Methyl Bromide Replacement 

PROPYLENE OXIDE

THE REGISTERED FUMIGANT, THE PROVEN INSECTICIDE

As A Methyl Bromide Alternative

By Tom Griffith and Morris Warren, ABERCO, Inc.

This report is an attempt to demonstrate that the use of the New Old Fumigant, Propylene Oxide, can replace methyl bromide (MeBr) in many applications. With 40 years of food use history, we expect propylene oxide will satisfy all the tests of availability, effectiveness, safety, and practicality.

ABERCO, Inc. has held an EPA registration since 1984 and is now the sole registrant for the use of propylene oxide for fumigation purposes. ABERCO's U.S. EPA approved label reads "to aid in the control of microbial spoilage and as an insecticidal fumigant for the control of stored product insects, To reduce bacterial and mold contamination in processed spices, cocoa and processed nutmeats (except peanuts)."

AVAILABILITY

Worldwide over ten billion pounds of propylene oxide are produce annually. Propylene oxide is a basic chemical intermediate used to produce a wide variety of products such as urethane foams, cosmetics, polymers, modified starches, gums, food emulsifiers and of course propylene glycol, the GRAS (Generally Regarded as Safe) food additive. Propylene glycol is also the basis for the nontoxic Sierra antifreeze. The hydrolysis of propylene oxide to propylene glycol will be explored later.

EFFECTIVENESS

The effectiveness of propylene oxide against bacteria in nuts, cocoa, and spices has been well documented. Our customers routinely treat their products with propylene oxide to reduce molds and yeast as well. Many of ABERCO's customers in these industries use MeBr to control stored product insects. However, with the accelerated timetable for banning all production and importation of MeBr, our top priority was to demonstrate the effectiveness of propylene oxide to kill insects found in cocoa beans, inshell nuts and spices. This study is underway at the Dried Fruit Association of California and the early results indicate that propylene oxide, at doses similar to the MeBr dose, kills all stages of the Confused Flour, Warehouse, Red Flour, and Cigarette Beetles along with the Indian Meal Moth. Propylene Oxide is particularly effective on eggs. A study of the rate of kill of the Coding Moth larvae in walnuts, as well as, off gassing studies on Raisins, Prunes and Figs are scheduled.

FOOD SAFETY AND ENVIRONMENTAL IMPACT

The allowable residue tolerance for propylene oxide is 300 ppm, however these residues are not persistent as they will evaporate rapidly from the substrate due to the relatively high vapor pressure. Furthermore, propylene oxide will react in the human stomach to form (GRAS) Propylene Glycol. ABERCO designed a research program utilizing radio labeled propylene oxide for 100% accuracy and irrefutability. The tests were conducted in two parts:

  1. Using simulated stomach juice at pH 1.0, the PPO half life was 63 seconds.
  2. Using human stomach juice at pH 1.5, the PPO half life was 83 seconds.
Notes:
  1. All PPO converted to (GRAS) Propylene Glycol.
  2. No propylene chlorohydrin, a suspected byproduct, was found.
  3. These facts indicate that propylene oxide is not likely to be carcinogenic of harmful.
The conversion of Propylene Oxide to Propylene Glycol is catalyzed by both acid and base and the rate of the reaction is determined by the concentration of the catalyst. This is also why Propylene Oxide will hydrolyze to Propylene Glycol in the soil. Both Propylene Oxide and Propylene Glycol are biodegradable.

PRACTICALITY

The initial fumigation work shown above was done with flammable 100% PPO in vacuum chambers at ~80 deg.F for 4 hours @ 100mm Hg according to our label. Note, it is very important not to confuse Propylene Oxide with Ethylene Oxide because their structure is similar. Ethylene Oxide may not be used on food products since it is a known carcinogen, whose byproducts are also toxic. Furthermore, it is explosive from 1% to 100% in air. Propylene Oxide, on the other hand is flammable from 3% to 37% in air, much like propane. Since many of the new uses contemplated will be better served by a non flammable insecticide, ABERCO will be working with the USDA at Fresno to determine the efficacy of a nonflammable mix of 8% PPO and 92% CO2 under atmospheric conditions. This mixture is currently on ABERCO's label. There is a history of using this mix at ambient atmospheric conditions in stack and structural fumigation, but the insecticidal efficacy data on the commodities in question needs to be confirmed. Delivery systems for this gas mixture can be tailored for the application. The inhalation limits for 100% Propylene Oxide are: OSHA 100 ppm twa. EPA: 20 ppm Worker safety issues are easily handled by the most basic precautions.

AFLATOXIN

Researchers at the University of Tennessee have determined that MeBr is 92.8% effective against A. flavus and A. parciticus, the molds required for the production of Aflatoxin. Phosphine, however is reported to be only 7.% effective at the same dose. Since Propylene Oxide is widely used to reduce mold and yeast in nutmeats and spices, ABERCO, Inc. has commissioned the Dried Fruit Association of Ca. to determine the efficacy of propylene oxide against these two molds. The control of the target insects and these molds in the post-harvest environment will reduce the formation of Aflatoxin in the commodity. This dual function will offer another portion of the advantages obtained by using MeBr.

PREPLANT

There are references indicating that Propylene Oxide is a Nematicide that is effective against both egg masses and larvae of M. hapla in soil. Propylene Oxide has been reported to be highly mobile in soil and has physical characteristics that appear to be ideal for soil fumigation. Certainly, its biodegradability and its conversion to nontoxic biodegradable Propylene Glycol in ground water answer some of the key environmental questions. ABERCO, Inc. is planning some preliminary studies in this area.

CONCLUSIONS

Propylene Oxide is already approved for use on food products and it passes the key tests of availability, effectiveness, safety, and practicality. Although more information is needed to confirm efficiency, it is readily apparent that Propylene Oxide is an important, viable contender for replacing MeBr in some critical applications.

For more information about PPO as a MeBr replacement, see also News Releases, Research and Tellitgrams(c).

[Home] [Propylene_Oxide] [News_Releases] [Tellitgrams(c)] [Research] [Contact_Information] [Company_Profile] [Help]