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Under standard test conditions Malachite Green (MG) did not show to be readily biodegradable (0.3%, 14 days, OECD 301C), while testing for inherent biodegradability resulted in 82% degradation presumably over a 54 day time span in the OECD 302B test (Dystar, 1998), which leads to the conclusion that MG is poorly biodegradable in water. Degradation rates with various microorganisms varied but can reach up to 90% degradation within several days, indicating the potential of microorganisms to rapidly degrade MG.

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

Biodegradation 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 degradation.

Since the primary source of environmental pollution of MG is represented by industrial waste water, many studies of biodegradability by a variety of organisms (bacteria, algae, fungi, ) were carried out, in order to find (micro)organisms resistant to MG and capable of turning MG into a non-toxic compound with less environmental impact for use in water treatment plants. Several common species of microorganisms have been identified which are able to degrade MG up to 90% within several days. Furthermore sludge coming from industrial specific waste water treatment are sent to incinerator.

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 and discussed in details within the exposure scenario to avoid any release of the substance directly in the municipal waste water treatment.