Fumigants
137
TABLE 8.4
Models for Translating Emissions into Ambient Concentrations in Comparison to
the Risk-Based Reference Concentration
Ambient Concentrations of MeBr in the Salinas Valley, CA (µg/m 3 )
Salinas North Salinas South Arroyo Seco King City
Highest 24 hour Avg. Conc.
5.68
5.94
1.65
0.51
Measured
Annual Time Wt. Avg. Conc.
2.48
2.51
0.76
0.29
(WAC)
Worst Case
4.96
5.02
1.52
0.58
(ISCST3) = 2 × WAC
Worst Case
4.12
4.17
1.26
0.48
(CALPUFF) = 1.66 × WAC
NOAEL= 81,600 kg/m 3
LOAEL (HEC) = 480 µg/m 3
Source: Reprinted from Honaganahalli, P.S., and Seiber, J.N. (2000). Measured and predicted
airshed concentrations of methyl bromide in an agricultural valley and applications to
exposure assessment. Atmos. Environ. 34, 3511–3523. Copyright (2000), with permission
from Elsevier.
Note: These are worst case ambient air concentrations for comparison with NOAEL (Lim,
1992) and lowest-observed-adverse-effect level (LOAEL) values (IRIS, 1992) from CalEPA
Offce of Environmental Health Hazard Assessment (OEHHA). Choosing the more conservative models provided an additional margin of safety.
Section 8.3.2 was adapted and partially (Reprinted from Atmospheric
Environment 34, Honaganahalli, P.S., and Seiber, J.N., Measured and predicted airshed concentrations of methyl bromide in an agricultural valley
and applications to exposure assessment, Pages 3511–3523, Copyright (2000),
with permission from Elsevier.)
8.4 Modeling Emissions
Table 8.5 contrasts emission rates measured immediately after application
for fve different fumigants with different vapor pressures (VPs) and soil
mobilities: chloropicrin, 1,3-D, MITC, methyl iodide (MeI), and MeBr with
different application methods and depths (Woodrow et al., 2011). Emission
rates of fumigants depend on their VP and soil diffusion rates (S w ); however, the same fumigant emits at different rates based on application method
(see MITC drip, shank, surface chemical application), and the depth (see MeI,
injected at three depths).
Numeric techniques that correlate pesticide physicochemical properties
with empirically determined emissions such as these values can be used to
estimate emission rates for different fumigants and different conditions of
137
TABLE 8.4
Models for Translating Emissions into Ambient Concentrations in Comparison to
the Risk-Based Reference Concentration
Ambient Concentrations of MeBr in the Salinas Valley, CA (µg/m 3 )
Salinas North Salinas South Arroyo Seco King City
Highest 24 hour Avg. Conc.
5.68
5.94
1.65
0.51
Measured
Annual Time Wt. Avg. Conc.
2.48
2.51
0.76
0.29
(WAC)
Worst Case
4.96
5.02
1.52
0.58
(ISCST3) = 2 × WAC
Worst Case
4.12
4.17
1.26
0.48
(CALPUFF) = 1.66 × WAC
NOAEL= 81,600 kg/m 3
LOAEL (HEC) = 480 µg/m 3
Source: Reprinted from Honaganahalli, P.S., and Seiber, J.N. (2000). Measured and predicted
airshed concentrations of methyl bromide in an agricultural valley and applications to
exposure assessment. Atmos. Environ. 34, 3511–3523. Copyright (2000), with permission
from Elsevier.
Note: These are worst case ambient air concentrations for comparison with NOAEL (Lim,
1992) and lowest-observed-adverse-effect level (LOAEL) values (IRIS, 1992) from CalEPA
Offce of Environmental Health Hazard Assessment (OEHHA). Choosing the more conservative models provided an additional margin of safety.
Section 8.3.2 was adapted and partially (Reprinted from Atmospheric
Environment 34, Honaganahalli, P.S., and Seiber, J.N., Measured and predicted airshed concentrations of methyl bromide in an agricultural valley
and applications to exposure assessment, Pages 3511–3523, Copyright (2000),
with permission from Elsevier.)
8.4 Modeling Emissions
Table 8.5 contrasts emission rates measured immediately after application
for fve different fumigants with different vapor pressures (VPs) and soil
mobilities: chloropicrin, 1,3-D, MITC, methyl iodide (MeI), and MeBr with
different application methods and depths (Woodrow et al., 2011). Emission
rates of fumigants depend on their VP and soil diffusion rates (S w ); however, the same fumigant emits at different rates based on application method
(see MITC drip, shank, surface chemical application), and the depth (see MeI,
injected at three depths).
Numeric techniques that correlate pesticide physicochemical properties
with empirically determined emissions such as these values can be used to
estimate emission rates for different fumigants and different conditions of