Uptake of Malathion from Galvanized-Steel Surfaces by Stored Barley

Abstract

Columns of barley 4 cm deep were placed on galvanized-steel surfaces treated with malathion at 0.5 g (AI)/m2 and sampled at 0- to 1-, 1- to 2-, 2- to 3-, and 3- to 4-cm levels for 8 months at 22°C or under ambient western-Canadian storage conditions (−18 to 33°C). Insecticide residues were highest in the 0- to l-cm level for both storage environments; they increased from 6.62 ppm at 2 weeks to 53.09 ppm at 7 months at 22°C, and from 6.05 ppm at 2 weeks to 24.38 ppm at 8 months under ambient conditions. Malathion levels greater than 1 ppm were found in the 1- to 2-cm level only at 22°C during the first 7 months of storage. By 8 months, concentrations above 1 ppm were found in the 2- to 3-cm level at 22 and in the 1- to 2-cm level at ambient conditions. Although the moisture content (MC) of the seed was very low (8–9%) at 22°C, malathion movement was greater under these conditions than at the usually lower ambient temperature and higher MC (12–16%) because of vapor action of the insecticide. When bioassayed with adult Cryptolestes ferrugineus (Stephens), mortality was 100% at the 0- to l-cm level for both storage conditions. It rose from 24 to 98% at the 1- to 2-cm level during 2 to 8 months of storage at 22°C. The presence of malathion and the absence of its metabolite, malaoxon, were confirmed by combined gas chromatography-mass spectrometry. Malathion movement into stored barley was slight in this study, and would result in insect control at no more than 2 cm from steel surfaces treated with the recommended dosage of insecticide.