The influence of plastic consumer packaging for polished rice on phosphine gas penetration, desorption, and residue.

摘要

Phosphine fumigation of polished rice within polyethylene consumer packaging was carried out, and the effects of plastic film on gas penetration into the package, gas desorption from the package, and phosphine residue on fumigated polished rice were investigated. 100% mortality was obtained for the Tribolium confusum adults and Plodia interpunctella larvae that were inserted into the center of the package containing 2 kg of rice that was then fumigated with PH₃ at 0.82 g/m3 for 72 hours at 15 degrees C. A certain amount of phosphine gas that can completely kill test insects should be able to penetrate into the center of consumer packaging through polyethylene film. As for gas desorption, gas concentrations inside packages without ventilation holes remained higher than packaging with 14 holes. Gas concentrations inside packages without holes were from 519 ppm at 10 minutes through 59 ppm at 72 hours after forced exhaust was completed. For the package with 14 holes, detected concentration was rapidly decreased to ca. 20 ppm at the 24-hour point, and after the 48-hour point all values were indicated below 1 ppm. Rice in packages identical to those used in the desorption study were also analyzed for phosphine residue by headspace gas chromatography. Actual levels of residue in the package without holes were from 0.0011 to 0.0014 ppm, not prominently higher values compared to residues acquired in analysis of the package with 14 holes, which were detected from 0.0009 to 0.0011 ppm; therefore, it is considered that ventilation holes are not a main factor impacting residue levels. Regardless of the number of holes in a package, all residues were indicated at a much lower level than the maximum residue limits (MRL), set at 0.1 ppm for rice in Japan. Longer-term aeration should be recommended to expedite gas desorption from rice packages to ensure worker safety.