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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

Non-standard biodegradation tests and a ready-biodegradation test conducted under aerobic conditions clearly showed that naphthalene is easily or even readily biodegradable. Under this premise, a negative result obtained under MITI(II) conditions is considered to be invalid. 

Key value for chemical safety assessment

Biodegradation in water:
inherently biodegradable

Additional information

Rapid biodegradation in water occurred especially in those tests in which aerobic or denitrifying conditions were predominant and microorganisms already acclimated to the exposed substances. After a short lag period (1.2 – 12 days) naphthalene was extensively degraded within 5 – 15 days.

Apparently contradicting results have been found in two standardised tests: In a MITI-II test for inherent biodegradability similar to OECD TG 302C performed under the Japanese Chemical Inspection & Testing Institute, no biodegradation of the test substance naphthalene was observed (2% degradation within 4 weeks). This officially published negative result is conflicting with a positive finding obtained under MITI(I) conditions by the Mitsubishi-Kasai Institute (Yoshida et al. 1983).

That poor outcome in the MITI(II) test can be explained by the stringent, negative-selective pre-treatment of the natural microflora for the preparation of the inoculum, a procedure that favours the loss of indigenous potent micro-organisms for special properties of decomposition.

Given this, it can be concluded that the MITI(II) test produced a false-negative result, while naphthalene is rapidly/easily biodegradable most of the time, at least inherently biodegradable under less favorable conditions.