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Biodegradation in water and sediment: simulation tests

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Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Anaerobic p-cresol degradation by sediment samples from a freshwater pond under three reducing conditions: denitrifying, sulfidogenic, and methanogenic
GLP compliance:
no
Oxygen conditions:
anaerobic
Inoculum or test system:
natural sediment
Duration of test (contact time):
>= 3 - <= 4 wk
Initial conc.:
1 mmol/L
Based on:
test mat.
% Degr.:
100
Parameter:
test mat. analysis
Sampling time:
4 wk
Remarks on result:
other: Under denitrifying conditions 10 d for 100 % mineralization
Compartment:
entire system
DT50:
ca. 3 wk
Type:
not specified
Temp.:
30 °C
Transformation products:
yes
No.:
#1
Details on transformation products:
Several intermediates of degradation identified. Final degradtion products were methane and carbon dioxide
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): 123-08-0 204-599-1 4-hydroxybenzaldehyde
Degradation intermediate (CAS No./EC No./EINECS Name): 65-85-0 200-618-2 benzoic acid
Degradation intermediate (CAS No./EC No./EINECS Name): 99-96-7 202-804-9 4-hydroxybenzoic acid

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): 123-08-0 204-599-1 4-hydroxybenzaldehyde

Degradation intermediate (CAS No./EC No./EINECS Name): 65-85-0 200-618-2 benzoic acid

Degradation intermediate (CAS No./EC No./EINECS Name): 99-96-7 202-804-9 4-hydroxybenzoic acid

Executive summary:

p-Cresol was completely biodegraded within 4 weeks in a freshwater sediment (Haeggblom et al., 1992)

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Biodegradation test with natural microorganism communities from water and sediment in the form of e.g. "ecocores"
GLP compliance:
no
Radiolabelling:
yes
Remarks:
[ring-U-14C] p-cresol
Oxygen conditions:
aerobic
Inoculum or test system:
natural water / sediment
Details on source and properties of surface water:
Adaptation of natural microbial communities was measured in ecocore test systems filled with sediment and natural water collected at a river. Parent compound disappearance and mineralization were monitored.
Details on inoculum:
200 μg/L related to Test substance
Duration of test (contact time):
120 h
Compartment:
other: water, material (mass) balance
% Recovery:
37.7
St. dev.:
6.3
Compartment:
other: sediment, material (mass) balance
% Recovery:
48.4
St. dev.:
9.6
Remarks on result:
other: see "any other information on results incl. tables"
Remarks:
see "any other information on results incl. tables"
Compartment:
water
DT50:
>= 9.5 - <= 43 h
Type:
(pseudo-)first order (= half-life)
Temp.:
18 °C
Compartment:
sediment
DT50:
>= 5.9 - <= 11 h
Type:
(pseudo-)first order (= half-life)
Temp.:
18 °C
Compartment:
entire system
DT50:
>= 3 - <= 16 h
Type:
(pseudo-)first order (= half-life)
Temp.:
18 °C
Remarks on result:
other: "ecocores" (sediment cores)
Transformation products:
not measured
Details on results:
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

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

Validity criteria fulfilled:
not applicable
Executive summary:

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 1983).

Endpoint:
biodegradation in water: sediment simulation testing
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Examination on anaerobic degradation of o-cresol by lake sediments.
Degradation was followed by measuring disappearance of test substance.
GLP compliance:
no
Oxygen conditions:
anaerobic
Inoculum or test system:
natural sediment
Details on source and properties of surface water:
Anoxic sediments were covered with a 2-3 m layer of anaerobic water except for short periods during spring and fall overturn
Details on source and properties of sediment:
Anoxic sediments from a pelagic region of hypereutrophic Wintergreen Lake (Kalamazoo County, MI)
Details on inoculum:
Sediments were handled under 90% N2 and 10% H2 and preincubated in bottles (100 mL inoculum/160 mL bottle volume) for 24 h to stabilise after disturbance
Duration of test (contact time):
> 29 wk
Initial conc.:
100 - 800 µmol/L
Based on:
test mat.
Remarks on result:
other: see "any other information on results incl. tables"
Remarks:
see "any other information on results incl. tables"
Remarks on result:
other: see "any other information on results incl. tables"
Remarks:
see "any other information on results incl. tables"
Transformation products:
not specified

Mineralisation of o-cresol was assayed for more than 29 weeks.

No significant mineralisation was observed.

Validity criteria fulfilled:
not applicable
Executive summary:

o-Cresol was not biodegradaded under anaerobic conditions within 29 weeks in a freshwater sediment (Horowitz, 1982).

Endpoint:
biodegradation in water: sewage treatment simulation testing
Type of information:
experimental study
Adequacy of study:
weight of evidence
Reliability:
2 (reliable with restrictions)
Rationale for reliability incl. deficiencies:
study well documented, meets generally accepted scientific principles, acceptable for assessment
Qualifier:
no guideline followed
Principles of method if other than guideline:
Biodegradation process by phenol acclimated activated sludge; identifying of metabolic intermediates
GLP compliance:
no
Radiolabelling:
no
Oxygen conditions:
aerobic
Inoculum or test system:
activated sludge, adapted
Details on inoculum:
Activated sludge was cultured by a medium containing phenol as the carbon source over a period of more than a year in a 4-l laboratory unit, concentration of microorganism in dry weight was 950 mg/L
Duration of test (contact time):
24 h
Initial conc.:
200 mg/L
Based on:
test mat.
Remarks on result:
other: see "any other information on results incl. tables"
Remarks:
see "any other information on results incl. tables"
Remarks on result:
other: see "any other information on results incl. tables"
Remarks:
see "any other information on results incl. tables"
Transformation products:
yes
No.:
#1
No.:
#2
No.:
#3
Evaporation of parent compound:
no
Volatile metabolites:
no
Residues:
not specified

o-cresol was first transformed to three dihydroxytoluenes

Validity criteria fulfilled:
not applicable
Executive summary:

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.

Description of key information

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.

Key value for chemical safety assessment

Additional information

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 system.

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.

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.