THE FATE OF CHLORPYRIFOS-METHYL IN STORED WHEAT - A COMPARISON OF A LABORATORY-SCALE EXPERIMENT WITH A PILOT-SCALE TREATMENT

An experiment was carried out in which a pilot‐scale treatment of a bulk of grain with chlorpyrifos‐methyl was compared with a laboratory treatment of 1 kilogram of grain with 14C‐radio‐labelled chlorpyrifos‐methyl. The conditions under which the grain was maintained in the laboratory resembled those of the pilot‐scale treatment as closely as possible, with sampling and analysis being carried out at the same time and in a similar manner in both. The results from the two experiments were in general agreement with approximately 60% of the chlorpyrifos‐methyl remaining intact at the end. A satisfactory level of insect control was achieved in the pilot‐scale treatment although it was not possible to assess efficacy in the radiochemical experiment. The use of the radio‐label enabled more information about the fate of the degraded insecticide to be obtained from the laboratory experiment. The majority of this radioactivity comprised a fraction which remained within the grain tissue after solvent extraction. The level of activity in the grain tissues gradually increased with time but its nature is as yet unknown. The good agreement obtained between the residue profile and the breakdown patterns in both experiments would suggest that such a laboratory‐scale experiment can be a satisfactory model for the situation obtaining in a larger‐scale treatment. Copyright © 1990 John Wiley & Sons, Ltd