Cyclohexylbenzene

Endpoint summary

Additional information

Four studies are available that assess the biodegradation of cyclohexylbenzene.

In the first study (Gagel, 1983), the biodegradation of cyclohexylbenzene is assessed via a River Die Away test. In this test, water from the Mississippi River is spiked with 50 ppb of cyclohexylbenzene. The decrease in concentration of cyclohexylbenzene in the test vessels was examined after 1, 3, 7, 14 and 28 days by GC FID analysis. The experiment demonstrated that the parent chemical disappeared from the test solution within 14 days. The half-life determined for cyclohexylbenzene is in the order of 6-8 days. Therefore, the study concludes that cyclohexylbenzene is readily biodegradable in Mississippi river water.

Two studies (Heim, 2001; and Saeger and Kuehnel, 1983) evaluate the ultimate biodegradation of cyclohexylbenzene by monitoring the CO2 evolution from the biometric flasks.

In the study by Heim, the test substance is exposed activated sludge from a wastewater treatment plant that receives predominantly domestic sewage at a test substance concentration of 20 mg carbon/L for 29 days. Sampling was performed on days 3, 6, 8, 10, 15, 20, 24 and 29. The percent theoretical (% ThCO2) for the test substance system was 14.3% and 1.3% for replicates 1 and 2, respectively, by day 29 of the study.

In the study by Saeger and Kuehnel, 20 mg/L of cyclohexylbenzene was exposed over a 55 -day period to a commercially available inoculum purported to be specifically adapted to hydrocarbons. The cyclohexylbenzene yielded a mean CO2 evolution of 12 percent.

Finally, a semi-continuous activated sludge (SCAS) test (Saeger and Tucker, 1973) was performed MCS 1567 on a mixture containing 70% cyclohexylbenzene and 30% biphenyl. The disappearance rates of the 2 constituents was determined via UV spectroscopic analysis on concentrated extracts from the samples. The activated sludge was pre-exposed to the test substance for 2 weeks prior to the determination of the degradation rate. Under the conditions of the SCAS test, the substance undergoes rapid primary degradation. Volatility losses were not a significant factor in the disappearance rate. The efficiency of the applied extraction protocol was confirmed via spiking experiments, thus indicating that the removal of the test compound was not related to mere adsorption to the sludge.

Overall, the available experimental data indicate that cyclohexylbenzene is inherently biodegradable and undergoes at least primary degradation, as demonstrated by the loss of parent chemical in the River Die Away test. The half-life for primary degradation is in the range of 6-8 days. Ultimate degradation occurs more slowly, with a degradation up to ca. 14% after 29 days, depending on the inoculum and test conditions.