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EC number: 284-895-5
CAS number: 84989-06-0
The fraction of tar acids, rich in 2,4- and 2,5-dimethylphenol, recovered by distillation of low-temperature coal tar crude tar acids.
TS was completely utilized within 21 to 30 days in unacclimated
sediment. p-Cresol degradation proceeded through p-hydroxybenzaldehyde
and p-hydroxybenzoate under methanogenic and denitrifying conditions.
Under methanogenic conditions, also oxidation to benzoic acid took place
Degradation intermediate (CAS No./EC No./EINECS Name): 123-08-0
Degradation intermediate (CAS No./EC No./EINECS Name): 65-85-0 200-618-2
Degradation intermediate (CAS No./EC No./EINECS Name): 99-96-7 202-804-9
p-Cresol was completely biodegraded within 4 weeks in a freshwater
sediment (Haeggblom et al., 1992)
Mineralization was rapid without a lag-phase. Pre-exposure did not
accelerate degradation. Kinetic of test substance degradation: ca. 50%
after 40 h, ca. 90% after 70 h
Degradation products: not measured
p-Cresol was rapidly biodegraded (ca. 90 % after 70 h) in water,
water-sediment-suspensions, and by
intact sediment-water cores (eco-cores) of marine, estuarine, and
freshwater origin. No lag-phase was observed, and pre-exposure did not
accelerate degradation (Van Veld and Spain 1983, Spain and Van Veld
Mineralisation of o-cresol was assayed for more than 29 weeks.
No significant mineralisation was observed.
o-Cresol was not biodegradaded under anaerobic conditions within 29
weeks in a freshwater sediment (Horowitz, 1982).
o-cresol was first transformed to three dihydroxytoluenes
The o-cresol metabolic pathway was examined by Masunaga (1986) using a
phenol-adapted activated sludge. About 90% of the o-cresol is degraded
after 24 hours and the metabolites also diminish significantly with
time. The primary metabolic step is the ring-hydroxylation yielding
isomers of dihydroxy-toluene (3-methyl-catechol, 4-methyl-resorcinol,
methylhydroquinone). Secondary degradation products are formed either by
further hydroxylation yielding trihydroxy and tetrahydroxy-toluenes or
by cleavage of the aromatic ring system.
Based on all the available information (weight-of-evidence) and
following an analogue read-across approach there is evidence that Tar
acids, Xylenol fraction (CAS 84989-06-0) has a low potential for
accumulation in water and sediment.
Van Veld and Spain (1983) demonstrated that p-cresol is rapidly degraded
under aerobic conditions in different parts of an aquatic estuary
system. From a river estuary, each 3 samples were taken from water,
sediment and intact eco-cores having an aerobic layer of detritus
overlying anaerobic sediment. Water and water/sediment samples were
incubated in the laboratory with 14C-labelled p-cresol and shaken in
flasks at 18 °C in the dark. p-Cresol was rapidly biodegraded (ca. 90 %
after 70 h) in water, water-sediment-suspensions, and by intact
sediment-water cores (eco-cores) of marine, estuarine, and freshwater
origin. No lag-phase was observed, and pre-exposure did not accelerate
degradation. Based on HPLC and 14CO2 measurements, half-lives between
9.4 and 43 h for p-cresol in water and between 5.9 and 11 h in
water/sediment systems were determined. In intact eco-cores, p-cresol
degraded with half-lives between 3.0 and 16 h.
Data from a simulation test on biodegradation in water and sediment are
available for o-cresol (Horowitz et al. 1982). In this non-guideline
study the degradation of o-cresol was followed for 29 weeks under
anaerobic conditions. Anoxic natural sediment and anaerobic natural
water were used. Removal of test substance was followed by HPLC. No
significant mineralization was observed during the study period.
Anaerobic degradation was also investigated for p-cresol in a study by
Häggblom et al. (1990). In contrast to the study with o-cresol by
Horowitz et al. (1982) p-cresol was completely biodegraded within 4
weeks in freshwater sediment. The study was conducted with natural
sediment samples from a freshwater pond under three reducing conditions,
i.e. denitrifying, sulfidogenic, and methanogenic. Experiments were
conducted at 30 °C in the dark. Loss of p-cresol (initial concentration
of 1 mmol/L) in all the anaerobic systems took initially 3 to 4 weeks.
In acclimated cultures p-cresol was degraded in less than a week.
p-Cresol was completely metabolized under denitrifying, sulfidogenic,
and methanogenic conditions, with formation of nitrogen gas, loss of
sulfate, and formation of methane and carbon dioxide, respectively.
p-Cresol metabolism proceeded through p-hydroxybenzaldehyde and
p-hydroxybenzoate under denitrifying and methanogenic conditions. These
compounds were rapidly degraded in cultures acclimated to p-cresol under
all three reducing conditions. These results suggest that the initial
pathway of p-cresol degradation is the same under denitryfying,
sulfidogenic, and methanogenic conditions and proceeds via oxidation of
the methyl substituent to p-hydroxybenzaldehyde and p-hydroxybenzoate.
The initial rate of p-hydroxybenzaldehyde degradation was high in both
the non-acclimated cultures and in the cultures acclimated to p-cresol,
suggesting that this step is nonspecific. Benzoate was additionally
detected as a metabolite following p-hydroxybenzoate in the methanogenic
cultures, but not in the denitrifying or sulfidogenic cultures. The
degradation pathway therefore may diverge after p-hydroxybenzoate
formation depending on which electron acceptor is available.
The o-cresol metabolic pathway was examined by Masunaga et al. (1983,
1986) using a phenol-adapted activated sludge. About 90% of the o-cresol
is degraded after 24 hours and the metabolites also diminish
significantly with time. The primary metabolic step is the
ring-hydroxylation yielding isomers of dihydroxy-toluene
(3-methyl-catechol, 4-methyl-resorcinol, methylhydroquinone). Secondary
degradation products are formed either by further hydroxylation yielding
trihydroxy and tetrahydroxy-toluenes or by cleavage of the aromatic ring
In summary screening data on several constituents demonstrated ready
biodegradability, among them the cresol isomers, some xylenol isomers
and mixed ethylphenols. Other xylenol isomers are inherently
biodegradable. In a test with a similar UVCB substance, i.e. Tar acids,
3,5-xylenol fraction, 39% degradation were observed after 28 days. Data
on biodegradation in water and sediment are available for o- and
p-cresol. Nevertheless, results of these investigations provide evidence
that these constituents will be ultimately degraded under aerobic
conditions with half-lives between 9.4 and 43 h for p-cresol in water
and between 5.9 and 11 h in water/sediment systems. In so-called
eco-cores, p-cresol degraded with half-lives between 3.0 and 16 h.
Although no significant mineralization was observed under anaerobic
conditions, this is not considered to be of concern, since due to ready
biodegradation it is unlikely that cresols released into waste / surface
waters will reach anaerobic zones. O-cresol was completely biodegraded
within at least 4 weeks in freshwater sediment and studies on the
metabolic pathway showed significant degradation after 24 hours with
subsequent significant diminishment of metabolites.
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