MICROBIAL RELEASE OF 2,4-DICHLOROPHENOL BOUND TO HUMIC-ACID OR INCORPORATED DURING HUMIFICATION

The microbial release of 14C-labeled 2,4-dichlorophenol (DCP) bound to synthetic and natural humic materials or polymerized by enzymes was investigated to evaluate the possibility of future adverse effects if binding or polymerization is used for decontamination purposes. After 12 wk of incubation with microorganisms obtained from a forest soil, the amounts of substances released into the media were very small (maximum 2.2% of the initially bound 14C) without regard to the kind of the polymer into which 14C-DCP was incorporated. Most of the radioactivity (46.2 to 80.8%) remained bound to the precipitated humic materials or in the DCP-polymer (90.1 to 97.0%). Certain amounts of the released substances evolved in the form of 14CO2 (1.0 to 9.4% from humic materials and 0 to 0.5% from a DCP-polymer). The rate of mineralization differed depending on the type of DCP binding - surface-bound or incorporated during synthesis of humic acid - and on the kind of polymer to which 14C-DCP was attached. The release into the media and 14CO2 evolution for synthetic and natural humic acids was essentially the same. When only DCP was present in the growth medium, the formation of 14CO2 was less than from a DCP-humic acid complex; this may indicate that 14CO2 from a DCP-humic acid complex originated mostly from DCP derivatives. The data obtained for DCP did not provide any evidence for a delayed pollution problem associated with polymerization or binding of xenobiotics to humic acids.