MP99

Endpoint summary

Additional information

All studies performed to assess the environmental fate of cresols are performed on the single isomers. None of the reported studies in this chapter examined the behaviour of the isomer mixture. Depending up on the endpoint only the most critical result of all three isomers is considered for the assessment of the cresol mixture (e.g. bioaccumulation) or the most relevant result of every single isomer is assessed (e.g. biodegradation).

 

Abiotic degradation

The cresol isomers are supposed to degrade quickly in air. Experiments on reactivity with OH radicals revealed half-lives of 3.8 to 9 hours. Photodegradation in water takes a bit longer. Half-lives of 11 to 21 days were found on o- and p-cresol, respectively, showing that the isomers also undergo abiotic degradation by irradiation in aquatic environments. Photolytic degradation is expected to occur due to the presence of an aromatic ring in the chemical structure of molecules which acts as chromophore. No experimental data is available on hydrolysis. With regard to its chemical structure the cresol isomers are not expected to hydrolyse under environmental conditions.

 

Biotic degradation

Numerous studies on biodegradation of cresol isomers are available. Studies according or similar to OECD 301 showed that all three isomers are readily biodegradable. Studies on adapted inoculum also revealed inherent biodegradation. Under anaerobic conditions only m- and p-cresol could be degraded, based on measurements of CH4 and CO2 evolution. As all cresol isomers are readily biodegradable further testing on endpoints like biodegradation simulation tests, biodegradation in soil, and adsorption/desorption is not necessary. However, as studies are available on these endpoints they are reported herein. In simulation tests using natural sediment and surface water as inoculum m- and p-cresol could be degraded under aerobic and anaerobic conditions. Tests in sandy loam soils as well showed biodegradation of the cresols. Half-lives between 0.6 and 11.3 days were found in these soils. Summing up all data available the cresol isomers were biodegradable under almost all test conditions. Nevertheless there is a hint that biodegradation of o-cresol is hindered under anaerobic conditions.

 

Bioaccumulation

Bioaccumulation studies are available for o-cresol and m-cresol. Based on experimentally determined BCF values of 10.7 (o-cresol) and 20 (m-cresol), and based on log Kow values of 1.94 to 1.96 o-, m-, and p-cresol are judged to have a low bioaccumulation potential.

 

Transport and distribution

The adsorption behaviour of o-, m-, and p-cresol to organic carbon in soil was studied in batch equilibrium methods similar to OECD 106. Koc values between 22 and 49 were found in these studies. o-Cresol also was tested in a non-guideline study which showed the highest Koc value of 56. Based on these low Koc values cresol isomers are expected not to persist in soil, but pass into the groundwater. Experimentally determined Henry’s Law constants range between 0.087 Pa*m³/mol and 0.15 Pa*m³/mole, indicating a low volatilization of cresols from the aqueous phase. Findings on adsorption behaviour and volatility suggest water to be the main target compartment of cresols in the environment.