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Toxicity to microorganisms

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Description of key information

IC50: 29 mg/l (Nitrosomonas, ammonia consumption) 
IC50: 670 mg/l (Aerobic heterotrophs, inhibition of oxygen uptake)
NOEC: 1 mg/g sediment (dw) (Anaerobic salt marsh, methanogenesis, sulphate reduction and CO2 evolution)
NOEC < 100 mg/l and > 10 mg/l (Oxic sediment and anoxic sediment, short-term, for 3H-thymidine incorporation and 14C-glucose metabolism)
EC50: 1,154 mg/l (mixed microbial culture, biodegradation of various alcohols)
IC50: 188.85 mg/l (Tetrahymena pyriformis, 60-hour exposure, 50% inhibition of growth of population)

Key value for chemical safety assessment

EC50 for microorganisms:
29 mg/L
EC10 or NOEC for microorganisms:
10 mg/L

Additional information

The following discussion is partly quoted from the EU RAR on naphthalene [EU RAR]:

A limited set of studies regarding toxicity of naphthalene to microorganisms is available. Blum and Speece (1991) studied the effect of naphthalene on bacterial populations using IC50 tests. The inhibition of ammonia consumption was used as the criterion for the toxic inhibition of Nitrosomonas and an IC50 of 29 mg/l was reported. For aerobic heterotrophs, inhibition of oxygen uptake was used as the criterion for toxic inhibition and an IC50 of 670 mg/l was reported. Kiene and Capone (1984) studied the effect of naphthalene (1,000 µg/kg) on methanogenesis, sulphate reduction and carbon dioxide evolution of anaerobic salt marsh sediment over a 7- to 9-day period. Initially, methanogenesis was significantly inhibited but towards the end of the experiment there was significant stimulation of methanogenesis. Sulphate reduction was significantly inhibited and carbon dioxide evolution was only significantly inhibited in one of three experiments. Bauer and Capone (1985) studied the metabolism of 14C-glucose and the incorporation of [methyl-3H]thymidine by aerobic and anaerobic marine sediment microbes exposed to naphthalene. Concentrations of 100 mg/l significantly inhibited glucose metabolism and thymidine incorporation in both aerobic and anaerobic sediment. Vaishnav (1986) studied the effect of naphthalene on the biodegradation of primary alcohols by a mixed microbial culture. An IC50, based on maximum observed biodegradation rate, was calculated to be 1.154 mg/l. Schultz et al. (1983) exposed the microorganism Tetrahymena pyriformisto naphthalene and studied the effect on biological activity monitored as population growth. A graded series of 4 naphthalene concentrations were tested and cultures without toxicant were used as controls. Incubation of cultures at each concentration was carried out in the dark for 60 hours. The concentration that inhibits 50% growth of population following 60-hour exposure was calculated to be 188.85 mg/l.

[EU RAR] European Union Risk Assessment Report NAPHTHALENE [CAS No: 91-20-3; EINECS No: 202-049-5] RISK ASSESSMENT European Communities, 2003 []