RESUMEN
An international interlaboratory study was conducted to determine the performance of a group of laboratories from developing and developed countries. The study used a commercial microwell ELISA on unknown samples spiked with different levels of DDT. The study design was based on Youden pairs and balanced replicates. Two soils, differing in particle size distributions, organic matter content, and cation-exchange capacities and thought to be DDT-free, were spiked at 5 DDT levels between 0.025 and 2 mg/kg. Nineteen laboratories in 17 countries took part in the collaborative trial; of these, the majority were modestly equipped laboratories in developing countries. Samples were analyzed without filtration or cleanup and using standards of pure DDT in methanol. Data were analyzed for repeatability and reproducibility, and average recoveries at the spike levels were calculated. Mean real recoveries for both soils were similar (103% for soil A and 100% for soil B), with values between 0.1 and 2 mg/kg DDT. Precision estimates were best in the linear working range of the assay (0.1-0.5 mg/kg DDT), with reproducibility relative standard deviations (RSDR) typically averaging about 38 and 46% near the upper and lower detection limits, respectively. Corresponding repeatability relative standard deviation (RSDr) values were 20-36% and 36-57%. Thus, even though much of the trial was performed under developing country conditions, performance statistics were similar to other reported results obtained with ELISAs on small molecules of agricultural importance, such as mycotoxins and pesticide and antibiotic residues.
Asunto(s)
DDT/análisis , Insecticidas/análisis , Residuos de Plaguicidas/análisis , Contaminantes del Suelo/análisis , Ensayo de Inmunoadsorción Enzimática , Estándares de ReferenciaRESUMEN
Toxicity of C14-ring-methyl parathion in penetration, tissue absorption, and metabolism by susceptible Helicoverpa armigera (Hübner) and Helicoverpa punctigera (Wallengren) larvae was compared. C14 methyl parathion penetrated the cuticle of H. punctigera more rapidly than of H. armigera, leading to initially higher internal insecticide concentrations in H. punctigera. The same methyl-parathion metabolites were recovered from H. armigera and H. punctigera. However, larger quantities of methyl paraoxon and p-nitrophenol-glucoside were extracted from H. punctigera. These results are discussed in terms of the history of insecticide resistance in H. punctigera and H. armigera in Australia.
Asunto(s)
Insecticidas/farmacocinética , Lepidópteros/metabolismo , Metil Paratión/farmacocinética , Absorción , Animales , Australia , Radioisótopos de Carbono , Resistencia a los Insecticidas , Insecticidas/metabolismo , Metil Paratión/metabolismo , Distribución TisularRESUMEN
An automated procedure is described for the rapid determination of the residual herbicide atrazine at ppb levels in soil-water extracts. The system consists of an autosampler connected to a C18 precolumn linked via a switching valve to a C18 analytical column and spectrophotometer. Peak height is superior to peak area for quantifying results with coefficients of variation of 0.48% and 0.89%, respectively, for 7.5 ng standard injections. Precolumn concentration eliminates the need for sample cleanup and achieves up to a 37% increase in peak height compared to an isocratic system. In a black earth soil, atrazine is identified as the principal phytotoxic constituent. The minimum detectable level is one-tenth the critical no-effect threshold for wheat. The method is well suited for predicting possible atrazine injury to susceptible crops and the measurement of other nonpolar analytes in aqueous solution.