Development of sulphuryl fluoride as a fumigant for the milling industry

Abstract

The potential of sulphuryl fluoride as a fumigant to replace methyl bromide as a treatment for the disinfestation of flour mills was investigated. The effectiveness of the gas in penetrating flour was compared with methyl bromide and found to be 10 times as rapid. No significant effect on penetration time was observed between test runs at 18 - 28oC. Sorption levels on flour were less than one tenth that for methyl bromide under similar conditions and gas aired off rapidly after exposure. Baking tests on whole meal flour treated with different dosages of sulphuryl fluoride revealed no differences between control and treated flour samples, though the quality of bread from the insecticide-free organic flour variety used in the trials was uniformly low. Studies of the vulnerability of materials used in the electronics industry to corrosion or reaction with sulphuryl fluoride revealed no ill effects from exposure in the absence of free water. A computer exposed to gas at temperatures up to 60o C and at a dosage equivalent to about 15 practical mill fumigations was able to operate normally after exposure.

The efficacy of sulphuryl fluoride was assessed against seven pest species of flour and flour mills, Cryptolestes turcicus, Gnatocerus cornutus, Ptinus tectus, Sitophilus granarius, Tenebrio molitor, Liposcelis bostrychophila and Acarus siroat 25oC, and on eggs of several of these species at 30oC. Eggs of the tenebrionid beetles G. cornutus and T. molitor, and all stages of the flour mite A. siro, were highly tolerant. An examination of egg hatch times after treatment revealed strong evidence that, as with the fumigant phosphine, eggs continue their development while under gas. Efficacy of treatment of eggs was significantly enhanced by increasing the temperature from 25 to 30oC and complete control of eggs of most species was obtained by a concentration time product of 1000 g h m-3 at 25oC and about 700-800 g h m-3 at 30o C.

In field trials, the ability to dose and maintain effective concentrations in flour mill structures was demonstrated but additional heating was required to avoid the use of excessive amounts of gas. For all trials this was provided by the use of external positive pressure heated air sources, supplemented in one trial by internally placed 18 kW convectional air heaters used for thermal mill disinfestation treatments in Germany . In all cases the heating was stopped just prior to dosing and temperatures therefore fell during the fumigation. The highest temperatures were achieved in the last trial, which was conducted during a spell of unusually warm weather. The trials demonstrated the potential of fumigation with sulphuryl fluoride as a successful whole-site disinfestation treatment to replace methyl bromide.