Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 188

we used a conservative approach and derived a NOEL and LOEL from the most
sensitive species tested to date, viz., the mallard ( A. platyrhynchos ). In a 1-generation
reproduction study (Fink 1978a ), reduced reproductive success was observed at a
concentration of 125 mg ai kg −1 diet but no adverse effects were observed at a con-
centration of 25 mg ai kg −1 diet. The primary response observed when birds were
exposed to 125 mg ai kg −1 diet was fewer eggs laid per hen. Therefore, rate of intake
of food and body mass during the egg-laying phase of the study (i.e., the fi nal 8-wk)
were used as the measurement endpoints upon which to base the dietary NOEL and
LOEL. Mean rates of intake of food at doses equivalent to the NOEC and LOEC
were 0.134 and 0.140 kg diet bird −1 d −1 , respectively. The corresponding average body
masses were 1.12 and 0.934 kg bwt, respectively. The resulting dose-based NOEL
and LOEL are 2.99 and 18.7 mg ai kg −1 bwt d −1 , respectively. The NOEL and LOEL
were used as thresholds for chronic effects in this refi ned assessment of risk.

6 Risk Characterization for Flowable Chlorpyrifos

For each acute exposure scenario, the fate of each bird was determined by con-
verting estimated maximum retained dose to a standard normal Z score from the
appropriate dose-response curve and comparing that value to a randomly drawn
value from a uniform distribution with a range of 0-1 (see Sect. 3.2 ). This process
was repeated for 20 individuals of each species on each of 1,000 fi elds. Results were
then expressed as a risk curve indicating the percentage of fi elds that had 5%
mortality (1/20 birds died), 10% mortality (2/20 birds died), 15% mortality (3/20
birds died), etc. The Ecological Committee on FIFRA Risk Assessment Methods
(ECOFRAM 1999 ) referred to such plots as “joint probability curves” while others
refer to these plots as “risk curves” (e.g., Giddings et al. 2005 ; Moore et al.
2010a , b ). For chronic exposure scenarios, risk was characterized by determining
the probabilities that exposure exceeded the NOEL and LOEL for the most sensitive
species tested.
The dose-response curve used to estimate acute risk depended on the focal
species. If a dose-response curve was available for the focal species of interest, that
curve was used (i.e., northern bobwhite ( C. virginianus ), red-winged blackbird
( A. phoeniceus )). In the absence of species-specifi c dose-response curves, acute
dose-response curves were generated for three hypothetical species representing a
range of sensitivities (Fig. 7 ).

6.1 Modeled Acute Risks from Flowable CPY

The modeling for fl owable CPY indicated that, with one exception, all bird species
were at low or de minimis risk if they had median or lesser sensitivity to fl owable
CPY applied to alfalfa, almond, apple/cherry, broccoli, corn, grape, grapefruit,
orange, pecan, soybean or sweet corn at the maximum application rates and minimum