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Environmental fate & pathways

Additional information on environmental fate and behaviour

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Administrative data

Endpoint:
additional information on environmental fate and behaviour
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Non-GLP, no available guideline, ancient study but of relevance for BPT assessment and ozone hazard classification.

Data source

Reference
Reference Type:
study report
Title:
Unnamed
Year:
1989
Report Date:
1989

Materials and methods

Test guideline
Qualifier:
no guideline available
GLP compliance:
no
Remarks:
prior to GLP
Type of study / information:
Reaction with ozone, atmospheric degradation kinetics

Test material

Reference
Name:
Unnamed
Type:
Constituent
Details on test material:
purity: propellant grade (Olin) analyzed according to MIL-P-27404B. purity stated only in second run of experiments (minimized wall reactions): >98.7%, <1.5% water

Results and discussion

Any other information on results incl. tables

First experiments:

In 6515-liter fluorocarbon-film environmental chamber, MMH disappeared (t1/2 = 19 h) from the environmental chamber but the loss was due to the physical interactions of adsorption onto and permeation through the fluorocarbon walls rather than by chemical oxidation. In pure nitrogen, the rate of disappearance was the same as in air. If any oxidation occurred in pure air, the rate of oxidation was too slow to measure by this technique.

Adding metallic wall-materials, such as aluminum, galvanized steel, stainless steel, titanium, or corroded aluminum, to the chamber increased the rate of disappearance (catalized). With corroded aluminum surfaces, a rapid surface-catalyzed air-oxidation reaction occurred. The relative activities of oxide-coated metal surfaces for the oxidation of MMH in air is: Fe > A1203 > Zn > 316 SS > Ti > Cr > Al > 304-L SS > Ni

The products of MMH oxidation are methane, methanol, methyldiazene (thermally unstable), and in several cases, traces of ammonia.

Second experiments to minimize wall reactions:

The ozonation of MMH occurred by a delayed branching-chain mechanism and was biphasic. The ozone concentration also varies from as little as 0.02 ppm v/v in rural areas to as much as 0.5 ppm in heavily polluted urban atmospheres; degradation initiation (limiting phase: first phase) half-lives at 12 -37°C were calculated to range 0.75 -3 hours at 0.15 ppm O3 and 2.5 -9 hours at 0.05 ppm. The half-life of MMH in a moderately polluted daytime atmosphere containing ozone, hydrocarbons, and nitrogen oxides is less than two hours, due to their reactions with ozone and hydroxyl radicals. The impact of the hydrazines may be manifested primarily by their effect of increasing the hydroxyl/hydroperoxyl radical concentrations in the atmosphere.

The products of ozonation were formaldehyde, methyldiazene, diazomethane, methanol, hydrogen peroxide, water, and possibly CO2. The nitrogenous compounds would ultimately yield nitrogen.

In a daytime atmosphere, hydroxyl and hydroperoxyl radicals formed from the ozonization of the hydrazines can cause a cycle of reactions that involve: the oxidation of nitric oxide to nitrogen dioxide; the photolysis of nitrogen dioxide to nitric oxide and oxygen atoms; and the combination of oxygen atoms with dioxygen to form ozone. The net result is an increase in ozone.

Applicant's summary and conclusion

Conclusions:
In atmosphere, oxidative or ozonation degradation of MMH in various realistic environmental conditions (temperature, ozone) is quick with t1/2 of less than one hour to at most 9 hours.
No hazard to ozone layer is anticipated (non-halogenated compound, reactions include consumption and later restauration of ozone).
Executive summary:

Atmospheric degradation of MMH in artificial spaces is efficiently catalyzed by coating of internal metal surfaces (especially Fe, Al2O3, Zn) so that oxidation by air becomes negligible. If any oxidation occurred in pure air, the rate of oxidation was too slow to measure by this technique.

In a moderately polluted daytime atmosphere containing ozone, hydrocarbons, and nitrogen oxides is less than two hours, due to their reactions with ozone and hydroxyl radicals. A balancing factor is the efficiency of the adsorption process, surface-catalyzed air-oxidation process, or both, that may also take place on hydrophilic airborne particulate matter. These surface interactions generally do not result in the desorption of reactive intermediates and represent an relatively innocuous pathway for the removal of atmospheric MMH. The radicals formed, themselves, lead to restauration of ozone.

MMH degradation products by oxidation or ozonation included methane, methanol, formaldehyde, diazomethane, methyldiazene (thermally unstable), hydrogen peroxide, water, traces of ammonia and possibly CO2; nitrogen is a terminal product of nitrogenous compounds.