Comparison of Two Dosages of Hydrogen Phosphide for In-transit Fumigation of Wheat on a Bulk Dry-cargo Ship1

Abstract

Wheat aboard a bulk dry-cargo vessel was fumigated in transit with Detia Gas EX-B bag blankets at either 1.17 g (AI)/m3 or 1.94 g (AI)/m3. High concentrations of hydrogen phosphide gas were maintained in the holds (555–720 ppm at day 15.5). Gas penetrated the wheat mass slowly at both application rates, and did not reach equilibrium at 15.5 days. The vertical penetration rate appeared to be faster than the lateral rate. There was an apparent advantage to applying the higher rate. At 15.5 days, average gas concentrations at the bottom of holds treated at the higher rate were significantly higher than those at the bottom of holds treated at the lower rate. No live insects were recovered from wheat samples in the five fumigated holds except near the bottom of one. However, bioassays reflected complete control only in the partially filled hold. No hydrogen phosphide was detected in the crew’s living areas. Low gas concentrations were detected on deck near some main hatches during the first 4 days, but posed no danger to the crew. Pressure-vacuum readings recorded on holds ranged from +16 to −12 mm H2O. When hatches were opened at the destination, holds ventilated rapidly and gas concentrations within the grain mass decreased as unloading progressed. Hydrogen phosphide residues on samples of wheat taken at discharge were below the tolerance of 0.1 ppm, regardless of dosage applied or location of the sample in the wheat mass.