Risk to Pollinators from the Use of Chlorpyrifos in the United States - Reviews of Environmental Contamination and Toxicology - page 235

Although much has been written on communities of pollinators in agricultural land-
scapes and factors that influence diversity and abundance of bee populations in these
habitats (Williams et al. 2010 ; Winfree et al. 2009 ), there is limited information on
nesting habits of ground nesting bees within cropping systems (Julier and Roulston
2009 ; Kim et al. 2006 ; Williams et al. 2010 ; Wuellner 1999 ), and on exposure of
ground nesting bees to pesticides. The potential use of data from surrogate species
was therefore considered.
The exposure of arthropods to CPY in soil following application of spray or
granular formulations on the soil surface has been studied, mainly for characterizing
exposure in birds that consume insects (Moore et al. 2014 ; Solomon et al. 2001 ).
Fewer studies have examined exposure of arthropods to CPY in soil, and these were
done to evaluate the efficacy of CPY against pest insects (Clements and Bale 1988 ;
Tashiro and Kuhr 1978 ; Tashiro 1987 ). None of these studies included pollinators.
Exposures are different for ground-burrowing insect pests that ingest contaminated
vegetation or soil, making these data unsuitable for estimating exposures of ground-
nesting pollinators. Thus, exposures of soil-dwelling pollinators via this route were
not estimated and it remains an area of uncertainty.
Exposure via drinking - water . Water is potentially a significant route of exposure
(Fig. 1 ). In obtaining water for a large number of individuals in a colony, honey bees
collect much more water than other bees, and therefore serve as a conservative rep-
resentative species for this route of exposure. Typical sources include wet foliage,
puddles, soil saturated with water, or other sources where they can get access to
water without drowning (Gary 1975 ; Winston 1987 ). Because CPY is not systemic,
exposure to CPY through guttation water is not significant (Fig. 1 ).
Only a small proportion of the honey bees in a hive are dedicated to foraging for
water and recruiting other bees to forage for water (Winston 1987 ). Water contain-
ing CPY brought back to the hive is limited to sublethal levels low enough that the
ability of the forager to return to the hive is not affected. When demand for water is
large, foraging can continue through the day. Individual loads of water average
approximately 25 mg although some loads can be larger, and each load can take
approximately 10-12 min to obtain and deliver into the hive. If foraging continues
for 10 h, the forager would carry 50 loads or 1,250 mg of water to the hive (Gary
1975 ) from a source such as a puddle. Honey bees do not forage during rain and the
overlap of foraging time with the time when soil is wet enough for bees to collect
soil pore water is short. Exposure from puddles is recommended to represent the
worst case for collection of water from the soil surface (USEPA 2012 ).
The time when water can be obtained from wet foliage is also short. It takes
approximately 1 h for wet foliage to dry. Foraging after the dew point is reached in
the evening is unlikely, but more than one rain event is possible. If water is collected
from wet foliage for 2 h each day the forager can carry as much as 250 mg of water
from that source. Temperature is lower and humidity is greater when the foliage is
wet, and this reduces demand for water in the hive, making this an upper-limit
estimate.
The amount of water a honey bee will actually drink is unknown (USEPA 2012 )
and likely variable. An estimated rate of intake of 47 μL d −1 based on direct