Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 228

richteri ), and European corn borer ( Ostrinia nubilalis ) larvae, 5.5, 25, and 30.7%
of CPY was excreted, respectively (Chambers et al. 1983 ; Tetreault 1985 ; Wass and
Branson 1970 ).

3.3 Tier-1 Characterizations of Exposure

Estimates of contact exposure during spray application . CPY is applied as an insec-
ticide and mitigation measures are required to protect pollinators. Such measures
are described on product labels. Bee-kill incidents in the U.S. involving direct expo-
sure to CPY are rare (see section on Incident Reports below), indicating that the
effectiveness and level of compliance with these measures are high. Therefore, the
direct contact route of exposure was not considered in the higher tier refinements of
the risk assessment.

Estimates of dietary exposure . The USEPA has proposed that doses of pesticide
received by bees via food can be calculated from rates of consumption of nectar and
pollen estimated for larval and adult worker bees (USEPA 2012 ). Because toxicity
data are expressed as doses (μg CPY bee −1 ), it is necessary to convert estimated
concentrations of CPY in food (mg CPY kg −1 ) into doses. For honey bee larvae, the
proposed total food consumption rate is 120 mg d −1 . For adult workers, a median
food consumption rate of 292 mg d −1 is proposed, based on nectar consumption
rates of nectar-foraging bees, which are expected to receive the greatest dietary
exposures among different types of worker bees (USEPA 2012 ). These values are
conservative estimates of dietary consumption and are expected to be protective of
drones and queens as well. These methods are additionally conservative in that they
assume that the pesticides do not degrade in the hive. The USEPA recommends that
this Tier-1 exposure assessment covers both honey bees and other non- Apis bees
(USEPA 2012 ).
Estimates of pesticide levels in nectar and pollen calculated by the T-REX model
have been proposed (USEPA 2012 ). Based on upper-bound residue values for tall
grass, 110 mg CPY kg −1 nectar for an application rate of 1.12 kg CPY ha −1 is pro-
posed as a conservative (high-end) estimate of dose received by bees consuming
nectar. An identical screening value of 110 mg CPY kg −1 pollen for an application
rate of 1.12 kg CPY ha −1 is proposed for pollen. These values assume that concen-
trations are distributed uniformly in the plant tissues. They are converted to an esti-
mated dietary dose that is based on larval and adult worker bees consuming
aforementioned rates of pollen and nectar (120 and 292 mg d −1 , respectively).
Therefore, the proposed dietary exposure values for larvae and adults are 12 μg
CPY bee −1 kg CPY ha −1 , and 29 μg CPY bee −1 kg CPY ha −1 , respectively (USEPA
2012 ). Using these high-end proposed dietary exposure rates with maximum (1.05-
6.31 kg CPY ha −1 ) and minimum (0.26-2.10 kg CPY ha −1 ) application rates for
Lorsban 4E and Lorsban Advanced, gives estimated CPY dietary exposure esti-
mates ranging from 3 to 183 μg CPY bee −1 , depending on application rate and life
stage (Table 1 ).