U.S.EPA
Methyl Bromide Alternative Case Study
Part of EPA 430-R-96-021, 10 Case Studies, Volume 2
December 1996

Structural Fumigation Using Sulfuryl Fluoride: DowElanco's Vikane™ Gas Fumigant

Sulfuryl fluoride (SO2F2), also known as Vikane™ (99.8 percent by weight sulfuryl fluoride and 0.2 percent inerts), was developed by Dow Chemical in the late 1950s as a structural fumigant. Vikane™ (currently manufactured by DowElanco) possesses characteristics for the eradication of structure-infesting insects (Derrick et al. 1990). It is non-flammable, non-corrosive, and does not cause undesirable odors. It quickly penetrates structural materials, is effective against a variety of structural pests, and dissipates rapidly during aeration (Chambers and Millard 1995, Stewart 1957 and 1966, Kenaga 1957). This material is an established structural fumigant, and therefore is considered an alternative to methyl bromide. Since first marketed in the United States in 1961, it has been used to fumigate more than one million buildings, including museums, historic landmarks, rare book libraries, government archives, scientific and medical research laboratories, and food-handling facilities (DowElanco 1994). Compared to methyl bromide, sulfuryl fluoride penetrates structural materials more rapidly, and is effective against a wide variety of pests, and leaves less residue in materials after aeration. These characteristics make it a viable alternative to methyl bromide in structural fumigation (Derrick et al. 1990).

Sulfuryl fluoride is an excellent broad-spectrum fumigant, due to its toxicity to target pests, good dispersion and penetrating qualities. It is commonly used to control a wide variety of household pests, including drywood and Formosan termites (Bess and Ota 1960, Stewart 1957), wood-boring beetles (powder post beetles, death watch beetles, and old house borers), fabric and museum pests (clothes moths and furniture and carpet beetles), cockroaches, bed bugs, snails (Richardson and Roth 1965), brown dog ticks, and rodents (rats and mice) infesting buildings, furnishings, construction materials, and vehicles (DowElanco 1996a, Kenaga 1957, Bess and Ota 1960, Roth 1973).

Fumigant Qualities Compared with Methyl Bromide

In many ways, Vikane™ can be a preferred structural fumigant over the use of methyl bromide. Unlike methyl bromide, sulfuryl fluoride does not react with sulfur-containing materials to form off- or skunk-odors (DowElanco 1996a). Vikane™ passes through nylon and polyethylene sheeting much more slowly than does methyl bromide, so that the gas is easily confined by the plastic tarps commonly used in structural fumigation. Furthermore, sulfuryl fluoride penetrates into and aerates from wood much faster than methyl bromide (DowElanco 1996a, Bond 1984, Grey 1960). Rapid penetration of substrates inhabited by the pests allows for variable (shorter) exposure times compared with standard exposure times for methyl bromide (DowElanco 1996a). Lastly, because sulfuryl fluoride is about 20 times less soluble in water than methyl bromide (i.e., 0.075 percent by weight at 77 F (Meikle and Stewart 1962)), water can be used to form a barrier or bottom seal during the fumigation process (DowElanco 1996a).

Efficacy

Sulfuryl fluoride is highly toxic to all post-embryonic life stages of insects (UNEP 1994), eggs of most species are less susceptible (DowElanco 1996a; Bond 1984). The efficacy of sulfuryl fluoride depends on the concentration reaching the target pest and the duration of exposure. As a result, the dosage of sulfuryl fluoride required for a specific pest is calculated in "ounce-hours," ounces of Vikane™ multiplied by hours of exposure. In general, insect eggs require a higher ounce-hour dosage of sulfuryl fluoride compared to later life stages (i.e., a 10-fold increase in dosage for some insect species) (UNEP 1992, UNEP 1994). However, the ability to control egg stages of social insects (i.e., termites and ants) is not necessary because these newly hatched larvae cannot survive without adult care. Furthermore, the higher dosages required to control insect eggs can be obtained by increasing the exposure time, concentration of sulfuryl fluoride, or a combination of the two. Fumigators use a "fumiguide calculation system" to determine the amount of Vikane™ required for specific pest and fumigation conditions (DowElanco 1994 and 1996a).

Sulfuryl fluoride prevents insects from metabolizing the stored fats they need to maintain a sufficient source of energy for survival by disrupting the glycolysis cycle (Meikle et al. 1963). Mortality may be delayed for insects for several days following fumigation (Osbrink et al. 1987), therefore insects that have received a lethal exposure to sulfuryl fluoride may still be alive immediately following fumigation (no longer than 3 to 5 days for termites) (DowElanco 1994). Sulfuryl fluoride has also been demonstrated to reduce oxygen uptake in insect eggs (Outram 1970).

