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Description of key information

Photodegradation in air:  Half-life in air: 10.7 d. Degradation rate constant with OH radicals: 1.5 x 10-12 cm³ molecule-1 s-1

Key value for chemical safety assessment

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

Additional information

The SRC AOPWIN program (v1.92) has been used to obtain values of the rate constantkOHfor reaction of M3T with hydroxyl radicals. This prediction method has not been validated to assess applicability to siloxanes; therefore, there is uncertainty associated with the calculated values obtained.

The overall half-life in air under default conditions of hydroxyl radical concentration was calculated using the following expressions:

kdegair(d-1) = kOH(cm3/molecule.sec) x OH Concair(molecules/cm3) x 24 x 3600

DT50(d) = ln 2/ kdegair(d-1)

Where:

kdegair= total rate constant for degradation in air

kOH= rate constant for reaction with hydroxyl radicals

OH Concair= concentration of hydroxyl radicals in air = 5 x 105OH molecules/ cm3

DT50= half-life

The concentration of hydroxyl radicals in air of 5 x 105OH molecules/ cm3, and the 24 hour photoperiod, are the values specified in the Technical Guidance Document (EC, 2003a).

The results are given in Table 4.1.2.

Table4.1.2Results of photodegradation in air calculations

Parameter

Result, M3T

kOH (cm3/ molecule.sec)

1.5 x 10-12

kdegair (d-1)

0.06

DT50(days)

10.7