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

Endpoint summary

Description of key information

Not readily biodegradable

Additional information

Under standard test conditions in DyStarColours Distribution GmbH reports (1998) Malachite Green is indicated as not readily biodegradable (0.3 %, 14 days, OECD 301C); these values are confirmed by EpiSuite prediction. A possible inherent biodegradation is indicated in DyStarColours Distribution GmbH reports (1998) where a value of 82 % 9 of degradation in Zahn-Wellens test is reported, however any detail is missing about time and testing conditions.

 

pH has a significant effect on the discolourization of MG, with an increase in decolourization when pH increases and a maximum at pH 9.

The transformation has mostly been tested by evaluating the decolourization of MG over time. In most cases the influence of sorption or pH change and subsequent decolourization has been noted but not taken into account in the conclusions or discussion of the studies. The mentioned interacting effects have sometimes been studied separately, but not in combination with each other; it can be only stated that combined effects usually contribute to improve the yield of discolorization.

 

The discolourization has not to be considered as an indication of MG degradation, in fact colourless can be perform interrupting the conjugation.

As mentioned in the stability endpoint, the MG undergoes transformation to the coloured cations (carbonil), by the inclusion of an oxygen atom on the triphenylic structure. The percentage of the dye transformation is dependent on the hydrogen-ion concentration of the system and the greater the hydrogen-ion concentration.

Most studies conducted on the biodegradation of MG have focused on the decolourisation of the test solution, which has been obtained using for instance bacteria, fungi or algae. The study by Daneshvar et al, 2006 shows thatCosmarium microalgae species have the capability to decolorize MG. Daneshvar et al further studied the effect of initial concentration, pH and temperature on the decolorization efficiency of Cosmarium species and determined that MG was decolorized 80 - 90 % under environmental pH conditions (i.e. pH 5-8). Furthermore they determined that, with a standard European temperature of 12 °C, Cosmarium species decolorized MG for 60 % and that increased decolourization (max > 95 %) occurred with increasing temperature (max 45 °C). The decolorization rate of MG by Cosmarium microalgae increased with an increased initial concentration of MG, an observation shared with the decolorization rate of MG byKocuria roseaas shown by Parshetti et al, 2006. However, Ayed et al, 2009 reported a decrease in decolorization by the soil bacillus S. paucimobilis with increasing initial MG concentration and Jadhav et al, 2006 determined that the yeast Saccharomyces cerevisiae MTCC 463 decolourized MG by biosorption and biodegradation and about 85% decolorization in distilled water (< 7 h), and 95.5 % in 5 % glucose medium (< 4 h) was observed, under aerobic conditions at room temperature. The fungus Cunninghamella elegans(ATCC 36112) is able to degrade MG with a first order rate constant of 0.029 mmol/h (mg of cells), (Cha et al, 2001). In this study the biodegradation pathway has been elucidated for MG and its primary transformation product LG. Both MG and LG follow the same reduction pathway to form N-demethylated and N-oxidized metabolites including primary and secondary arylamines. Isolates of another fungal species Fusarium solari (Martius) Saccardo from dye containing effluents have been shown to degrade MG for 96 % after 2 days of shaking (Hazrat, 2010).

 

Biodegradation in soil and sediment is not considered because direct and indirect exposure of soil and sediment is unlikely due to the risk management measures that will be applied at industrial level to avoid any release of the substance directly in the municipal waste water treatment.