Carbaryl, Carbofuran, and Methomyl - National Marine Fisheries ...

compared to abundances at the reference sites following applications. Interestingly, reductions
in biodiversity in 2001 agricultural sites compared to reference sites was not seen in 2002 (Van
der Linde 2005). The authors commented that diversity metrics do not always behave
consistently or predictably in response to environmental stress. More than two years of data are
likely needed to more sufficiently address community variability at this site.
Two sets of field experiments directly investigated juvenile steelhead (hatchery- reared) AChE
activity from caged-fish studies in an agricultural basin in Hood River Basin, OR (Grange 2002;
St. Aubin 2004). The studies analyzed water samples for chlorpyrifos, azinphos-methyl, and
malathion before, during, and after orchard spray periods. One of the studies also monitored the
aquatic invertebrate community’s response (discussed later under prey effects) in conjunction
with the AChE inhibition (St. Aubin 2004). Steelhead from reference sites had statistically
significantly greater AChE activity than steelhead from orchard-dominated areas. The
reductions in AChE activity corresponded to the application seasons and detections of
chlorpyrifos and azinphos-methyl insecticides.
The data from one study indicated that OP-insecticides inhibited AChE activity in steelhead held
in cages in the Hood River Basin and this inhibition correlated to chlorpyrifos and azinphosmethyl
detections and to a lesser degree with malathion detections (Grange 2002). None of the
pesticides were detected at reference sites and both chlorpyrifos (range in maxima of (0.077-
0.196 µg/L) and azinphos-methyl were frequently detected at orchard stream and river sites.
AChE activity was inhibited up to 21% in smolts, and 33% in juveniles relative to reference
locations. Temperature was a confounding factor as lower temperatures showed lower AChE
activity while higher temperatures showed higher AChE activity at reference sites. The authors
normalized data to temperature and found a greater number of statistically significant reductions
in AChE in steelhead. Study results show that steelhead in these systems exposed to OP
insecticides lose AChE activity (up to 33%) which, depending on the percentage of inhibition,
can manifest into fitness level consequences (Grange 2002; St. Aubin 2004).
The field studies conducted in Hood River Basin, Oregon show that salmonids’ AChE activity
was reduced in streams near orchards during chlorpyrifos and azinphos-methyl applications.
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