Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 187

5.4 Infl uence of Dietary Matrix on Acute Toxicity

In a standard acute LD 50 test, the test chemical is administered via gavage directly
into the esophagus or crop of the bird, usually with a carrier such as corn oil, a solvent
or water. Use of such carriers maximizes the potential for the chemical to be
absorbed rapidly, more so than would occur in the fi eld where the chemical is
bound to food items. When pesticides are mixed with food, or consumed at a time
when the gastrointestinal (GI) tract has other food items present, they are absorbed
less effi ciently than when dosed as a bolus in pure form into an empty GI tract
(Lehman-McKeeman 2008 ).
To examine effects of excipient on toxicity, Hubbard and Beavers ( 2009 ) admin-
istered CPY to 19-wk old northern bobwhite ( C. virginianus ) using either corn oil
or a feed slurry as the excipient. Groups of ten birds were randomly assigned to six
treatment groups ranging from 0 (control) to 60 mg ai kg −1 bwt. The dose was mixed
with the chosen excipient and orally intubated into the crop or proventriculus of
each bird. For corn oil as excipient, CPY was dispersed in corn oil, and for the feed
slurry excipient, treated food was mixed with water at a ratio of 1:2.5. Birds were
monitored for 14-d following dosing to evaluate effects on body weight, lethality,
consumption of food, appearance, and abnormal behavior. No signs of toxicity were
observed in control groups. When corn oil was used as the excipient, signs of toxicity
were fi rst observed in the 21.6 mg ai kg −1 bwt treatment group, and included a
ruffl ed appearance and lethargy. Body weight of female birds exposed to 21.6 mg
ai kg −1 bwt decreased as did body weights in both sexes in the greater dose groups.
Rate of consumption of food was reduced in males fed 36 mg ai kg −1 bwt and in
males and females fed 60 mg ai kg −1 bwt. The NOEL was 13.0 mg ai kg −1 bwt.
Lethality only occurred in birds fed 60 mg ai kg −1 bwt. Therefore, the LD 50 was
defi ned as >60 mg ai kg −1 bwt when corn oil was used as the excipient. When CPY
was diluted with feed slurry as the excipient, signs of toxicity were fi rst observed in
individuals exposed to 21.6 mg ai kg −1 bwt. The signs of toxicity included a ruffl ed
appearance and 1 lethality. Lethality skewed the observations for both change in
body mass and rate of consumption of food. However, a lesser body mass was
observed in surviving birds dosed at 21.6 mg ai kg −1 bwt or greater. Reduced con-
sumption of food was observed in female birds dosed at 21.6 and 36 mg ai kg −1 bwt.
The LD 50 was 29.0 mg ai kg −1 bwt and the NOEL was 13.0 mg ai kg −1 bwt. In this
study, the food-based slurry did not reduce toxicity compared to the corn oil excipient.
Therefore, the acute effects metrics derived above were not adjusted to account for
the dietary matrix consumed by birds in treated fi elds.

5.5 Chronic NOEL and LOEL

There is an insuffi cient number of studies to derive a chronic SSD for CPY. Further,
there are no chronic studies with a suffi cient number of treatments to enable derivation
of a dose-response curve. Given the paucity of chronic toxicity studies for birds,