Usage

Vikane™, a restricted-use pesticide, is currently registered to control certain pests in the following infested sites: structures, fumigation chambers, construction materials and furnishings (including household effects), and all vehicles except aircraft and subsurface water vessels (Derrick et al. 1990, DowElanco 1996a). Vikane™ is odorless, colorless, non-flammable, non-reactive, and non-corrosive at temperatures normally encountered in structural and other fumigations. As a result, it can be used to fumigate photographic supplies, metals, paper, leather, rubbers, plastics, cloths, wallpapers, household furnishings, and a variety of other articles (Trinkley 1996, Derrick et al. 1990, Anonymous 1980). It has little or no effect on the germination of weed and crop seeds; however, it is injurious to green plants, vegetables, fruits, and tubers. Sulfuryl fluoride does not form toxic surface residues on household items, and thus dishes, cloths, and other items do not need to be removed or washed following fumigation with Vikane™ (DowElanco 1994). It is not registered for use where food and grain commodities are present because food residue tolerances have not been established. Guidelines for use of the fumigant specifically state that "under no conditions should Vikane™ be used on raw agricultural food commodities, foods, feeds, or medicinal products destined for human or animal consumption, or on living plants" (UNEP 1994, Bond 1984).

Application

To control termites, Vikane™ is applied to tarped or sealed structures for an exposure period of 2 to 72, commonly 20-24 hours (the duration depends on fumigant and labor cost considerations and time constraints), followed by a 6 to 8 hour aeration period (UNEP 1994). It is packaged in white cylinders as a liquid under pressure (99.8 percent Vikane™ with no other pesticides, solvents, or additives); however, it volatilizes rapidly upon release from the cylinder. Therefore, the gas is released under its own vapor pressure through tubing directly into the structure from pressurized cylinders. The released sulfuryl fluoride is dense (3.5 times heavier than air), and will extract heat from the air as it changes from a liquid to a gas. Fans are used not only to distribute Vikane™ throughout the fumigation area, but also to as heat exchangers to mix cool air near the fumigation introduction site with surrounding warmer air to prevent condensation of moisture from the air. Unlike methyl bromide, no auxiliary heat source is required (Stewart 1957).

As with methyl bromide, exposing sulfuryl fluoride to open flames can form acids which may react with metals, glass, ceramic tiles, or china near the heat source. Thus, prior to structural fumigation, all open flames and glowing heat filaments are turned off or disconnected (i.e., pilot lights, electric heater elements, or automatic switches) (DowElanco 1994, Derrick et al. 1990). Once the appropriate amount of Vikane™ is introduced, the fumigator closes the cylinder valve and removes the tubing from the cylinder. Concentrations of Vikane™ can be monitored during fumigation using a fumiscope. Because sulfuryl fluoride is odorless and does not irritate the eyes or skin, trace amounts of a warning agent (e.g. chloropicrin, which causes irritation to the eyes, tears, discomfort, and has a noticeable disagreeable pungent odor) are typically introduced into the structure prior to fumigation to act as a warning agent (DowElanco 1994 and 1996a).

Because of a multitude of structural, environmental, and fumigation variations, no two fumigations are alike. The required dosages of Vikane™ are influenced by the temperature at the site of the pest, the length of the exposure period, containment or the rate the fumigant is lost from the structure, and the susceptibility of the pest to be controlled. As a result, dosages vary, however a typical dry wood home fumigation uses 6-16 ounces (0.4 - 1.0 lbs.) per thousand cubic feet. A specially designed Fumiguide™ calculator, which takes into account varying fumigation conditions (e.g., wind speed, relative humidity, tarp condition, volume in cubic feet being treated, soil type around structure, target pest, fan capacity, and exposure duration), is used to determine the required fumigant dosage. Once the fumigation is complete, the fumigator will return to the structure to conduct the aeration procedure (DowElanco 1994 and 1996a).

Aeration, the final step in a fumigation, requires proper ventilation and clearance of Vikane™ and the warning agent from a structure. According to the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL) and the American Conference of Governmental Industrial Hygienists (ACGIH) threshold limit value (TLV) for Vikane™, the fumigator must aerate the structure so that the concentration of sulfuryl fluoride is 5 ppm or less prior to reentry. Reentry must be approved by trained and state-licensed/certified professionals (DowElanco 1996a). Because sulfuryl fluoride has a very high vapor pressure (potential to escape from an area) and a low boiling point (it is a gas at -67 F), it will quickly diffuse from high concentrations within a structure to the outside air where it rapidly dissipates to non-detectible levels (Ultraviolet radiation and reactions with solid particles in the atmosphere catalyze the breakdown of Vikane™) (DowElanco 1994).

The relatively small amounts of sulfuryl fluoride released are calculated to have virtually no impact on the global atmosphere or environment. It is broken down mainly through hydrolysis to release fluoride and sulfide ions. Because it is fully oxidized it does not interact with or contribute to local ozone formation. Furthermore, the relative contribution of sulfuryl fluoride to acid rain is infinitely small compared to massive amounts of sulfur released to the atmosphere from industry. Lastly, sulfuryl fluoride contains no chlorine or bromine and therefore does not contribute to stratospheric ozone depletion (Chambers and Millard 1995, Baily 1992).

