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EC number: 203-396-5
CAS number: 106-42-3
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.
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
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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