Naphthalene

Short-term toxicity to fish

Description of key information

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).

Key value for chemical safety assessment

Fresh water fish

Fresh water fish

Effect concentration:

0.9 mg/L

Marine water fish

Marine water fish

Effect concentration:

2.4 mg/L

Additional information

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.

Like 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.

[EU RAR] European Union Risk Assessment Report NAPHTHALENE [CAS No: 91-20-3; EINECS No: 202-049-5] RISK ASSESSMENT European Communities, 2003 [http://ecb.jrc.ec.europa.eu/esis/]