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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

The chlorinated isocyanurates are unstable in the environment, because the free available chlorine is rapidly reduced.  CYA, or its salt, is the stable degradation product. Therefore, CYA, or it sodium salt, is the substance of interest for the environmental fate studies.
Supporting information as cited in the literature has been provided which demonstrates that the biodegradation of cyanuric acid is dependent on the specific microorganisms present.

Key value for chemical safety assessment

Additional information

TCCA and NaDCC by analogy are not readily biodegradable (2% biodegradation in 28 days), however, it is considered that the substances would be biodegradable at a level below the inhibitory concentration to sewage sludge micro-organisms.

Normally, cyanuric acid degrades very slowly under aerobic conditions since the majority of aerobic microorganisms do not possess the genes to produce the specific enzymes required to degrade cyanuric acid. As a result, cyanuric acid shows minimal biodegradation in standard screening tests conducted at atmospheric oxygen levels and with no acclimation.


However, cyanuric acid can be degraded much more rapidly if: 1) specific fungal or bacterial strains are present which contain the genes/enzymes required, 2) the microorganisms have been acclimated to cyanuric acid, and 3) organic nutrients are present for the microorganisms. Furthermore, since bacteria degrade cyanuric acid in order to obtain ammonia for use in synthesis of biomass, the biodegradation of cyanuric acid is normally more pronounced if the ambient conditions are nitrogen-limited, but will be less likely to occur if more readily degraded sources of ammonia-nitrogen are present.