Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 231

Table 3 Tier-2 estimates of chlorpyrifos (CPY) exposure through daily consumption of pollen
and nectar by adult and larval honey bees
Life stage
(consumption mg) Median dose ( μ g CPY bee −1 ) a 95th centile dose ( μ g CPY bee −1 ) b
Adult (292) 1.28 × 10 −3 6.61 × 10 −2
Larva (120) 5.26 × 10 −4 2.72 × 10 −2
a Based on median CPY detection in pollen of 4.4 μg kg −1 (Mullin et al. 2010 )
b Based on 95th centile CPY detection in pollen of 226.6 μg kg −1 (Mullin et al. 2010 )
in honey from just under half of analyzed samples, at a mean concentration similar
to that found in pollen in the U.S. by Mullin et al. ( 2010 ) (Table 2 ). CPY was detected
in honey in Brazil (Rissato et al. 2007 ) (Table 2 ), but the authors did not provide
details on the frequency of detection. CPY was not among the many pesticides
detected in honey collected from hives in France (Chauzat et al. 2011 ). Similarly,
CPY was not detected in honey samples collected from beekeepers in India, although
concentrations of organochlorine, cyclodiene, synthetic pyrethroids, and other
organophosphorus insecticides were found (Choudhary and Sharma 2008 ) (Table 2 ).
The Tier-1 estimates of exposures of 110 mg CPY kg −1 in nectar or pollen (per
1.12 kg −1 CPY ha −1 ) appear to be overly conservative (protective). From the data
reported by Mullin et al. ( 2010 ), CPY was not detected in most samples and, when
detected, it was at concentrations several orders of magnitude below the modeled
estimates from T-REX. Based on the data of Mullin et al. ( 2010 ) and the aggregate
pollen and nectar (honey) consumption rates for larvae (120 mg d -1 ) and adult
worker bees (292 mg d -1 ), the estimated dose of CPY received by honey bees would
be several orders of magnitude below the Tier-1 modeled estimates of 110 mg
CPY kg -1 from T-REX (Table 3 ).
The above estimates of oral exposure were based on daily consumption rates of
honey bees. There is greater uncertainty regarding rates of nectar and pollen con-
sumption for non- Apis bees. However, an analysis of data recently compiled by
EFSA ( 2012 ) suggests that adult honey bee workers and adult bumble bees have
similar consumption rates, while that of adult female European mason bees and
alfalfa leaf cutting bees is less. The same trends hold for larvae of these bees. Thus,
exposures estimated from consumption of pollen and nectar by adult honey bees
should be representative or protective of these non- Apis pollinators.
Estimates of post - application residual contact exposure on vegetation . Pollinators
can come in contact with residues of CPY on flowers or inflorescences, or in some
cases with extrafloral nectaries, following a spray application if flowers that were
open during application remain attractive to pollinators after application. This is
potentially a major route of exposure (Fig. 1 ). Residues on flowers are expected to be
similar to or less than those found in or on foliage. These will be greatest immedi-
ately after spraying of foliage and thereafter dissipate rapidly through volatilization,
photolysis, and dilution by growth of the plant. Residual contact exposure will also
decline with time as visits of pollinators to older flowers decrease and visits to newer
unsprayed flowers increase. This usually occurs within 1-3 d (Willmer 2011 ).