PubMed · 56967
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J R Brown, L Y Chow, C B Deng. 1976. The effect of Dursban upon fresh water phytoplankton.. https://doi.org/10.1007/bf01685068
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A study was undertaken to compare and evaluate the different types of 63Ni and 3H electron capture (ECD) and flame photometric detectors (FPD) as part of the Canadian Check Sample Program on Pesticide Residue Analysis. Twenty-seven laboratories were supplied with chlorpyrifos standard solutions for the determination of linear range and minimum detectable amounts (MDA). Each laboratory selected its own operating conditions except for the FPD study. Results for the FPD were compared with standardized flame conditions designed to optimize the exponential factor i, the S-mode. The MDA of the ECDs (pulsed and direct-current) ranged from 0.09 to 0.17 pg/sec for 63Ni and 3H sources respectively. The corresponding MDA for the linearized ECDs (pulse modulated or constant current) was 0.04 pg/sec and a linear range of 10(4) or greater with nitrogen as the carried gas. Use of argon/methane and a pulse width of 0.1 usec extended this range to 10(5) but the sensitivity was not as great as with nitrogen carrier gas. The practical limit of detector sensitivity was found to be instrument dependent depending primarily on the noise level. In the FPD study, operating in the P-mode gave an average MDA of 5.97 pg/sec and a linear range of 2 x 10(3). Similarly, the S-mode parameters were 81.1 pg/sec and 8 x 10(2) respectively with an average exponential factor of n 1.8. Attempts to apply optimized detector gas-flow conditions improved sensitivity and linearity in the S-mode only.
A simplified technique for assessing the effect of pesticides on non-target soil microorganisms was developed. Changes in microbial population determined by the dilution plate method, in nitrification by the soil perfusion technique, and in oxygen consumption using a differential respirometer are the only measurements required. A comparison of the effects observed for three pesticides, dieldrin, chlorpyrifos and Vorlex, in three soil types with those produced by an antibiotic, a fungicide, a nitrification inhibitor and steam pasteurization of the soil clearly demonstrate the effectiveness of the simple technique.
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