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Environmental fate & pathways

Biodegradation in water: screening tests

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Description of key information

o-Cresol is readily biodegradable under aerobic conditions in freshwater. It is inherently biodegradable, but not anaerobically biodegradable.

Key value for chemical safety assessment

Biodegradation in water:
readily biodegradable

Additional information

Serveral experiments on biodegradability are available for o-cresol.

The test system and test conditions used in a test on ready biodegradability are similar to those described in the OECD guideline 301 D, e.g. a high substance/inoculum ratio and the use of a non-adapted inoculum. The specific oxygen uptake curves are reported. After a short lag phase a plateau is reached within 10 days. After 20 days 86 % of o-cresol has been degraded. A half-life time of 2 to 3 days is reported.

The kinetics of o-cresol using an electrolytic respirometry test comparable to OECD guideline 301 C was assessed. Activated sludge from a wastewater treatment plant receiving predominantly domestic sewage was used as inoculum in a concentration of 30 mg/l. Within an incubation period of 40 days degradation of o-cresol (initial concentration 100 mg/l) was 80 %. The specific oxygen uptake curves are not reported. However, the authors state that all test compounds revealed the same pattern: the lag phase, biodegradation phase and the plateau region within a period of 10 days.

The inherent degradability of o-cresol was studied in a test similar to OECD guideline 302 B. Using an adapted activated sludge, o-cresol degraded to 95 % within 5 days. The initial degradation rate was 54 mg COD g-1 h-1. In a study performed according to OECD guideline 302 B, a degradation of 100 % after within 7 days was reported.

Anaerobic biodegradation was examined in an extensive study. Primary anaerobic sludges from 12 treatment plants receiving mainly domestic wastewater were diluted to 10 % in a mineral salt medium and incubated with 30 mg o-cresol/l for 8 weeks. Degradation was followed by CH4 and CO2 evolution. For o-cresol, no anaerobic degradation was observed in any sludges.