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Phosphine As A FumigantPhosphine is a simple molecule that consists of a single phosphorus atom and three hydrogen atoms, PH3. Phosphine is a gas at standard temperature and pressure and has a density very close to that of air. Phosphine is also highly toxic to organisms undergoing oxidative respiration, but is non toxic to organisms kept under low oxygen (<1%) or that can anaerobically respire (i.e. ferment). Because of these characteristics, phosphine is widely used as a fumigant of metabolically dormant stored products such as grain. The toxicity of phosphine kills insect pests that might infest the grain, but does not affect the viability of the dormant grain. Because continued use of the previously widely used fumigant methyl bromide has been curtailed under the Kyoto Protocol, phosphine is the only widely used, cost effective, rapidly acting fumigant that does not leave residues on the stored product. Given the heavy reliance on phosphine as a means of protecting grain from insect infestation, it is disturbing to note that high levels of resistance toward phosphine have become commonplace in many countries of Asia and in Australia as well. Active research in Australia into the mode of action of phospine and the mechanisms whereby insects acquire resistance is being carried out by the CSIRO in Canberra, QDPI&F in Queensland and the University of Queensland.
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