An In-transit Shipboard Fumigation of Corn1

Abstract

Bioassays showed that in-transit fumigation of corn in the holds of a bulk dry-cargo vessel with phosphine (derived from aluminum phosphide) or with the liquid fumigant 80–20 (a mixture of ca. 80% CCl4 and 20% CS2) were effective against stored-grain insects wherever adequate concentrations of fumigant were achieved and sustained. Although distribution of both fumigant gases was nonuniform, no exposed insects survived the fumigation with phosphine. In contrast, some insects on the surface of the corn and at the sides of the holds survived the treatment with 80–20. Highest concentrations of phosphine were sustained near the surface, and phosphine was slow to reach the bottom of the holds; the gases of the 80–20 fumigant permeated so rapidly to the bottom of the holds that high concentrations were sustained there but only low concentrations were found on or near the surface of the grain. Aeration (by opening the hatch covers) rapidly removed fumigant gases from the surface of the grain, but 10–11 days of aeration had no apparent effect on the concentrations of 80–20 fumigant at the bottom of the holds. Also, as the concentration of phosphine decreased near the surface during aeration, it increased at the bottom of the holds. None of the fumigant gases were detected in working areas or living quarters of the ship in transit, but during unloading, low levels of phosphide were occasionally detected on the surface of the grain and in the belt house of the unloading facility. Concentrations of CCl4 (and sometimes of CS2) that exceeded the threshold limit values were detected on the surface of the grain and in the belt house. Residues of phosphine were highest on unaerated samples taken directly from the surface of the corn before unloading began, but these residues did not exceed 5.6 ppb. Residues of CCl4 and CS2 ranged from 5 to 123 ppm and from <0.3 to 2.7 ppm, respectively.