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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Triclosan is not readily biodegradable (according to OECD criteria), but inherently biodegradable.

Its metabolite methyl-triclosan (CAS 4640 -01 -1) is also inherently biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

The ready biodegradability of Triclosan was tested by several guideline studies. In a study following OECD guideline 301 B the O2 consumption of activated sludge fed with 10 or 20 mg/l test substance was tested. After 28 days a degradation rate of 18 % at a test substance concentration of 20 mg/l was detected. At a test substance concentration of 10 mg/l 37 % of Triclosan were degradaded after 28 days (Ciba-Geigy 1989). Comparable results were derived in a study conducted according to OECD guideline 301 C. Based on O2 consumption a degradation rate of 0 % was determined after 28 days (Ciba-Geigy 1990).

In guideline study on inherent biodegradability according to OECD 302 B a elimination rate of 99.4 % was detected after 14 days of incubation (Ciba-Geigy 1999). Thus the substance is inherently biodegradable. This result is supported by a study on mineralisation of Triclosan in a continuous activated sludge system (CAS). The substance was added continously to activated sludge for 1 ½ month. The degradation rate was determined by analysing the Triclosan concentration after ca. 50 days. The removal rate was 98.2 - 99.3 % (Ciba Specialty Chemicals 1998). In a second CAS test the concentration of Triclosan was constantly increased from 40 µg/l to 200 µg/l. A degradation rate of 75 -88 % was determined by radiochemical measurement (Procter & Gamble 1992). The results are supported by a third CAS test. The test run for 71 days. Based on CO2 evolution a degradation rate of 80 - 98.5 % was recorded (Federle et al. 2002). Under anaerobic conditions less than 10 % degradation were observed (Colgate-Palmolive 1994).

Methyltriclosan (CAS 4640 -01 -1) is regarded as one of the metabolites of triclosan. In an enhanced OECD 301 B study under GLP, methyltriclosan was not readily biodegradable, but proved to be inherently biodegradable (BASF SE; 2012; project no. 22G0533/10G059).