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EC number: 284-892-9
CAS number: 84989-04-8
The fraction of tar acid rich in 3- and 4-methylphenol, recovered by distillation of low-temperature coal tar crude tar acids.
All studies performed to assess the environmental fate of cresols
are performed on the single isomers. None of the reported studies in
this chapter examined the behaviour of the isomer mixture. Depending up
on the endpoint only the most critical result of all three isomers is
considered for the assessment of the cresol mixture (e.g.
bioaccumulation) or the most relevant result of every single isomer is
assessed (e.g. biodegradation).
The cresol isomers are supposed to degrade quickly in air.
Experiments on reactivity with OH radicals revealed half-lives of 3.8 to
9 hours. Photodegradation in water takes a bit longer. Half-lives of 11
to 21 days were found on o- and p-cresol, respectively, showing that the
isomers also undergo abiotic degradation by irradiation in aquatic
environments. Photolytic degradation is expected to occur due to the
presence of an aromatic ring in the chemical structure of molecules
which acts as chromophore. No experimental data is available on
hydrolysis. With regard to its chemical structure the cresol isomers are
not expected to hydrolyse under environmental conditions.
Numerous studies on biodegradation of cresol isomers are
available. Studies according or similar to OECD 301 showed that all
three isomers are readily biodegradable. Studies on adapted inoculum
also revealed inherent biodegradation. Under anaerobic conditions only
m- and p-cresol could be degraded, based on measurements of CH4 and CO2
evolution. As all cresol isomers are readily biodegradable further
testing on endpoints like biodegradation simulation tests,
biodegradation in soil, and adsorption/desorption is not necessary.
However, as studies are available on these endpoints they are reported
herein. In simulation tests using natural sediment and surface water as
inoculum m- and p-cresol could be degraded under aerobic and anaerobic
conditions. Tests in sandy loam soils as well showed biodegradation of
the cresols. Half-lives between 0.6 and 11.3 days were found in these
soils. Summing up all data available the cresol isomers were
biodegradable under almost all test conditions. Nevertheless there is a
hint that biodegradation of o-cresol is hindered under anaerobic
Bioaccumulation studies are available for o-cresol and m-cresol.
Based on experimentally determined BCF values of 10.7 (o-cresol) and 20
(m-cresol), and based on log Kow values of 1.94 to 1.96 o-, m-, and
p-cresol are judged to have a low bioaccumulation potential.
Transport and distribution
The adsorption behaviour of o-, m-, and p-cresol to organic carbon
in soil was studied in batch equilibrium methods similar to OECD 106.
Koc values between 22 and 49 were found in these studies. o-Cresol also
was tested in a non-guideline study which showed the highest Koc value
of 56. Based on these low Koc values cresol isomers are expected not to
persist in soil, but pass into the groundwater. Experimentally
determined Henry’s Law constants range between 0.087 Pa*m³/mol and 0.15
Pa*m³/mole, indicating a low volatilization of cresols from the aqueous
phase. Findings on adsorption behaviour and volatility suggest water to
be the main target compartment of cresols in the environment.
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