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EC number: 202-049-5
CAS number: 91-20-3
Depending on the aquatic organism and developmental state (selected) acute aquatic EC/LC50s are:0.92 mg/l (24 hr LC 50, pink salmon),0.9-1.01 mg/l (48 hr LC50, pink salmon fry)1.6 mg/l (96 hr LC 50, rainbow trout), 2.1 mg/l (96 hr LC 50, coho salmon), 1.99 - 7.9 mg/l (96 hr LC50, fathead minnow).
The following discussion is partly quoted
from the EU RAR on naphthalene [EU RAR]:
There are a lot of data available on fish
and a wide range of species has been tested. The majority of the results
from short-term tests lie in the range 1-10 mg/l. 96-hour LC50 range
from 1.6 mg/l for rainbow trout to 150 mg/l for mosquito fish. All of
the organisms tested appear to show similar sensitivity in the
short-term tests. There is some evidence to suggest that naphthalene
exerts its toxic effect by narcosis. Acute toxicity values have been
predicted by Bol et al. (1993) using QSAR equations for chemicals that
act by narcosis. The predicted values were 7.8 mg/l (LC50 for fish), 6.1
mg/l (LC50 for daphnia) and 3.8 mg/l (EC50 for algae), all of which fit
closely the range of measured values whilst being towards the high end.
Care must be taken when interpreting data
from tests based on nominal concentrations because naphthalene can be
rapidly lost from solution. Rice and Thomas (1989) studied the acute
toxicity of naphthalene to pink salmon fry (Oncorhynchus gorbuscha) and
calculated a 96-hour LC50 of 0.96 mg/l. Two-day pre-treatment exposures
of between 52% and 87% of the control LC50 concentrations significantly
increased the tolerance of pink salmon fry to naphthalene. Even 12-hour
pre-treatment exposures of naphthalene (85% of LC50 concentration)
significantly increased the tolerance of the fry to naphthalene. Korn
and Rice (1981) found that the toxicity of naphthalene to Coho salmon
(Oncorhynchus kisutch) increased from eggs through early, mid and late
alevins to emergent fry. 96-hour LC50s ranged from >11.8 mg/l to 5.6
mg/l in static renewal tests.
in the laboratory, naphthalene will also evaporate in the environment
from compartments, thus showing a clear tendency to fade away (within
hours to days). This would lead to a more or less rapid elimination of
naphthalene out of the respective compartment and a decrease of
potential biological impact. Low levels of naphthalene do not
necessarily cause inhibition in organisms. In some instances increasing
tolerance towards naphthalene was observed and even stimulation e.g. of
growth or other parameters as compared to controls. This observation,
however, may not necessarily be interpreted as “positive” or
“beneficial” effects. However, against this background, LC50 of 0.9 mg/l
for freshwater fish and 2.4 mg/l for marine water fish are considered to
be sufficiently low to cover freshwater and marine fish respectively.
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