Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 249

Table 12 Tier-2 risk quotients (RQs) for oral exposure of honey bees to chlorpyrifos (CPY) via
pollen

Larvae (120 mg) Adults (292 mg)

Variable Median 95th centile Median 95th centile

Dose (μg CPY
bee −1 ) a

5.26 × 10 −4 2.72 × 10 −2 1.28 × 10 −3 6.61 × 10 −2

LD 50 b 0.146 0.146 0.114 0.114

RQ c 0.004 0.19 0.011 0.580

a Reported in Table 3
b Technical CPY reported in Table 7 and larvae LD 50 derived from Atkins and Kellum ( 1986 )
c Risk Quotient = Dose/LD 50 where LD 50 = 0.146 or 0.114 μg bee −1

(Table 3 ). The estimates of oral exposure and the oral LD 50 values of 0.114 μg
adult −1 bee and 0.146 μg larva −1 (Atkins and Kellum 1986 ) provided RQ values
below the LOC of 0.4 for median acute exposures. The 95th centile exposure and
larval LD 50 give an RQ below the LOC, but a RQ slightly above the LOC when the
adult LD 50 was used (Table 12 ). Based on analysis of CPY in nurse bees (Table 10 )
fed exclusively a diet of pollen containing CPY at a concentration of 955 μg kg −1
(DeGrandi-Hoffman et al. 2013 ), doses were 7.5 × 10 −3 and 6.8 × 10 −3 μg bee −1
(93 mg) for the two parallel experiments, which would be equivalent of approxi-
mately 7% of the LD 50 for technical grade CPY (Table 7 ). The authors did not
describe symptoms of toxicity in nurse bees so they were apparently unaffected.
The RQ for adults, based on the 90th centile concentration of 140.4 μg kg −1
reported by Mullin et al. ( 2010 ), is 0.36. Therefore, dietary exposure of adult honey
bees to CPY is expected to be below the LOC >90% of the time, while exposures
for larvae should be below the LOC >95% of the time. Considering that most pollen
samples (56%) collected by Mullin et al. ( 2010 ) did not contain CPY, oral exposure
to CPY should be of low risk to honey bees, particularly in terms of the protection
goals of overall fitness of the colony.
Mullin et al. ( 2010 ) did not measure concentrations of pesticides in honey and no
studies were found which examined concentrations of CPY in nectar. Only one
study was from Uruguay reported detection of CPY in honey. The mean and maxi-
mum concentrations of CPY in honey samples that were positive for CPY (42%)
were 46 and 80 μg kg −1 , respectively (Pareja et al. 2011 ). Using the recommended
consumption rates of 120 mg honey d −1 for larvae and 292 mg honey d −1 for adults,
honey bee larvae exposed to a concentration of 80 μg CPY kg −1 honey would con-
sume 0.0096 μg CPY d −1 , whereas adults would be expected to consume 0.023 μg
d −1 . At an LD 50 of 0.114 μg bee −1 , corresponding RQ values for larvae and adults
would be 0.08 for larvae and 0.2 for adults. These values are below the LOC of 0.4
and suggest little risk to honey bees from acute exposure to CPY via honey.
Exposure estimates through consumption of nectar and pollen are assumed to be
conservative representations of potential exposures through honey and bee bread,
respectively (USEPA 2012 ). The estimates assume that pesticides do not degrade
while honey and bee bread are stored in the hive. They also assume that rates of
consumption of pollen and nectar and resulting exposures are protective of