Variability in captan residues in apples from a Canadian orchard.

Apple trees in an orchard in Quebec, Canada were treated, following label directions, with the fungicide captan (1,2,3,6-tetrahydro-N-(trichloromethylthio)phthalimide) during the 2003 agricultural season. A total of 142 apples from three rows of trees were selected for determination of captan by GC/MS. Individual apples were found to contain captan levels ranging from 16.9 to 6350 ng g-1. Only two individual apple samples exceeded the Canadian maximum residue limit (5000 ng g-1) for captan in apples. Six composite samples, comprising half portions of eight individual apples, were analysed from each of the three experimental rows. Composite samples ranged in concentration from 166 to 2620 ng g-1. The greatest uncertainty associated with the measured concentrations was due to variability among apples rather than the measurement of residue levels.

Organophosphate levels in apple composites and individual apples from a treated Canadian orchard.

Azinphos-methyl, phosalone, and phosmet were applied individually to separate rows of trees within a commercial apple orchard in Quebec, Canada, during the 2003 agricultural season. Apples were collected for residue analysis immediately prior to the harvesting of the remaining apples for market distribution and were prepared for analysis as both individual apples and as composites of eight individuals. Analysis of the three applied compounds, as well as five organophosphate insecticides that were not applied, was performed using gas chromatography-mass spectrometry. Azinphos-methyl, phosalone, and phosmet, which were applied, were detected in all samples analyzed at concentrations ranging from 0.004 ng/g to 2260 ng/g. Methidathion was not observed in any sample. Chlorpyrifos, diazinon, dimethoate, and malathion concentrations ranged from below method detection limits to 0.71 ng/g, and the detection frequency for these compounds ranged from 20% to 100%. Residues measured in this study were all below the Canadian maximum residue limit for apples. Variability factors ranged from 2 to 19 for all compounds observed in this study. Composite samples may not accurately reflect the extremes of exposure from consumption of single servings of apples.