EFFECT OF MINERAL AND ORGANIC SOIL CONSTITUENTS ON MICROBIAL MINERALIZATION OF ORGANIC-COMPOUNDS IN A NATURAL SOIL

This research addressed the effect of mineral and organic soil constit uents on the fate of organic compounds in soils. Specifically, it soug ht to determine how the associations between organic chemicals and dif ferent soil constituents affect their subsequent biodegradation in soi l. Four C-14-labeled surfactants were aseptically adsorbed to montmori llonite, kaolinite, illite, sand, and humic acids. These complexes wer e mixed with a woodlot soil, and (CO2)-C-14 production was measured ov er time. The mineralization data were fitted to various production mod els by nonlinear regression, and a mixed (3/2)-order model was found t o most accurately describe the mineralization patterns. Different mine ralization patterns were observed as a function of the chemical and so il constituents. Surfactants that had been preadsorbed to sand or kaol inite usually showed similar mineralization kinetics to the control tr eatments, in which the surfactants were added to the soil as an aqueou s solution. Surfactants that had been bound to illite or montmorilloni te were typically degraded to lesser extents than the other forms, whi le surfactant-humic acid complexes were degraded more slowly than the other forms. The desorption coefficients (K-d) of the soil constituent -bound surfactants were negatively correlated with the initial rates o f degradation (k(1)) and estimates of (CO2)-C-14 yield (P-0) as,veil a s actual total yields of (CO2)-C-14. However, there was no relationshi p between K-d and second-stage zero order rates of mineralization (k(0 )). Microbial community characteristics (biomass and activity) were no t correlated with any of the mineralization kinetic parameters. Overal l, this study showed that environmental form had a profound effect on the ultimate fate of biodegradable chemicals in soil. This form is def ined by the physicochemical characteristics of the chemical, the compo sition and mineralogy of the soil, and the mode of entry of the chemic al into the soil environment.