Abstract
Herbicide-derived chloroaniline residues are immobilized in soil by formation of humic complexes. Experiments with soil-bound radiolabeled 3,4-dichloroaniline demonstrate that 24CO2, is released from soil at the rate of 1 percent per week. The rate of 14CO2 release was not significantly influenced by variations of pH from 5.0 to 8.0, or by moisture contents between 50 percent and 70 percent of the holding capacity. Small amounts of glucose (30 mg per 50 g soil) did not influence 14CO2 release, but large amounts (250 mg per 50 g soil) severely inhibited the release of radiocarbon. The temperature optimum for 14CO2 release was found to be 37°C. Sterilized and anaerobic soils released less than 4 percent of 14CO2 as compared to the nonsterile aerobic control. The overall rate of microbial activity as measured by total CO2 evolution was not significantly affected by humus-bound 3,4-dichloroaniline. Serving as the only organic substrate in a mineral salts solution, biodegradation of the humic-3,4-dichloroaniline complex by two soil fungi was studied. Penicillium frequentans in two weeks released 7.3 mmol of total CO2, but only 0.5 percent of the radiocarbon. In contrast, Aspergillus versicolor released only 4.7 mmol of total CO2, but as much as 1.3 percent of the radiocarbon. Analyses of the residual humic acid complex and its metabolites indicate two distinct modes of attack by the two soil fungi. Herbicide-derived chloroaniline residues are immobilized in soil by formation of humic complexes. Experiments with soil-bound radiolabeled 3,4-dichloroaniline demonstrate that 24CO2, is released from soil at the rate of 1 percent per week. The rate of 14CO2 release was not significantly influenced by variations of pH from 5.0 to 8.0, or by moisture contents between 50 percent and 70 percent of the holding capacity. Small amounts of glucose (30 mg per 50 g soil) did not influence 14CO2 release, but large amounts (250 mg per 50 g soil) severely inhibited the release of radiocarbon. The temperature optimum for 14CO2 release was found to be 37°C. Sterilized and anaerobic soils released less than 4 percent of 14CO2 as compared to the nonsterile aerobic control. The overall rate of microbial activity as measured by total CO2 evolution was not significantly affected by humus-bound 3,4-dichloroaniline. Serving as the only organic substrate in a mineral salts solution, biodegradation of the humic-3,4-dichloroaniline complex by two soil fungi was studied. Penicillium frequentans in two weeks released 7.3 mmol of total CO2, but only 0.5 percent of the radiocarbon. In contrast, Aspergillus versicolor released only 4.7 mmol of total CO2, but as much as 1.3 percent of the radiocarbon. Analyses of the residual humic acid complex and its metabolites indicate two distinct modes of attack by the two soil fungi. © Williams & Wilkins 1974. All Rights Reserved.