Potential underestimation of mineralization in (14)carbon-organochlorine biodegradation studies

Two methods are described for capturing C-14-carbon dioxide ((CO2)-C-14) fr om an alkaline clay soil in a study to determine the extent of mineralizati on of the chlorinated insecticide, endosulfan. In the first method, glass v ials containing an aqueous alkaline solution [2 M sodium hydroxide (NaOH)] were incubated within soil microcosms and the (CO2)-C-14 evolved and absorb ed (into the alkaline solution), was determined directly. This simple and c ommonly used method, routinely reported in the literature, has been shown i n the current study to be efficient and selective in absorbing (CO2)-C-14, even at high concentrations of applied C-14-substrate. A second method has been described for the recovery of indirectly evolved (CO2)-C-14 i.e., diss olved (CO2)-C-14 from the soil solution and (CO2)-C-14 fixed in the soil as carbonate(s) and is designed for use as a check for the presence of these forms of (CO2)-C-14. In the biodegradation trial in this study, very small amounts (<5%) of the originally applied C-14-endosulfan I were shown to be converted to CO2 over the trial period. It is recommended that during the d esign stage of establishing a biodegradation study, incubation conditions s hould allow for the capture all forms of (CO2)-C-14 to avoid underestimatin g the areal extent of C-14-substrate mineralization.