Environmental Fate and Transport of Solvent-Stabilizer Compounds - Environmental Investigation and Remediation - page 126

TABLE 3.5
Calculated and Experimental Atmospheric Half-Lives of Stabilizer Compounds

Photo-Oxidation in Presence
of 5 ppm NO Photo-Oxidation

Compound t 1/2 Reference t 1/2 Reference

n -Methyl pyrrole 0.4 h 1 —

2,2,4-Trimethyl pentene-1 1.6 h 1 —

Cyclohexene 2.3 h 1 —

Triethanolamine - 4 h 2

sec -Butyl alcohol 17 h 1 —

1,4-Dioxane 8.8 h 1 22.4 h 3

1-2 days 4

Nitromethane 24 h 1 100 days 5

1,3-Dioxolane — 26.5 h 6

Cyclohexane 18 h 1 45 h 7, 8

tert -Amyl alcohol — 3.3 days 7, 9

1,2-Butylene oxide — 8.4 days 9

tert -Butyl alcohol 90 h 1 14 days 9

Epichlorohydrin 42 h 1 45 days 9

Nitroethane — 107 days 9

Sources: [1] Dilling et al. (1976); [2] Dow Chemical (1980); [3] Maurer et al. (1999); [4] Platz et al. (1997); [5] Nielsen
et al. (1989); [6] Buxton et al. (1988); [7] Bidleman (1988); [8] Chao et al. (1983); and [9] Meylan and Howard
(1993).
Notes: Values cited in the literature from the Dilling et al. (1976) study often mistakenly cite the 1,4-dioxane half-life as
3.4 h. The Dilling study used light intensity much higher than sunlight; measured half-lives are multiplied by 2.6 to
estimate the half-life under bright sunlight conditions. Values from the Dilling study were measured in the presence
of 5 ppm of nitrous oxide (NO); therefore, photo-oxidation is likely the dominant process for values from Dilling
et al.

wet deposition of soluble airborne contaminants at night, leading to a low-concentration distribution
to surface water and groundwater. Rain also washes out soluble and particulate airborne contami-
nants. Numerous studies have been conducted to elicit the photo-oxidation pathway for 1,4-dioxane
(Maurino et al., 1997; Platz et al., 1997; Geiger et al., 1999; Li and Pirasteh, 2006). The pathway by
which 1,4-dioxane reacts with hydroxyl radicals is summarized in Figure 3.2 .
In the photo-oxidation pathway for 1,4-dioxane (mapped in Figure 3.2), one of the eight hydrogen
atoms on the 1,4-dioxane molecule [A] reacts with OH • followed by addition of oxygen to form a
1,4-dioxyl radical [B]. The dioxyl radical in turn converts NO to NO 2 , producing an alkoxyl radical
[C]. The alkoxyl radical is rapidly converted to the HC(O)O(CH 2 ) 2 OCH 2 radical [D] via a very fast
ring-opening reaction. Addition of oxygen forms another peroxyl radical HC(O)O(CH 2 ) 2 OCH 2 O 2
[E]. This peroxyl radical will convert NO to NO 2 , forming HC(O)O(CH 2 ) 2 OCH 2 O [F], which reacts
with molecular oxygen to produce ethylene-1,2-diformate (EDF—also called ethylene glycol difor-
mate) [G]. EDF will degrade from successive reactions with hydroxyl radicals, as delineated by
Maurer et al. (1999).
Atmospheric oxidation of 1,4-dioxane in the presence of nitrogen oxide (NO) produces EDF with
an approximately 100% molar yield. If the annual average tropospheric OH • concentration of 1 × 10 6
molecules per cubic centimeter is used, the total residence times of 1,4-dioxane and EDF in the
atmosphere will be 22.4 h and 24 days, respectively. EDF can therefore be expected to travel far
from its source; however, because EDF is highly soluble in water, removal by wet precipitation or
“rain-out” will shorten its atmospheric lifetime in wet climatic regions (Maurer et al., 1999).