Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 221

individual (e.g., a foraging worker), or secondary if other adults or offspring in a
hive or nest are subsequently exposed. Potential exposures through various com-
partments of air, water, soil, and vegetation are complex and interconnected. The
pathway of exposure via water was divided into precipitation, surface water, rain
and dew on leaves, and guttation. The vegetation component was comprised of foli-
age, pollen, honeydew, and nectar.
Although other pollinators were considered to the extent possible based on avail-
able literature, honey bees were the main focus of this risk assessment. Honey bees
are the major pollinators of crops in North America, and are the subject of well-
developed standardized methods for evaluating exposure and effects as compared to
non- Apis bees. They are considered a useful surrogate for other pollinators, particu-
larly in regulatory risk assessment. Because they forage on a wide variety of plant
hosts, have a tendency to focus on specific pollen or nectar sources for extended
periods, and have a greater foraging range compared with other pollinators, expo-
sures of honey bees are widely used as a worst-case exposure scenario among pol-
linators (Porrini et al. 2003 ).
Non- Apis bee pollinators can be exposed to CPY in ways that are different from
those for honey bees (Fig. 1 ). Most non- Apis bees are solitary nesters and use soil
and/or vegetation in the construction of nests (e.g., Megachile , Osmia ), or nest in
soil (e.g., Andrenidae, Halictidae) (Michener 2007 ). The significance of these alter-
native routes of exposure should be taken into consideration when comparing the
potential for exposure. Since most pollinators are not predators, the route of expo-
sure via prey is considered incomplete (Fig. 1 ). Predators such as wasps ( Vespa sp.)
were excluded from the risk assessment. They are not major pollinators, fit better
into a conceptual model for higher trophic levels, and would be protected if the
major pollinators are not at risk.
The major potential routes of exposure are shown in the conceptual model in
Fig. 1 . The thickness of the arrows in the model approximates the relative impor-
tance of each pathway. The conceptual model shows the pathways for distribution
of applied material during and after application into the environmental compart-
ments that may lead to exposure of pollinators to CPY. Degradation and dissipation
occur in all compartments and there can be some redistribution of material between
compartments.
Primary routes of exposure . As mentioned above, labels for sprayable products con-
taining CPY caution against application on blooming crops or drift onto weeds or
surface water when bees are actively foraging. By eliminating direct contact with
airborne spray droplets or contact with spray liquid on surfaces before it dries, these
restrictions represent a major reduction in potential for primary exposure of pollina-
tors, both in the treated area and in the downwind areas where spray drift might
occur. Exposure to CPY vapor is insignificant due to the low vapor pressure
(Solomon et al. 2014 ), and CPY has no appreciable vapor action. The pathways for
direct exposure of pollinators to airborne spray droplets or vapor are therefore
shown as minor pathways in Fig. 1 .
For granular CPY products, there should be little or no exposure via drift of dust,
or deposition on foliage, pollen, or other surfaces. Chlorpyrifos is non-systemic and