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EC number: 202-049-5
CAS number: 91-20-3
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.
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.
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
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
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