Methanaminium, N-[4-[[4-(dimethylamino)phenyl]phenylmethylene]-2,5-cyclohexadien-1-ylidene]-N-methyl-, ethanedioate

Phototransformation in water

Description of key information

t1/2, phototransformation in water, natural solar = 30h (8h irradiation/day)

total phototransformation, 210h, 25°C

Key value for chemical safety assessment

Half-life in water:

30 h

Additional information

Photolysis experiments (Perez et al, 2007) were performed by direct exposure of a solution of Malachite Green (MG) in water to natural sunlight. A phototransformation half-life was recorded at 30 hours under natural sunlight conditions, with 8 hours of radiation/day. Total photolytic transformation of MG in the closed batch system was observed after 210 hours at a temperature of 25 °C. During this photolytic transformation of MG, it has been shown that a large number of transformation products were generated. The kinetics of one of the, possible toxic, transformation products, 4-(dimethylamine)benzophenone (D20) indicated that photodegradation of D20 followed a similar photodegradation rate as MG (Pérez et al 2007).

The photodegradation of MG has been studied both under different pH values and varying amounts of TiO₂. Under the catalytic influence of TiO₂, the photodegradation rate increased substantially, resulting in 99.9 % degradation of the sample after 4 hours, indicating that the photodegradation of MG can be augmented substantially (Chen et al. 2006).

Fischer et al (2011) studied the influence of various wavelengths on the photodegradation of MG and MG carbinol, and concluded that MG carbinol is photodegraded more easily than MG. Although the photodegradation velocity of MG in the environment will depend mainly on the pH, it is clearly an important sink. The formation of a photocatalyst was proven during the irradiation of MG carbinol with wavelengths >365 nm.