Potential underestimation of mineralization in14carbon‐organochlorine biodegradation studies

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