U.S.EPA
Methyl Bromide Alternative Case Study
Part of EPA 430-R-97-030, 10 Case Studies, Volume 3
September 1997
This is an update of a July 1995 EPA report (Alternatives to Methyl
Bromide, Ten Case Studies) entitled "Structural Fumigation Using a
Combined Treatment of Phosphine, Heat, and Carbon Dioxide".
Considerable work has been done since that report with regard to the
described pest control method, as well as two other methods which also use
significantly reduced amounts of phosphine combined with carbon dioxide.
This report presents these methods as viable alternatives to the use of
methyl bromide in appropriate treatment situations.
Currently seven percent of domestic methyl bromide consumption is for
commodity and quarantine fumigation (Anonymous 1994b). Phosphine, another
fumigant gas, has been used successfully to control insects in a number of
plant and animal commodities (especially stored products), and therefore
can be a viable alternative to methyl bromide treatments. Compared to
methyl bromide, phosphine treatments can be more economical and easier to
use in some situations . When used correctly, phosphine can have a broader
spectrum of activity, penetrate more effectively and deeper into commodity
storages (thus reducing the number of fumigations required and the amount
of shut down time needed to perform the fumigation) and can exceed the 95
percent minimum kill rate required for methyl bromide fumigations (Sloane
Group 1996).
Existing phosphine formulations available on the market include air-tight
packages of pellets, tablets and plates (sachets) which contain and inert
ingredients. Once the package is opened, the metallic phosphides contacts
with moisture in the air, and phosphine gas is slowly produced. The
metallic phosphides most commonly used include: magnesium phosphide (used
primarily in the United States because it is safer and releases phosphine
faster than other phosphine compounds), calcium phosphide, and aluminum
phosphide (primarily used in Canada) (PhosphumeTM 1996, AAC 1996, Sloane
Group 1996). During conventional phosphine commodity treatments,
structures are first sealed and then the solid fumigant is placed in the
container or structure in several places to assure complete gas
dispersion. Phosphine levels reach the desired concentration in 3 to 10
days to achieve the proper effect. Following treatment, the structure is
aerated and the inert ingredient residue disposed of properly (Kelley
1997).
Although conventional phosphine treatments are convenient to use, there
are use limitations as a commodity treatment. For example, conventional
phosphine treatments can take up to two days to reach required
concentrations, leave residual dust after the treatment, and can be
corrosive to precious metals or alloys (i.e., copper, brass, gold,
silver). There are also health and safety concerns associated with
handling products that emit phosphine when exposed to the air (sometimes
at flammable concentrations leading to unexpected fires and possible
explosions) (PhosphumeTM 1996, AAC 1996, Kelley 1997, Sloane Group 1996).
Because of these disadvantages to conventional phosphine treatments,
recently improved phosphine treatment methods: such as the combination
method (using heat, phosphine, and carbon dioxide); the cylinderized
phosphine gas ECO2FUME; and the TURBO HORN (phosphine) GENERATOR, may be
more appealing alternatives to methyl bromide treatments in the future. A
more detailed description of these treatment techniques is presented
below.
Phosphine Treatment Techniques
COMBINATION TREATMENT
Combining heat, phosphine, and carbon dioxide as a commodity treatment
technique was first tested in 1992 and refined and patented by David
Mueller of Fumigation Service & Supply Inc. (FSS) in Indianapolis.
Since then researchers in the United States at Purdue University and
Oklahoma State University, and in Canada, South America, and Europe have
demonstrated the effectiveness of combination treatments as a pest control
method in flour mills (e.g., Hawaiian Flour Mill in Honolulu and the
Quaker Oats Company of Canada Limited), food processing plants, and
museums (Anonymous 1994a, AAC 1996, McCarthy 1996). The combined treatment
consists of 50 to 100 ppm phosphine (9 to 18 percent of the standard
phosphine concentration), heat (89.6-98.6 F, 32-37 C), combined with 4 to
6 percent carbon dioxide. Using low concentrations of phosphine reduces
the chance of corrosion of metallic materials at facilities, a common
problem associated with conventional phosphine treatment techniques.
Furthermore, heat and carbon dioxide help reduce moisture, thereby
limiting corrosion. The process relies on heat and carbon dioxide to
increase the susceptibility of pests to phosphine by interfering with
insect metabolism (i.e, by dilating insect spiracles, increasing
respiration and interfering with cellular energy cycles). This stress on
the insect allows for low levels of phosphine to more effectively kill all
insect life stages, including the egg stage (Anonymous 1994a, Mueller
1994a). Experiments have shown that combined treatments can produce 100
percent mortality within 24 hours or less for the egg, larvae, pupae, and
adult stages of stored-product insects, including the Angoumois grain
moth, red flour beetle, warehouse beetle, and rice weevil (Mueller 1994b).
