The persistence of 28 common pesticides in raw river water was studied over an eight-week period. Twelve organochlorine, nine organophosphorus, and seven carbamate pesticides were studied at a concentration of 10 ^g/liter. No measurable degradation or chemical change was observed for the following organochlorine compounds: bhc, heptachlor epoxide, dieldrin, dde, ddt, ddd, and endrin. Azodrin was the only organophosphorus compound that was stable throughout the study. All carbamate compounds were significantly changed after one week, and all but Baygon were completely lost after eight weeks. Where possible, the degradation or chemical conversion products of the pesticides were identified.

Gas chromatography-mass spectrometry (GCIMS) data from several surveys pointed out the need for a standard procedure for calibration of the ion abundance scale in GC/MS systems. In addition, there is a need for a standard test to evaluate the overall performance of these systems. A number of proposed reference compounds were evaluated with respect to a set of criteria for an ideal GC/MS reference compound. The compound decafluorotriphenylphosphine (DFTPP) was selected because its propertles best satisfied the crlterla. A set of standard relative abundance ranges for DFTPP were developed by examination of GC/MS data obtained on a variety of systems. Computerized data systems were considered an integral part of the GC/MS system for both ion abundance calibrations and performance evaluations.

°Cdoes not destroy HNOg, however. The presence of up to x/2 mL of HNOg does not interfere with the fluorometric analysis of Se. The 2 • 01 in the stabilizing solution helps minimize oxidation of the DAN by HNOg (9). ACKNOWLEDGMENTThe authors thank D. Scherer and A. Jacobson for providing the tomato leaf sample and the value for its Se content obtained by using the HN03/HC104 digestion method.

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