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Environmental fate & pathways

Phototransformation in air

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Description of key information

Data have been obtained from secondary source and HSDB databank.
The only availlable estimated rate constant for the reaction of vapour-phase from data of 2,4-DNP with hydroxyl radicals is 5.76x10-13cm3/molecule-second.
Based on an average ambient atmospheric concentration of hydroxyl radicals of 5x105radicals/cm3 the estimated half-life for the reaction is 28 days. Since dinitrophenols are expected to be present partly in the particulate phase in the air, the reaction rate is expected to be even slower than the estimated value for the gas phase reaction (Atkinson R. 1988).

Key value for chemical safety assessment

Half-life in air:
28 d

Additional information

The reactions of dinitrophenols with hydroxyl and nitrate radicals may be important in determining the residence times of dinitrophenols in the atmosphere. However, the products of these reactions have not been identified (Atkinson et al., 1992).

Estimation (SRC) indicates that 2,4-Dinitrophenol (2,4 -DNP) does absorb light at wavelengths >290 nm and therefore may be susceptible to direct photolysis by sunlight (Sadtler Res Lab).

For reaction with hydroxyl radicals two data estimated are available.

The first, using the Atkinson method estimates the rate constant for the reaction of vapor-phase 2,4-DNP with hydroxyl radicals at 5.76x10^-13cm3 molecule-second. Based on an average ambient atmospheric concentration of hydroxyl radicals of 5x10^5 radicals/cm3 the estimated half-life for the reaction is 28 days. Since dinitrophenols are expected to be present partly in the particulate phase in the air, the reaction rate is expected to be even slower than the estimated value for the gas phase reaction (Atkinson R. 1988).

Another SRC estimation sets the rate constant for the vapour-phase reaction of 2,4 -DNP with photochemically-produced hydroxyl radicals has been at 6.6X10^-13 cm3/molecule-sec at 25 °C using a structure estimation method SRC. This corresponds to an atmospheric half-life of about 24 day an atmospheric concentration of 5x10^ 5 hydroxyl radicals per cm3 (Meylan et al., 1993).

Reaction with nitrate radicals: the loss of dinitrophenols in the air due to this kind of chemical reactions should not be a significant environmental fate process (by structural analogy) (Grosjean D. 1985)