| Environmental Fate | TERRESTRIAL FATE: The major degradation process for malononitrile in moist soil
may be hydrolysis. At 25 deg C, the aqueous hydrolysis half-life has been experimentally
determined to vary from 21.4 days at pH 5 to 3.1 days at pH 9(1,SRC). Insufficient data are
available to predict the importance of biodegradation. One microbial screening study has
demonstrated that malononitrile can be toxic to activated sludge microorganisms at a relatively
high conc of 500 mg/L . Based upon an estimated Koc value of 6.6, malononitrile should leach
readily in soil(3,SRC); the importance of leaching may be lessened, however, by concurrent
hydrolysis.
AQUATIC FATE: The major degradation process for malononitrile in water may be hydrolysis.
At 25 deg C, the hydrolysis half-life has been experimentally determined to vary from 21.4 days at
pH 5 to 3.1 days at pH 9(1,SRC). Insufficient data are available to predict the importance of
biodegradation. One microbial screening study has demonstrated that malononitrile can be toxic
to activated sludge microorganisms at a relatively high conc of 500 mg/L . Aquatic
volatilization, bioconcentration, direct photolysis, and adsorption to sediment are not expected to
be environmentally important.
ATMOSPHERIC FATE: Using measured vapor pressures of 11 mm Hg at 99 deg C and 20 mm
Hg at 109 deg C , the vapor pressure of malononitrile can be extrapolated to 0.015 mm Hg at
25 deg C using the Antoine relationship. Based upon this vapor pressure, malononitrile is
expected to exist primarily in the vapor-phase in the ambient atmosphere(2,SRC). It is expected
to degrade very slowly in an average ambient atmosphere by reaction with photochemically
produced hydroxyl radicals with an estimated half-life of about 2.67 yr(3,SRC). Due to its high
water solubility, malononitrile should be susceptible to wet deposition processes such as physical
removal via rainfall. The half-life for the aqueous hydrolysis of malononitrile at 25 deg C in acidic
to neutral conditions is about 20-21 days(4,SRC).
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