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Screening tests for biodegradation of Reactive Blue 203 and its structural analogues in water showed that the test item is not readily or inherently biodegradable. However, it is rapidly hydrolysed with a half-life of 2 to 6 days at pH 7. When Reactive Black 5 was applied to a sediment/water test system at a final concentration of 1 mg/kg, the test item was rapidly degraded. The DT50 of Reactive Black 5 was 2 days. After 3 to 6 days, only 10% of the applied Reactive Black 5 could be found. All metabolites decreased at the end of the test period to levels around the lower level of quantification. Consequently, an accumulation of metabolites could be excluded. The majority of the metabolites of Reactive Black 5 were deposited in form of non-extractable residues in sediment during test phase. After about 1 month, mineralization of the metabolites started.

Hence, it is expected that Reactive Blue 203 is rapidly removed from the environment by abiotic degradation and does not persist in the environment.