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Ecotoxicological information

Toxicity to microorganisms

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Description of key information

The lowest results is a 28 day NOEC of 16 mg/L for xylene isomers and a 24 hour IC50 of 96 mg/L for ethylbenzene.

Key value for chemical safety assessment

EC50 for microorganisms:
96 mg/L
EC10 or NOEC for microorganisms:
16 mg/L

Additional information

Biodegradation tests were carried out on all three xylene isomers following OECD 301F guidelines using a mixed inoculum of non-adapted sludge and soil micro-organisms. In the toxicity control vessels, containing the individual xylene isomers with the reference substance sodium benzoate, none of the xylene isomers exhibited inhibitory effects on the micro-organisms. The 28 day NOEC (nominal concentration) is therefore 16 mg/L for m-xylene and 16.2 mg/L for o-xylene and p-xylene.

The studies by TNO (Oldersma 2004) and Volskay and Grady (1988) both follow OECD 209. TNO (2004) used p-xylene as the test substance, Volskay and Grady (1988) tested both o- and p-xylene. Each of the tests used a single test concentration approximating the limit of solubility of the test substance. The EC50 was not observed in any of the tests. The study by TNO reports a 3 hour NOEC of 157mg/L. Volskay and Grady (1988) report a 30 minute EC50 (respiration inhibition) of >175 mg/L for o-xylene and >198 mg/L for p-xylene and therefore the EC50 are above the limit of solubility.

A non-guideline study by Blum and Speece (1991) used ethylbenzene as the test substance and reported a 24 hour IC50 for Nitrosomonas of 96 mg/L. This result is cited in the EU RAR (ECB 2007) along with a 15 hour IC50 of 130 mg/L for the inhibition of oxygen consumption of aerobic heterotrophs from the same study. The EU RAR also reports results for Volskay and Grady (1990), Krebs (1991) and earlier studies by Bringmann and Kuhn (1977, 1981) but, as more reliable data were available, these were not considered to be the key studies and so have not been included here.