Environmental Engineering Reference
In-Depth Information
measurements of water flux rates of the brown paper wasp (a similar species) is
considered reliable by the USEPA for regulatory purposes (USEPA
2012
). To sim-
plify the risk assessment, it was assumed that bees collect their full daily require-
ment from the source with the highest concentration of CPY.
To estimate potential exposure of pollinators to CPY in water, it is also necessary
to know or estimate the concentration of CPY in different water sources, which are
expected to vary, and the amount of water pollinators derive from each potential
source. The main potential sources are evaluated below:
Puddles and soil pore water
. Several estimates of the concentration in puddles in the
field are available. The USEPA recommends that concentrations of pesticides in
puddles located on pesticide-treated fields be estimated using a modified version of
the Tier-1 rice model (v. 1.0) (USEPA
2012
). The model uses equilibrium partition-
ing to provide conservative estimates of environmental concentrations and assumes
that puddles can be directly sprayed with pesticide and the pesticide will instanta-
neously partition between a water phase and a sediment phase, independent of the
size of the puddle. With this model, the concentration is determined by partition
equilibrium and does not increase as the puddle dries out; residues are deposited on
the soil during drying to maintain the equilibrium. A sensitivity analysis was done
to identify parameters that would give high-end estimates of exposure, and peak
estimated concentrations are based on an application rate of 1.12 kg ha
−1
. The model
is represented in equation 1 (USEPA
2012
).
m
dd k
(1)
C
=
CPY
(
)
w
+
qr
+
w
sed
sed
b d
Where:
C
w
is the concentration in water (μg L
−1
),
m
CPY
is mass applied per unit
area (kg ha
−1
),
k
d
is water-soil partition coefficient (L kg
−1
) (equivalent to
K
OC
*0.01),
d
sed
is sediment depth,
dw
is water depth,
ρ
b
is bulk density (kg m
−3
), and
θ
sed
is
porosity.
Using the mean
K
OC
value of 8216 for CPY (Solomon et al.
2014
), the estimated
concentration in puddle-water in a field following a spray application of 1.12 kg
CPY ha
−1
is 0.0051 μg CPY L
−1
. Assuming that the intake rate of water is 47 μL d
−1
and that bees obtain 100% of their drinking water from such puddles on treated
fields, the Tier-1 estimate for CPY dose was 2.40 × 10
−7
μg CPY bee
−1
. For honey
bees collecting 1,250 μL d
−1
the estimated dose was 6.38 × 10
−6
μg CPY bee
−1
d
−1
.
The maximum concentration of CPY in puddles after application of both the
granular formulations and the sprayable formulations was also modeled using
PRZM/EXAMS, which provides both puddle and soil pore water concentrations
(Williams et al.
2014
). The maximum 95th centile of the peak pore water concentra-
tions from the PRZM/EXAMS model among registered uses in the U.S. of the gran-
ular and the spray formulations were 571 and 566 μg L
−1
, respectively, based on a
1.12 kg CPY ha
−1
application rate and the maximum number of applications per year.
These values were obtained from the North Carolina tobacco and California broc-
coli standard use scenarios for PRZM/EXAMS, respectively (Williams et al.
2014
).
The greatest peak concentrations predicted for puddle water were 285 μg L
−1
for
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