Refined Avian Risk Assessment for Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 165

Risk (STIR), version 1.0, we determined that inhalation of CPY would not be a
signifi cant exposure pathway for birds. In that analysis, airblast application at the
largest permitted, single application rate on the Lorsban Advanced label (i.e.,
6.23 kg ha −1 (5.6 lb ai A −1 for oranges)), and a vapor pressure of 0.0000202 mm Hg
(0.00269 Pa) (Solomon et al. 2014 ; USEPA 2009 ) were assumed. When the pre-
dicted exposure was compared to the lowest oral LD 50 for birds, i.e., 5.62 mg ai kg −1
bwt for common grackle (Schafer and Brunton 1979 ), the results of STIR predicted
that exposure via inhalation “is not likely signifi cant” for birds exposed to CPY on
treated fi elds immediately after application at the maximum permitted rate on the
label for Lorsban Advanced. Thus, the most important routes of exposure for birds
following application of fl owable CPY are ingestion of residues on food items
and ingestion of water from on-fi eld puddles and other drinking water sources
(e.g., dew). These routes of exposure were the focus of the avian risk assessment
for fl owable CPY.
Following application of the fl owable formulation, CPY can reach offsite soil,
water bodies, terrestrial vegetation, and insects from spray drift, runoff and erosion
(Williams et al. 2014 ). Some CPY will dissipate into the air, either becoming air-
borne during application or volatilizing from treated surfaces (Mackay et al. 2014 ).
Chlorpyrifos in air may be transported by wind and deposited offsite, but amounts
will be small (Mackay et al. 2014 ). Direct application of CPY to streams, lakes, and
ponds is not permitted by product labels. Because exposure will be greatest on
treated fi elds, assessment of risks of fl owable CPY to birds was estimated for birds
foraging on-fi eld. Risks to birds foraging off-fi eld would be much less.
Following application of granular CPY, unincorporated and intact granules might
be directly ingested by birds while they are foraging for grit (Luttik and de Snoo
2004 ; Moore et al. 2010b , c ). When water has collected on the soil surface where
granules have been applied, birds might ingest dissolved CPY from pooled water.
However, farmers do not normally apply granular pesticides when soil is saturated
with water or when signifi cant precipitation is expected within a day or two of appli-
cation. Exposure via dermal contact is expected to be minimal because the CPY that
exists in granules is unlikely to be available for transport across feathers and the bird
epidermis. This assumption is supported by the results of a study involving penned
turkeys ( M. gallopavo ) that were exposed to 5% CPY in granules applied to soil at
a rate of 3.36 kg ha −1 (3 lb ai A −1 ) (Price et al. 1972 ). The only labeled crop having
a higher maximum application rate for granular CPY (Lorsban 15G) is peanuts
(i.e., 4.48 kg ha −1 ). No toxicity occurred during the 4-wk study, indicating that
turkeys did not accumulate signifi cant amounts of CPY through their feet or feath-
ers. Thus, the focus of the assessment of for the granular formulation was on birds
exposed to CPY granules while foraging for grit to aid digestion.

2.5 Toxicity and Mode of Action

As with other organophosphorus pesticides, CPY is rapidly absorbed following
ingestion in food and water. It then undergoes oxidative metabolism to form CPYO,