Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 189

intervals specifi ed on the label (Table 5 ). Assuming high sensitivity (5th centile
on the species sensitivity distribution) to fl owable CPY, or using actual dose-
response relationships indicated that several species, particularly those that forage
extensively in crop fi elds such as the horned lark ( Eremophila alpestris ), blue
grosbeak ( Passerina caerulea ), and red-winged blackbird ( A. phoeniceus ) are at
intermediate or high risk in some crops (e.g., grape, grapefruit, orange) if treated at
the maximum application rates and minimum treatment intervals.

6.2 Modeled Chronic Risks from Flowable CPY

For all patterns of use, the probability of birds having a total daily intake exceeding
the LOEL was <2% (Table 6 ). For most patterns of use and bird species, the
probability of exceeding the NOEL was also small (<5%). However, several species
and crop combinations (e.g., vesper sparrow ( Pooecetes gramineus ) in alfalfa,
red-winged blackbird ( A. phoeniceus ) in orange) had probabilities of exceeding the
NOEL of approximately 20%. The latter scenarios generally involved bird species
that forage frequently in treated fi elds and crops with high maximum application
rates (orange) or number of applications (alfalfa). In general, CPY poses little risk
to birds from chronic exposure.

6.3 Results of Field Studies for Flowable CPY

Corn . Studies were performed with Lorsban 4E (a fl owable formulation) on corn
fi elds in Warren and Madison counties, Iowa (Frey et al. 1994 ). Lorsban 4E was
applied at 3.36 kg ha −1 (3 lb ai A −1 ) during the pre-plant stage (ground broadcast),
and at 1.7 kg ha −1 (1.5 lb ai A −1 ) during the emergence (ground broadcast), whorl
(aerial broadcast) and tassel (aerial broadcast) stages. Monitoring of fi elds for birds
exhibiting signs of toxicity was done prior to each application and for 13-d following
each application, including abundance determinations, carcass search effi ciency
evaluations, and residue analyses.
Following pre-plant and at-plant applications, collection of moribund birds did not
reveal differences among the treated and control fi elds and invertebrates collected
during this period did not have detectable CPY residues. Applications during the
emergence test period caused no statistically signifi cant differences in the numbers
of dead birds found, but the casualty rate was higher in treated fi elds (0.14 casualties
per search) than in control fi elds (0.04 casualties per search).
During the whorl test period, bird censuses and mortality rates were similar in
control and treated fi elds. Following tassel stage application, bird censuses did not
reveal any differences in mortality among fi elds. Two robins ( Turdus migratorius )
collected from the fi elds treated with fl owable CPY exhibited signs of toxicity con-
sistent with inhibition of cholinesterase activity. One bird died, while the other bird
recovered and was released.