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Environmental fate & pathways

Phototransformation in air

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Reference
Endpoint:
phototransformation in air
Type of information:
experimental study
Adequacy of study:
key study
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
other: Basic data are given.
Principles of method if other than guideline:
The OH concentration was monitored as a function of time comparing the behaviour in the absence and presence of the test substance
GLP compliance:
not specified
Details on test conditions:
Sensitiser (for indirect photolysis): OH
Sensitiser concentration: smaller or equal than 1*E11 molecule/cm³
DT50:
6.3 h
Test condition:
OH concentration of 500000 molecules/cm³; rate constant 6.1 E-11 cm³/(molecule * s) (T= 298 - 424 K)

- rate constants at different temperatures were reported as well:

298 K: 6.5*E11 cm³/(molecule * s)

355 K: 5.9*E11 cm³/(molecule * s)

424 K: 5.8*E11 cm³/(molecule * s)

Executive summary:

Hydrazine is rapidly degraded under the presence of hydroxyl radicals yielding a temperature independent rate constante of 6.1 E-11 cm³/(molecule * s) (T= 298 - 424 K) (Pitts et al., 1980). Based on these results an atmospheric half life of 6.3 h can be calculated assuming an OH concentration of 500000 molecules/cm³.

Description of key information

Hydrazine is rapidly degraded under the presence of hydroxyl radicals yielding a temperature independent rate constant of 6.1 E-11 cm³/(molecule * s) (T= 298 - 424 K) (Pitts et al., 1980). An atmospheric half life of 6.3 h can be calculated based on the derived rate constant and an assumed OH concentration of 500000 molecules/cm³ indicating only a limited potential for a long range atmospheric transport.

Key value for chemical safety assessment

Half-life in air:
6.3 h
Degradation rate constant with OH radicals:
0 cm³ molecule-1 s-1

Additional information

According to the guidance document R.11 (ECHA, 2008, p19), substances with an atmospheric half-life < 2 days are not expected to stay in the atmosphere for long as they will degrade rapidly. Concludingly, there will be a limited potential for long range atmospheric transport when discussing the behaviour of hydrazine.