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Environmental fate & pathways

Phototransformation in air

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Description of key information

The half-life of 4-aminophenol and its degradation rate constant in the presence of hydroxyl radicals were predicted by the use of quantitative structural activity relationship modeling, by the use of AOPWIN v1.92a, a model within the EPI Suite v4.00, validated QSAR model, part of OECD (Q)SAR Toolbox.

Key value for chemical safety assessment

Half-life in air:
1.729 h

Additional information

The photolysis half-life and degradation rate constant of 4-aminophenol were estimated, based on QSAR modeling. The degradation constant with hydroxyl radicals was predicted to be74.2471 E-12cm3/molecule-1s-1. Assuming a hydroxyl radical concentration [-OH] of 1.5 x 106molecules/cm3and 12 hours of sunlight, the half-life was predicted as 1.729 hours (0.144 days).

The model User's Guide states that the 24-hour daylight average hydroxyl radical concentration may be more appropriate for chemicals that react more slowly (i. e.,> a few days). Since the modeling results indicate that 4-aminophenol is a fast-reacting chemical (with a half-life in the scale of hours), the estimated half-life associated with the default hydroxyl radical concentration with 12-hour daylight cycle (i. e., 1.729 hours) is considered the more appropriate of the two estimated half-life values.