Aerobic and anaerobic biodegradation of phenol derivatives in various paddy soils

Microbiological degradation of phenol and some of its alkyl-derivatives (p-cresol, 4-n-propylphenol, 4-i-propylphenol, 4-n-butylphenol, 4-sec-butylphenol, 4-t-butylphenol, and 4-t-octylphenol) was examined under both aerobic and anaerobic conditions in seven Japanese paddy soils. Aerobic biodegradation of phenol derivatives was detected in all the paddy soils examined. The half-lives ranged from 2 to 19 days. The aerobic degradation rate of 4-t-octylphenol was correlated inversely with the total carbon contents of paddy soils, and there were significant inverse correlations between the aerobic degradation rate and the size of alkyl groups of alkylphenols. Anaerobic biodegradation of phenol and p-cresol was detected in three soils with the half-lives ranging from 24 to 260 days for phenol and from 11 to 740 days for p-cresol, respectively. The three soils were characterized by low contents of nitrate and iron oxides. Other soil properties did not show any significant correlations with the anaerobic degradation rates. In one soil, we found for the first time anaerobic biodegradation of 4-n-propylphenol. However, the other five compounds (4-i-propylphenol, 4-n-butylphenol, 4-sec-butylphenol, 4-t-butylphenol and 4-t-octylphenol) were not degraded over 224 days of incubation. These results suggest that phenol and all the alkylphenols were degraded within several days when paddy soil is not flooded and so under aerobic conditions. Under flooded and anaerobic conditions, 4-n-propylphenol would be degraded as well as phenol and p-cresol while alkylphenols with long and branched alkyl chains were hardly degraded at all.