34
Pesticides, Organic Contaminants, and Pathogens in Air
TABLE 3.2
Volatilization Rates for Pesticides Applied to Water
Ln
Absolute Flux
Water Conc.
Compounds
(VP/Sw)
(µg/m 2 ·hr)
(mg/L)
Ln (fux/[mg/L])
Deltamethrin
−6.91
1.3–3.5
0.00034–0.00095
8.23
Deltamethrin
−6.91
1.3–6.4
0.00034–0.00173
8.23
Diazinon
−8.94
4.8 × 10 3
13.5
5.87
Eptam
−4.42
2.6 × 10 4
2.17
9.39
Ethyl-parathion
−9.98
605
3.5
5.15
Me-parathion
−10.3
1.12 × 10 3
14.5
4.35
Mevinphos
−14.53
399
174
0.83
Molinate
−6.83
5.75 × 10 3
3.43
7.42
Molinate
−6.83
3.93 × 10 3
1.80
7.69
Molinate
−7.57
1.58 × 10 4
25.1
6.44
Thiobencarb
−9.62
160
0.57
5.64
Thiobencarb
−9.62
3.88 × 10 3
16.3
5.47
Source: Reprinted (adapted) with permission from Woodrow, J.E., Seiber, J.N., and Baker, L.W.
(1997). Correlation Techniques for Estimating Pesticide Volatilization Flux and Downwind
Concentrations. Environ. Sci. Technol. 21(2), 523–529. Copyright (1997) American Chemical
Society.
y = 13.643 + 0.8687x, r
2 = 0.970
(3.9)
where y = Ln (fux/[mg/L]) and x = Ln (VP/Sw). This correlation was especially encouraging in view of the fact that the database contained a mix of
laboratory and feld volatilization measurements. While a good correlation
of the data required normalizing fux to water concentration, it is the absolute fux values (µg/m 2 ·hr) that give a true measure of the mass movement of
chemical from water to air. For example, since the water solubility of deltamethrin is so exceedingly low (Sw = 0.002 mg/L), the concentration in water
will also be low in feld situations, and the absolute fux of this compound
would not be expected to be very high on just a mass/area basis, even though
normalized fux placed deltamethrin near eptam (Sw = 375 mg/L). This is
borne out by the absolute fux values measured in the feld for deltamethrin
(1.3–6.4 µg/m 2 ·hr) and eptam (2.6 × 10 4 µg/m 2 ·hr). The correlation should be
used to derive absolute fux values from chemical properties and measured
water concentrations. Field measurements of fux were accomplished using
techniques discussed in Section 3.2.4.
So, the volatilization fux of a water-borne chemical depends on both vapor
pressure and water solubility. A nonpesticide example is the Deepwater
Horizon oil rig blowout in April 2010 that resulted in a 5-month outfow of
crude oil from the ocean foor before it was capped. The lighter hydrocarbons in the water column volatilized rapidly after the spill because of their
Pesticides, Organic Contaminants, and Pathogens in Air
TABLE 3.2
Volatilization Rates for Pesticides Applied to Water
Ln
Absolute Flux
Water Conc.
Compounds
(VP/Sw)
(µg/m 2 ·hr)
(mg/L)
Ln (fux/[mg/L])
Deltamethrin
−6.91
1.3–3.5
0.00034–0.00095
8.23
Deltamethrin
−6.91
1.3–6.4
0.00034–0.00173
8.23
Diazinon
−8.94
4.8 × 10 3
13.5
5.87
Eptam
−4.42
2.6 × 10 4
2.17
9.39
Ethyl-parathion
−9.98
605
3.5
5.15
Me-parathion
−10.3
1.12 × 10 3
14.5
4.35
Mevinphos
−14.53
399
174
0.83
Molinate
−6.83
5.75 × 10 3
3.43
7.42
Molinate
−6.83
3.93 × 10 3
1.80
7.69
Molinate
−7.57
1.58 × 10 4
25.1
6.44
Thiobencarb
−9.62
160
0.57
5.64
Thiobencarb
−9.62
3.88 × 10 3
16.3
5.47
Source: Reprinted (adapted) with permission from Woodrow, J.E., Seiber, J.N., and Baker, L.W.
(1997). Correlation Techniques for Estimating Pesticide Volatilization Flux and Downwind
Concentrations. Environ. Sci. Technol. 21(2), 523–529. Copyright (1997) American Chemical
Society.
y = 13.643 + 0.8687x, r
2 = 0.970
(3.9)
where y = Ln (fux/[mg/L]) and x = Ln (VP/Sw). This correlation was especially encouraging in view of the fact that the database contained a mix of
laboratory and feld volatilization measurements. While a good correlation
of the data required normalizing fux to water concentration, it is the absolute fux values (µg/m 2 ·hr) that give a true measure of the mass movement of
chemical from water to air. For example, since the water solubility of deltamethrin is so exceedingly low (Sw = 0.002 mg/L), the concentration in water
will also be low in feld situations, and the absolute fux of this compound
would not be expected to be very high on just a mass/area basis, even though
normalized fux placed deltamethrin near eptam (Sw = 375 mg/L). This is
borne out by the absolute fux values measured in the feld for deltamethrin
(1.3–6.4 µg/m 2 ·hr) and eptam (2.6 × 10 4 µg/m 2 ·hr). The correlation should be
used to derive absolute fux values from chemical properties and measured
water concentrations. Field measurements of fux were accomplished using
techniques discussed in Section 3.2.4.
So, the volatilization fux of a water-borne chemical depends on both vapor
pressure and water solubility. A nonpesticide example is the Deepwater
Horizon oil rig blowout in April 2010 that resulted in a 5-month outfow of
crude oil from the ocean foor before it was capped. The lighter hydrocarbons in the water column volatilized rapidly after the spill because of their