Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 229

Table 1 Tier-1 estimates of chlorpyrifos (CPY) dietary exposure in honey bees (aggregate nectar
and/or honey and pollen consumption) during foliar applications of Lorsban 4E or Lorsban
Advanced at minimum and maximum application rates based on T-REX estimates of concentrations
in pollen and nectar
Life stage Minimum dose (μg CPY bee −1 ) Maximum dose ( μ g CPY bee −1 )

Adult 7.5-61 30.5-183

Larvae 3.1-25 12.6-75

Estimates of post - application residual contact exposure . Post-application contact
exposure for bees is mainly from exposure to residues on the surface of flowers that
were open during application and remain attractive to bees after application, since
they are attracted to flowers and do not typically land on leaves or other plant sur-
faces (Willmer 2011 ) (Fig. 1 ). An estimate of the concentration of CPY on the sur-
faces of plants in units of mass per unit area (e.g., μg cm 2 ) is required for comparison
to the measured endpoint from standard contact toxicity tests. The USEPA guideline
does not provide a Tier-1 estimate for this scenario (USEPA 2012 ). The Kenaga
nomogram, as revised by Fletcher et al. ( 1994 ), was developed to provide an estimate
of exposure on vegetation after application of a pesticide. However, the estimate is
in mg AI kg −1 fresh weight, making it unsuitable for estimates of post-application
contact exposure.

3.4 Tier-2 Characterization of Exposure

Estimates of dietary exposure from field data . Applications of CPY outside the flow-
ering period would not be expected to result in exposure of bees through nectar and
pollen, but some flowers, including those on weeds that were open during spray
application, may remain available to foraging pollinators after application, leading
to both contact and dietary exposure of adult foragers.
No data on concentrations of CPY in pollen and nectar manually collected in the
field were found. However, several studies screened pollen or honey collected from
honey bee hives for pesticides, including CPY. A broad survey of concentrations of
pesticide in samples collected from honey bee hives across 23 states in the U.S., one
Canadian province, and several agricultural cropping systems during the 2007-2008
growing season was conducted by Mullin et al. ( 2010 ). The survey included both
migratory hives moved to multiple crops for pollination and non-migratory hives.
Of the 118 pesticides and metabolites surveyed, CPY was the most frequently found
insecticide other than those used in the hive as acaricides for mite control, and the
third-most detected compound in trapped pollen or beebread samples (153 of 350
samples). The mean concentration was 53.3 ± 10.6 (SEM) μg kg −1 in those samples
that had positive detects (Table 2 ). Median and 95th centile CPY pollen concentra-
tions reported by Mullin et al. ( 2010 ) were based on calculations that included
non-detections.