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EC number: 200-835-2
CAS number: 75-05-8
Acetonitrile is a volatile liquid
with a vapour pressure of 9,864 Pa at 25ºC and rapid volatilization to
the atmosphere is expected when acetonitrile is released to the
Henry's Law constants have been reported for acetonitrile ranging from
2.07 - 3.5 Pa-m3/mole (Snider and Dawson, 1985; Hine and Mookerjee,
1975; Gaffney, 1987 as cited in HSDB, 2009). These values indicate that
volatilization of acetonitrile from surface waters and moist soils is
likely to be significant (Howard, 1993).
US EPA HENRYWIN software (v3.10) calculated a Henry's Law Constant of
7.902E-5 atm-m3/mole (8.0 Pa-m3/mole) for acetonitrile based on vapor
pressure of 200 mmHg and water solubility of 1.37E5 mg/L. Based on this
value, volatilization half-lives for a model river and model lake were
estimated to be 18 hours and 7 days, respectively.
The removal of acetonitrile from
the atmosphere by precipitation has been quoted in several reports as
one of the main fate processes for this compound, as important as the
photo-oxidation reaction with hydroxyl radicals (Hamm et al., 1989; Hamm
and Warneck, 1990). A residence time of about 3 years has been estimated
for acetonitrile in the troposphere due to wet deposition (Hamm et al.,
1984; Arijs and Brasseuur, 1986).
An overall residence time for
acetonitrile near 1.5 years was calculated considering the two principal
removal processes, precipitation and reaction with hydroxyl radicals
(Hamm and Warneck, 1990; Arijs and Brasseur, 1986). However, a shorter
residence time was calculated based on the tropospheric mass balance of
this compound (Hamm and Warneck, 1990). They estimated a mass content
(G) in the troposphere of 370-570 x 103tonnes acetonitrile
and a global source strength (Q) of 600-1,100 x 103tonnes
acetonitrile / year, which would yield an overall residence time,
calculated as G/Q, of 0.23-0.95 years. The dissolution in the ocean was
proposed as an effective process for acetonitrile removal, that would
take up 65% of the total acetonitrile emission, and the combined
residence time for the process (precipitation, hydroxyl radical reaction
and ocean dissolution) was estimated to be of 0.45 years, which is in
agreement with the mass balance estimate.
The adsorption coefficient, Koc,
can be estimated for acetonitrile using the octanol-water partition
coefficient, log Pow= -0.34 (Leo et al., 1971), and Kocvalues
of 0.3-16 l/kg were obtained using regression equations reported in
Lyman et al (1982).EPA PCKOC software (v1.66) generated an
estimated Koc of 4.5 for acetonitrile.These
Kocvalues indicate a low potential for adsorption to soils;
given the high water solubility of acetonitrile leaching to groundwater
may be important when spilled on soil (Howard, 1993).
US EPA EPIWIN software (v3.20) Level III Fugacity Model predicted the
following percent distribution and half-lives for acetonitrile in
Air - 13%, 1544 hours
Water - 44.1%, 360 hours
Soil - 42.8%, 720 hours
Sediment - 0.0811%, 3240 hours
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