Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 238

contains a high concentration of CPY and is available for extended intervals of time
during the day. For example at the rate for peppermint, a 1 cm ha −1 irrigation with
an application at 2.12 kg ha −1 (1.88 lb A −1 ) would give a dose of over 600 ng bee −1
for a typical uptake of 30 μL of water by a foraging bee in a single trip. This amount
would be lethal, and foraging honey bees would not make it back to the hive to
recruit more foragers to the wet foliage as a water source.

Other routes of exposure . Davis and Williams ( 1990 ) extended the typical approach
of calculating intrinsic toxicity levels and field application rates to consider buffer
zones downwind of sprayed areas and provide an estimates of the distance at which
bees would encounter an LD 50 dose from spray drift. These distances were deter-
mined using published data on spray depositions under various weather conditions
for ground and aerial sprays of crops in Britain. They concluded that ground spray-
ing of CPY at typical application rates would result in exposures of honey bees at
the LD 50 within 36-46 m of the application site at a wind speed of 4 m sec −1
(14.4 km h −1 ). Labels for products containing CPY state that sprays are not to be
applied when wind speed exceeds 16 km h −1 .
Only one reference on potential toxicity of CPY vapor to pollinators was found,
indicating that vapor of Lorsban WP (50% CPY) applied at 0.56 kg product ha −1
should not have effects on honey bees (Clinch 1972 ). There are no fumigant prod-
ucts based on CPY. While the lipophilicity of CPY (log K OW = 5.0) (Solomon et al.
2014 ) is high enough to make accumulation of CPY in honey bee wax from air
plausible, the concentrations in air are very small and ephemeral. A maximum of
250 ng m −3 has been reported (Mackay et al. 2014 ). There is little evidence to sup-
port the possibility of accumulation of concentrations in wax in the hive from trace
concentrations in the air.

4 Toxicity of CPY to Pollinators

4.1 Tier-1 Tests of Effects

Acute toxicity to A. mellifera . Acute toxicity of CPY to A. mellifera has been deter-
mined, and acute topical LD 50 values ranged from 0.024 μg bee −1 to 0.55 μg bee −1
(Table 6 ). A. mellifera appears to be slightly less sensitive to CPY by the dietary
route, with oral LD 50 values ranging from 0.114 μg bee −1 with technical product, to
2.15 μg bee −1 of formulated product (18.7% CPY) (Table 7 ).
One study was found that reported the acute toxicity of CPY to honey bee larvae.
Atkins and Kellum ( 1986 ) carried out studies to determine the potential hazard to
honey bee brood of pesticide contaminated food in the hive. Pesticides were added
to individual brood cells followed by monitoring of effects throughout the brood
cycle and into the adult stage. This resulted in a combined oral and cuticular exposure.
For CPY (Lorsban 4E), 5-6 day-old larvae were the most susceptible age-group,
whereas 1-2 day-old larvae were the least susceptible. The recorded LD 50 values for