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Environmental fate & pathways

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The chemical class of reactive dyes is generally not considered to be biodegradable at all. For the present substance Reactive Red 065, only few data are available to cover this endpoint. In the past BOD5 and COD values have been determined to assess the behavior of the test substance in industrial sewage treatment plants. The calculated BOD5/COD quotient is used to estimate the rate of biodegradation within the sewage treatment plant. Total organic carbon (TOC) of Reactive Red 065 was found to be 31 % after 31 days. The BOD5 was fond to be 42 mg O2/g while COD was 688 mg O2/g; so the BOD5/COD ratio calculated as 0.06. Based on this value Reactive Red 065 should not be considered as not biodegradable.

By the nature of their design and use, reactive dyes are not intended to be readily biodegradable as this would assist in the rapid destruction of the chemical, rendering it unfit for purpose. As such, it is accepted that such substances are not readily biodegradable under relevant environmental conditions. A published study (Pagga & Brown, 1986) describes the results of the testing of 87 dyestuffs in short-term aerobic biodegradation tests. The authors of this publication concluded that dyestuffs are very unlikely to show any significant biodegradation in such tests and that there seems little point in carrying out such test procedures on dyestuffs.

There are ISO, European, American (AATCC) and national standards available for the colour fastness of dyes. Dyes are required to have specific fastness properties. If the dyes were biodegradable, it would not be possible for them to have these fastness properties.



Pagga U, Brown D (1986) The degradation of dyestuffs: Part II. Behaviour of dyestuffs in aerobic biodegradation tests. Chemosphere 15: 479-491.

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