QUANTITATIVE SEPARATION AND DETERMINATION OF INORGANIC AND ORGANIC FORMS OF TOTAL CARBON AND RADIOCARBON IN NATURAL-WATERS AND APPLICATION AT A RADIOACTIVE-WASTE MANAGEMENT SITE

A method for the quantitative separation and measurement of both total carbon and C-14 in dissolved inorganic carbon (DIC) and dissolved org anic carbon (DOC) in moderate-volume (up to 1.51) samples is presented , accompanied by a systematic optimization of process and analytical v ariables. Inorganic carbon is removed by acidification and gas strippi ng, while DOC is wet-oxidized using a mixture of potassium persulphate , potassium dichromate, and perchloric acid and an oxygen sweep while boiling the sample. This treatment is shown to provide quantitative ox idation of even refractory compounds (humic acid) at concentrations ab ove those observed in natural waters. In both cases, the CO2 is trappe d in NaOH, precipitated as BaCO3, and subsequently re-converted to CO2 and transferred to Carbo-Sorb for liquid scintillation counting. The study analyzed the effects of CO2 loading, storage time, and Carbo-sor b/Permafluor E(+) ratios on quenching, sensitivity and efficiency in C -14 measurements. The high precision and accuracy (each +/-5%), and lo w detection limits (0.1 and 0.3 mg.l(-1) for DIC and DOC, respectively and 0.06 Bq.g(-1) of carbon for C-14) provided by the method make it suitable for radiocarbon speciation studies in natural waters. The met hod has been applied to measure radiocarbon concentrations in ground a nd surface waters downgradient of a low level radioactive waste manage ment site at the Chalk River Laboratories. Radiocarbon releases from t he waste to groundwater occur in both inorganic and organic forms. App roximately 20% of the total carbon and 10% of the total C-14 in ground water are present in organic species; less than 2% of both the (DIC)-C -14 and (DOC)-C-14 delivered to the wetland by groundwater discharge s ubsequently leave in surface waters.