Tar acids, methylphenol fraction

Biodegradation in water: screening tests

Description of key information

All cresol isomers (o-, m- and p-cresol) are readily biodegradable
o-, m-, and p-cresol: BOD 80% - 95% (OECD 301 C)
o-cresol: BOD = 86% (OECD 301 D)
m-cresol: BOD = 90% (OECD 301 D)

Additional information

studies on ready biodegradability 

Desai et al. (1990) determined the kinetics of o-, m- and p-cresol using an electrolytic respirometer test comparable to OECD guideline 301 C. 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 cresol isomers (initial concentration 100 mg/L) was in the range of 80% to 95%. The specific oxygen uptake curves of the cresols are not reported. However, the authors state that all test compounds revealed the same pattern: the lag phase, biodegradation phase and the plateau phase within a period of 10 days. Therefore, it can be concluded from this test that o-, m- and p-cresol are readily biodegradable.

The test system and test conditions used by Buzzel (1968) 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.

Biodegradation of m-cresol was tested in aquatic phase according to OECD Guideline 301 D (Ready Biodegradability: Closed Bottle Test). Degradation was 90% after 28 d and the 10 d window was fulfilled. Thus m-cresol is judged to be readily biodegradable (Bayer, 1988).

 

studies on inherent biodegradability 

All cresol isomers are inherently degradable as shown by tests according to the OECD guideline 302 B. After a lag-period of 2 days 96% of the added m-cresol and 100% of the added p-cresol were degraded within 10 days, and a degradation of 100% within 7 days was observed for o-cresol (Wellens, 1990). The inherent biodegradability was also studied by Pitter (1976) in a test similar to OECD guideline 302 B. Using an adapted activated sludge, o-cresol degraded to 95% and m- and p-cresol to 96% each within 5 days. 

 

anaerobic test systems

The most extensive study on o-cresol was conducted by(1981). 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 CH₄and CO₂evolution. For o-cresol, no anaerobic degradation was observed in any sludge.

In contrast to these findings p-cresol and m-cresol are biodegradable under anaerobic conditions. As measured from methane release and carbon dioxide formation m- and p-cresol are mineralized by anaerobic sludges from wastewater treatment plants (Shelton and Tietje 1981, 1984; Battersby and Wilson 1988, 1989).

 

marine test system

Biodegradation of p-cresol was also tested in seawater where it was biodegradable as well (Boyd and Carlucci 1993).