Article on containerized phosphine disputed

by Emily Wilson
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We read with interest the article "Eco-Friendly Fumigant" (see World Grain, February 2001, page 33). We believe that Cytec's Eco2Fume system will be a useful addition to the arsenal of phosphine fumigation techniques. However, this article contains a number of misstatements, some regarding metal phosphide fumigants.

The article refers to "toxic phosphide residues left over from tablets." The LD50 of spent residual dust from Phostoxin (a Degesch brand name) is 3,000 mg/kg, slightly less toxic than table salt. The toxicity of spent magnesium phosphide products is even lower. To the best of our knowledge, an incident involving poisoning from spent dust has never been reported.

A more serious misstatement is the assertion that metal phosphide products release more phosphine than Eco2Fume to the atmosphere during the course of a fumigation. We believe this to be grossly inaccurate.

When similar dosage rates are used, metal phosphide fumigation will produce much lower volumes of gas than Eco2Fume, thereby releasing much smaller volumes of phosphine-laden air into the air around the structure under treatment. For example, assuming a dosage rate of 50g PH3 per 1,000 cu.ft., Eco2Fume will inject 50g of phosphine and 2,450g of carbon dioxide into each 1,000 cu.ft. of the structure. This equates to a total volume of almost 5% of the storage volume. By comparison, Phostoxin liberates gases which total less than 0.2% of the storage volume.

Of the gases produced by the Phostoxin formulation, only about 24g of carbon dioxide would be added to each 1,000 cu.ft. of the storage, and ultimately be discharged to the atmosphere. This is less than 1% of that discharged by Eco2Fume.

Since carbon dioxide is believed to be an important contributor to global warming, Degesch has been working for years to reduce emissions of this gas. Our efforts have been only partially successful in that several packaged products have been developed which liberate no gases other than phosphine. However, for safety reasons, we have not been able to reduce carbon dioxide emissions from our pelletized products, which are added directly to commodities. From the above discussions, it would seem reasonable to assert that metal phosphide fumigants are at least as "friendly" to the environment as Eco2Fume.

When applied according to label instructions, under conditions suitable for phosphine fumigations, metal phosphides will produce results equal to any other technique of which we are aware. Likewise, we are unaware of any dust explosions initiated by metal phosphide fumigants anywhere in the world.

This leads to our most critical remarks. According to a recent report from Australia, many insect species are surviving "flow-through" applications. Note that no resistance was reported when metal phosphides were the major source of phosphine for fumigation of stored commodities.

Prior to the report from Australia, there has never been an outbreak of widespread resistance to phosphine in developed countries. While resistance is a serious problem, no matter where it occurs, it can assume catastrophic proportions if the affected countries are major exporters of stored commodities, such as Australia and the United States.

Again, we feel that Eco2Fume and the technical staff at Cytec will be a welcome addition to our industry. However, there is no magical application technique for phosphine that will defy the laws of nature.

Donald G. Shaheen

Technical director, Degesch America, Inc.

Weyers Cave, Virginia, U.S.