and are scrubbed from
the air by wet/dry deposition. Wet deposition via snow and rain is prevalent during winter and spring. The fnal destinations of deposited pesticides
and/or pesticide degradation products are to surface waters, soil (and eventually groundwater), plant surfaces, and biota.
In one study, high volume air samples were collected, in addition to dry
deposition and surface waters at various points in the valley and Sequoia
National Park (118—3,322 m elevation) (LeNoir et al., 1999). Surface waters
contained residues of trifuralin, diazinon, chlorothalonil, chlorpyrifos, chlorpyrifos oxon, malathion, and endosulfan I/II. Those most heavily used in
summertime: trifuralin, chlorpyrifos, and endosulfan, were the most abundant in surface waters. Air samples additionally contained endosulfan sulfate;
whereas only chlorothalonil, chlorpyrifos, chlorpyrifos oxon, and endosulfan I/II were detected in dry deposition samples. Tested fsh species (trout
and stonefy) had concentrations well below 96-hour LC 50 values, but only the
more sensitive amphipods would likely suffer from the effects at these levels.
A series of studies have confrmed the long-range transport of PCBs that
contaminate water bodies, as opposed to coming from local sources. A transect study of the lakes and streams of the Tahoe Basin and Lake Tahoe itself
detected PCBs in both water and biota (trout) with similar profles (Datta
et al., 1998a). In a companion study, PCB congener profles were compared
between Lake Tahoe and Marlette Lake and were found to be the same. Since
Marlette Lake is isolated and off-limits to vehicles and recreational fshing, and monitored by the Nevada Division of Wildlife, detected PCBs were
attributed to long-distance transport as opposed to being generated from
local sources (Datta et al., 1998b).
Decline of sensitive amphibian populations in the Sierra Nevada has been
attributed to drift of PCBs and chlorinated pesticides such as dichlorodiphenyltrichloroethane (DDT) and toxaphene, which may act as endocrine disrupters (National Pesticide Information Center, 2020). Earlier studies sampled frogs
from the Sierra Nevada Mountains and found measurable dichlorodiphenyldichloroethylene (DDE) which provided evidence of DDT contamination
from prior years (Cory et al., 1970). DDT was banned in 1972 but its residues
persist, especially its long-lived breakdown product, DDE. A concentration
gradient was noted: frogs in the western slopes of the mountains had higher
concentrations of DDT/DDE, indicating they originated from California’s central valley. However, in the case of toxaphene, which was used heavily in the
cotton felds of California before 1975, the low levels detected in pacifc tree
frogs downwind of the source did not provide convincing evidence linking
declining populations to toxaphene drift (Angermann et al., 2002).