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Environmental fate & pathways

Phototransformation in water

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Description of key information

Data have been obtained from secondary source.
Based on an estimated average singlet oxygen concentration of 4x10-14molar in typical eutrophic fresh water and the experimental reaction rate constant, this reaction still would not be important in water (half-life of ≈500 days) (of Tratnyek et al. 1991).

Key value for chemical safety assessment

Half-life in water:
500 d

Additional information

Photoreduction in water: 2,4-DNP may be photoreduced to 2-amino-4-nitrophenol in the presence of ascorbic acid or ferrous ions, and the reaction is sensitised by chlorophyll. The possibility of such photoreduction exists in natural water in which the suspended reducing matter may act as a reducing agent and humic substances or algae may serve as a sensitizer (Massini P, Voorn G. 1967).

Reaction with singlet oxygen (O2) and peroxy radicals (RO2): the estimated rate constants for the reaction of 2,4-DNP with singlet oxygen (O2) and peroxy radicals (RO2) are 3x10^4molar-hour and 5x10^5/molar-hour, respectively (Mabey WR, Smith JH, Podoll RT, et al. 1981).

Based on an assumption that the concentrations of singlet oxygen and peroxy radicals in typical eutrophic waters are 10^-12 and 10^-9 molar, respectively (Mill and Mabey 1985) the reaction of hydroperoxy radicals (HO2) with 2,4-DNP that produces a ring hydroxylated product would not be significant (classical Fenton reaction). Hence, the direct photolysis of 2,4-DNP in water is too slow to be an important environmental fate process (Lipczynska-Kochany E, 1991).

Another experimental value for the rate constant for 2,4-DNP’s reaction with singlet oxygen is 4.05x10^5molar-second.

Half-life: based on an estimated average singlet oxygen concentration of 4x10^-14 molar in typical eutrophic fresh water and the experimental reaction rate constant, this reaction still would not be important in water (half-life of ≈500 days) (Tratnyek et al. 1991)