Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 250

exposures through consumption of royal jelly and brood food, since concentrations
of pesticides in food consumed by nurse bees are 2-4 orders of magnitude greater
than concentrations measured in royal jelly (Davis and Shuel 1988 ).
Estimated risk through consumption of water . Pollinators can be exposed to CPY in
drinking water from small ponds, puddles, or on foliage wet from rain or dew.
Exposure from wet foliage occurs with sprayable formulations only, while exposure
from puddles or small ponds occurs with both sprayable and granular formulations
of CPY. Using the modified rice paddy model recommended by USEPA to provide
estimates of pesticide exposure to bees through puddles in treated fields, estimated
worst-case daily doses of CPY in puddles were <2.4 × 10 −7 μg CPY bee −1 . With the
oral LD 50 value of 0.114 μg CPY bee −1 , this provides a RQ of 2.1 × 10 −6 (Table 13 ),
which is well below the LOC of 0.4, indicating a de minimis risk to pollinators rela-
tive to other potential exposure routes.
Using the PRZM/EXAMS puddle 95th centile concentrations, which apply to
both sprayable and granular applications of CPY, the predicted peak concentrations
were much higher than the values obtained using the Tier-1 rice paddy model, since
they include storm runoff events within hours after application. It is unlikely that
bees would be exposed to these concentrations as storm events are rare, and such
events within hours after application are even less common. Bees are not likely to
go into fields to collect water, given the high humidity and availability of water
around a hive after such a storm.
The model recommended by the USEPA to predict concentrations of pesticide in
dew estimated a worst-case dose of 0.034 μg CPY bee −1 (USEPA 2012 ). This model
and dose also provides a RQ less than the LOC (Table 13 ) and suggests low risk to
pollinators through consumption of contaminated dew. This scenario also applies to
wet foliage from rain or irrigation as well as from dew. Residues of CPY in dew
come from the leaf surface, and the concentration is determined by partition between
the leaf surface and the water. The maximum potential concentration occurs when
there is no runoff of rain or dew to carry material away from the leaf. As water dries,
the residues partition back onto the leaf surface. Summation of exposures via food
and water from Tables 12 and 13 also suggests that the risks from the combined
sources would be small for most bees.
As described in the exposure section, honey bees may collect water for direct
consumption, to prepare food, or to control temperature in the colony. Assuming
transport of 1,250 mg d −1 of water to the colony from a source such as a puddle or
250 mg d −1 from a more temporary source such as dew, with 100% uptake of CPY
from the water being carried, the modified USEPA puddle model gave an RQ well
below the LOC (Table 13 ), but the dew model gave an RQ of 1.6. The RQ values
calculated from puddle concentrations obtained using the PRZM/EXAMS model
also exceeded the LOC (Table 13 ). These values are based on conservative approx-
imations, and in the case of the PRZM/EXAMS predictions, have low probability
of occurrence. Using the refinements in the Liqui-PARAM model, the 95th per-
centile RQ for collection of water from wet foliage was reduced to a level essen-
tially the same as the LOC. The median RQ for both the OCSPP model and the
Liqui-PARAM model estimates of exposure were well below the LOC (Table 13 ).