Assessment of bioavailability using a multicolumn system

The bioavailability of sorbed naphthalene was studied with a surface soil u sing a multiple soil column system. This approach allowed monitoring contam inant concentrations in both the liquid and soil phases. Biodegradation and desorption parameters were determined in independent column experiments. A model in which desorption and biodegradation occur as sequential and indep endent processes successfully described the concentration of naphthalene in bath phases. This result indicates that this organism only utilized liquid -phase contaminant, and direct soil-phase degradation did not occur. A prev ious study using the same organism concluded that direct soil-phase degrada tion occurred on four different soils in completely mixed batch systems. Th e discrepancy between these reports appears to be caused by the different c onditions existing in batch and column systems and the use of mineralizatio n data to infer desorption rates in the earlier study. We conclude that if substrate depletion and mineralization rates are different, then desorption must be described using substrate concentration data from both the liquid and solid phases.