Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 222

is not used as a seed treatment, so there is no contribution from seed dust during
planting and there is no translocation and guttation. Volatilization of foliar residues
constitutes the most significant source of airborne contamination. However, residues
of CPY in air are not persistent, and maximum concentrations found in air monitor-
ing studies were less than 250 ng m −3 (Mackay et al. 2014 ), which, when compared
to the toxic dose in bees of about 80 ng bee −1 suggests that risks from exposure of
this type would be de minimis .
Thus, the main route of direct exposure for pollinators is the uptake of CPY from
plant surfaces after application. Residues of CPY applied as a spray on vegetation
are mostly on foliage, which includes any non-crop flowers open during application.
For example, white clover in turf or in groundcover under an orchard or areas adja-
cent to a treated field is very attractive to pollinators and can be in bloom during
foliar application (Barmaz et al. 2010 ). Pollen in flowers that were open during
application remains available for collection by pollinators for some time after treat-
ment, but concentrations of pesticides in pollen and on plant surfaces will decline
and become less bioavailable with time, particularly after sprays have dried. Nectar
and honeydew were grouped into a sub-compartment of vegetation. Direct oral tox-
icity due to exposure via nectar and honeydew are incomplete or minimal because
CPY is not systemic and is not taken up via roots and translocated upward through
the plant (Racke 1993 ). Relatively smaller amounts of CPY would be expected in
honey for the following reasons:

• Nectar is more protected than pollen from exposure to spray droplets by the

anatomy of flowers (Willmer 2011 ).

• Nectar, water, and honeydew are carried internally in the “honey stomach” by

bees (Gary 1975 ; Snodgrass 1975 ), where residues of pesticides are more likely
to be absorbed and metabolized, reducing the amount transferred to the hive.
Residues of CPY have been shown to decrease 3-fold when pollen is processed
into bee bread (DeGrandi-Hoffman et al. 2013 ).

• CPY present in nectar would be exposed to water, which would favor hydrolysis

and detoxification pathways over oxidation, and formation of CPYO (Solomon
et al. 2014 ).

• Forager bees are initially most exposed to residues in nectar since it is ingested

and those individuals could be impaired or killed by greater concentrations
before returning to a hive. This potential for toxic effects before returning to a
hive would be exacerbated by relatively greater loads of nectar (40-90 mg bee −1 )
compared to pollen (12-29 mg bee −1 ) per foraging trip (Gary 1975 ).

• Residues in honey in the hive are likely the result of transfer of residues from a

sublethal body burden of CPY in the adult bees from other sources, such as pol-
len, nectar and water.

Honey bees actively forage for water to regulate temperature of the hive through
evaporative cooling, to prepare larval brood food, and for their own metabolism
(Gary 1975 ; Winston 1987 ). Exposure of pollinators from large CPY contaminated
bodies of water is probably insignificant since bees do not collect water from large
areas of open water. The main water sources for bees are wet foliage, dew, and