Over the last five years, more than 40 successful combination fumigations
have been performed. Twenty-four of these have been for flour mills,
resulting in use reductions of over 100,000 lbs. of methyl bromide
(Mueller 1994b, Mueller 1994c, Mueller 1996a). This patented process is
less expensive than heat, more practical than carbon dioxide, and safer
and more effective than phosphine alone (AAC 1996, Mueller 1994c). As a
result, the combination technique shows promise as a replacement for
methyl bromide in flour mills and food processing facilities (Anonymous
1994a).
ECO2FUME
BOC Gases Group has developed and patented ECO2FUME, a gaseous phosphine
fumigation mixture that can be used as an alternative to in-situ
generation of phosphine from metallic phosphides. It consists of 2.6
percent by volume of phosphine in carbon dioxide premixed in a cylinder
and can be used on a wide variety of products, including foods, tobacco,
timber and cane products, buildings, and other structures (PhosphumeTM
1996, Carmi et al. 1995, Sloane Group 1996).
Eco2Fume appears to offer many advantages over other phosphine fumigation
techniques, including improved health and worker safety, environmental
benefits, and product quality (Ryan 1991, PhosphumeTM 1996, Carmi et al.
1995, Sloane Group 1996). Since Eco2Fume is premixed and ready to use, the
need for on-site mixing is eliminated. The gas is dispensed directly from
the cylinder into a sealed structure to be fumigated. The technique
achieves the required concentration in a matter of hours, allowing for
greater and more immediate control of phosphine concentrations during the
entire fumigation period. Because the gas is dispersed quickly and reaches
the desired concentration in a short period of time, the treatment itself
is shorter, and may result in less frequent fumigations, thus reducing the
risk of corrosion. The treatment prevents incomplete or variable phosphine
generation (such as that acquired with the use of metallic phosphides),
eliminates the need for disposal of residual product, and reduces worker
exposure.
As of the date of this publication, Eco2Fume does not have a label which
allows use as a commodity or quarantine treatment technique in the United
States. However researchers are collecting data and developing the
necessary information to meet regulatory requirements. Studies are also
being conducted on the use of Eco2Fume in quarantine situations (e.g.
pre-shipment, pre-marketing fumigations). Furthermore, BOC has initiated
plans for plant production and sourcing of phosphine. The registration
process to receive use labels has been initiated in the U.S., Canada,
Europe, and other parts of the world. The product is expected to be
available on the global market by the end of 1997, registered as Eco2Fume
in the U.S. and Canada, and PhosfumeTM in Australia and Europe (Mueller
1996b, Anonymous 1997).
Although Eco2Fume has not been used extensively in the United States,
over 9 million metric tons of grain are fumigated in Australia each year
using the PhosfumeTM process (Sloane Group 1996, Anonymous 1997). Eco2Fume
also has proven to be highly effective and beneficial to the cut flower
industry (MacDonald and Mills 1995), and as a result, this pest control
tool has good potential to be a viable substitute for methyl bromide in
this and other commodity fumigation applications (Mueller 1996b, Kelley
1997, Carmi et al. 1995).
TURBO HORN GENERATOR
A new method of generating phosphine gas, the Turbo Horn Generator
(manufactured by Fosfoquim S.A. in Santiago, Chile) has been developed,
field tested, and patented by Degesch de Chile. The method involves an
apparatus that rapidly produces phosphine on site when magnesium phosphide
granules (a new product) are placed in the unit with water, producing
hydrogen phosphide under controlled conditions. The gas is then mixed in
the apparatus with air and carbon dioxide until hydrogen phosphide
concentrations reach approximately 2.5 percent. The gas then is pumped
directly into the structure to be fumigated, while air is drawn from the
structure and recirculated through the system to maintain a constant
pressure and distribution. The system quickly produces large amounts of
gas from a relatively small amount of reactants and can quickly be
reloaded to produce more gas if necessary. Residues or any remaining
reaction products remain in the apparatus and can easily be disposed of
following treatment. Lastly, the generator is computerized to operate
automatically or manually and will stop automatically if any irregularity
or technical problems occur (Fosfoquim S.A. and Degesch De Chile Ltda
1996).
Advantages of the Turbo Horn Generator include a flexible system where
gas concentrations can be adjusted at any time during the fumigation, and
allows gas generation under various temperatures and humidities.
Furthermore, the system is easy to use and cost effective. This technique
has already been successfully utilized in several flour mills, granaries,
and silos (Fosfoquim S.A. and Degesch De Chile Ltda. 1996).
