Registration Dossier
Registration Dossier
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EC number: 203-396-5 | CAS number: 106-42-3
Toxicity to microorganisms
Administrative data
Link to relevant study record(s)
Description of key information
The toxicity controls from the biodegradation studies on the xylene isomers indicate that the substances are not inhibitory to micro-organisms, with a 28 day NOEC of 16 mg/L.
The estimated EL50 values from TLM QSAR were 71.287 - 90.449 mg/L. The estimated NOELR values from TLM QSAR were 13.656 - 17.327 mg/L.
Key value for chemical safety assessment
- 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 TLM-EqP modeling framework was used to support values derived experimentally and are presented as supporting studies.
The estimated EL50 values from TLM QSAR were 71.287 - 90.449 mg/L, and the estimated NOELR values from TLM QSAR were 13.656 - 17.327 mg/L.
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