Costs
In general, the cost of phosphine treatments are only slightly higher
than those using methyl bromide. This is attributed to the fact that
phosphine treatments require marginally more equipment, labor, and
technical expertise than methyl bromide treatments (Table 1). However,
phosphine treatment costs are expected to decrease in the future as new
advances in phosphine gas generation technology are made. For example,
after initial capital costs, the Turbo Horn Generator is less expensive
than conventional phosphine treatment techniques. Furthermore, because
much of the cost for conventional fumigations is that associated with the
facility shutdown time necessary to complete disinfestation, phosphine
treatments, when correctly applied, are cost effective because they can
require a shorter shutdown than required for methyl bromide treatments
(Mueller 1994c).
Table 1. Comparison of Phosphine and Methyl Bromide Treatment Costs
($ per 1,000 cubic feet)
| Cost Factor | Methyl Bromide | TURBO HORN Generator | ECO2FUME | Combination Treatment | Aluminum Phosphide Tablets | Magnesium Phosphide Plates |
| Labor | $4.25 | $4.50 | NA | $4.50 | $4.75 | $5.10 |
| Equipment | $0.25 | $0.75 | NA | $1.25 | --- | --- |
| Chemical | $1.15 | $1.00 | NA | $1.50 | $2.00 | $4.50 |
| Additional | $1.75 | $1.85 | NA | $2.00 | $1.50 | $1.50 |
| TOTAL | $7.40 | $8.15 | NA | $9.25 | $8.25 | $11.10 |
Notes: NA = not available at this time.
Source: Mueller 1994c, Sullivan 1997.
References
Anonymous. ECO2FUME: a new fumigant. Fumigants & Pheromones 1997, No.
41, 1-2.
Anonymous. Methyl bromide phase-out. Fumigants & Pheromones 1994a,
No. 34, 4-5.
Anonymous. Montreal Protocol on Substances that Deplete the Ozone Layer;
Methyl Bromide Technical Options Committee (MBTOC), 1995 Assessment.
United Nations Environment Programme, 1994b; EPA 430/K94/029.
Agriculture and Agri-Food Canada (AAC). "Heat, Phosphine, and CO2
Collaborative Experimental Structural Fumigation"; report to the
Canadian Leadership in the Development of Methyl Bromide Alternatives;
Ottawa, Canada, 1996.
Carmi, Y.; Kostjukovsky, M.; Binenboim, I.; Golani, Y.; Frandji, H.
Presented at the 1996 Annual International Research Conference on Methyl
Bromide Alternatives and Emissions Reductions, Orlando, FL, November 1996;
paper 76.
Fosfoquim S.A. and Degesch De Chile Ltda., Santiago, Chile, unpublished
results, 1996.
Kelley, P., Fumigation Service & Supply, Inc., unpublished results,
1997.
Macdonald, O.C.; Mills, K.A. Presented at the 1995 Annual International
Research Conference on Methyl Bromide Alternatives and Emissions
Reductions, San Diego, CA, November 1995; paper 95.
McCarthy, B. Presented at the 1996 Annual International Research
Conference on Methyl Bromide Alternatives and Emissions Reductions,
Orlando, FL, November 1996; paper 60.
Mueller, D.K., Fumigation Services & Supply, Indianapolis, IN,
personal communication, 1994c.
Mueller, D.K. In Stored Product Protection: Proceedings of the 6th
International Working Conference on Stored-product Protection. Volume I;
Highley, E.; Wright, E.J.; Banks, H.J.; Champ, B.R., Eds.; Canberra,
Australia, 1994b; paper 55.
Mueller, D.K. Methyl bromide alternative update. Fumigants &
Pheromones 1994a, No. 34, p 2.
Mueller, D.K. Presented at the 1996 Annual International Research
Conference on Methyl Bromide Alternatives and Emissions Reductions,
Orlando, FL, November 1996a; paper 68.
Mueller, D.K. Presented at the 1996 Annual International Research
Conference on Methyl Bromide Alternatives and Emissions Reductions,
Orlando, FL, November 1996b; paper 75.
PhosphumeTM. BOC Gases Label, HOR020116, MSVAUS, 1195, 10k, BOC Gases
Australia Limited, Chatswood, New South Wales, 1996.
Ryan, R.F. Presented at the Australian Institute of Food Science and
Technology 24th Annual Convention, Hobart, Australia, July, 1991.
Slone Group, The. "ECO2FUME: Executive Summary. ECO2FUME Tolerance
Data"; Report by the Slone Group: Greenwich, CT, 1996.
Sullivan, J.B., Sullivan and Associates, Inc., Harrisonburg, VA, personal
communication, 1997.
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