Toxicity

Sulfuryl fluoride is a toxic gas that can be handled safely by trained professional fumigators. This gas (as well as methyl bromide) is acutely toxic to humans, although the severity of toxicological effects is dependent on the exposure concentration and exposure duration. Short-term inhalation exposure to high concentrations may cause respiratory irritation followed by pulmonary edema (an accumulation of fluid in the lungs, which can cause death), nausea, abdominal pain, central nervous system depression, and numbness in the extremities. Chronic longer-term inhalation exposure to concentrations significantly above the threshold limit value (TLV) may result in fluorosis (i.e., fluoride binding to the teeth and bones) because sulfuryl fluoride is converted to fluoride ion in the body (DowElanco 1994). Mammalian toxicity by inhalation is about equal to that of methyl bromide (Bond 1984).

Market Trends

Currently, sulfuryl fluoride is used in approximately 85 percent of all structural fumigations, while methyl bromide is used for the remaining 15 percent (Sansone 1996). In California, fumigating dwellings with sulfuryl fluoride has reduced the use of methyl bromide by more than 80 percent. For example, about 2,300 tones of methyl bromide were used in 1990 compared with 430 tones in 1992 (UNEP 1994).

DowElanco supplies 100 percent of the Vikane™ structural fumigation market. The company is currently involved in efforts to increase the use of Vikane™ gas fumigant in two selected markets: 1) quarantine fumigation applications and 2) use in empty food processing facilities. Under current quarantine procedures (USDA-APHIS PPQ Treatment Manual and the AQIS Cargo Container Quarantine Aspects and Procedures Manual), treatment rates for are provided for fumigation of non-food cargo potentially infested with wood-infesting beetles. Efforts are currently underway to develop treatment schedules for additional target insect pests of non-food goods. An additional potential quarantine fumigation opportunity for Vikane™ is the development of treatment schedules to fumigate timber being imported into the United States, Europe, and Japan to control wood-destroying beetles and/or fungal pathogens.

Cost of Fumigating with Vikane™ vs. Methyl Bromide

A general picture of the kinds of fumigation costs associated with using Vikane and Methyl Bromide is provided in the table below. Vikane™ application rates, (and the associated fumigant costs) are derived from the DowElanco Fumiguide calculator system (DowElanco 1996a). This system uses a number of variables that can positively or negatively affect the ability to achieve a lethal concentration. These factors include: the target pest (insect); ground temperature at structure site; structure size; the duration of the fumigation; the foundation type of the structure (slab, crawl space, basement, etc.); and whether or not the fumigation will be monitored. A fumigation performed in warmer months, on larger structures, with a slab foundation or a basement, can be more cost efficient than a comparable fumigation using methyl bromide. As indicated by the figures in the tables below, monitoring sulfuryl fluoride levels to confirm lethal dose during the fumigation utilizes less chemical and is less expensive than fumigation without monitoring.

The following cost breakout examples are for a 35,000 cubic foot structure - a typical home (Table 1), and for a 250,000 cubic foot structure - a commercial structure (Table 2). Cost estimates are for non-monitored and monitored (in parenthesis) fumigations. Label rates for methyl bromide range from 1 to 3 lbs/1000 ft3. The examples listed below use the 1 lb/1000 on a slab foundation and 2 lb/1000 for a structure with a crawl space. The conditions for these examples were: Tarp = good; Seal = Good; Wind = 4mph; Crawl space = sandy loam. The temperature was 75o F and a 24 hour exposure period. The dosages for these examples were calculated on the Fumiguide electronic calculator.

These examples are for fumigations to eliminate drywood termites. Fumigating for other insects (like powder post beetles or wood borers) would increase the amount of fumigant required for Vikane™. There are additional costs that are not considered in these examples. These costs include: 1) Extended aeration times for methyl bromide may require additional manpower and equipment costs for the fumigator. There will also be costs absorbed by the structure owner because the extended aeration period delayed re-occupancy . Methyl Bromide costs for homes would include four nights hotel room rental (1 during fumigation + 3 for aeration) compared to 2 nights (1 during fumigation + 1 aeration) for Vikane™. 2) There also may be potential replacement costs for material which may react with methyl bromide to cause odor problems in fumigated structures.



Table 1. Vikane vs. Methyl Bromide Costs for a Typical Home (35,000 ft3).
Cost Factors ($/1,000 ft3) Vikane:

Crawl Space (Monitored)

Slab Foundation (Monitored)

 Methyl Bromide:

Crawl Space

Slab Foundation

Price per Pound $9.00

$9.00

 $2.75

$2.75

Fumigant Costs $312.30($234.90)

$118.80($89.10)

 $192.50

$96.25

Clearing Equipment $2.40($3.30)

$2.40($3.30)

 $42.50

$42.50

Total Expenses $314.70($238.20)

$121.20($92.40)

$235.00

$138.75

Source: DowElanco 1996b



Table 2. Vikane vs. Methyl Bromide Costs for a Commercial Structure (250,000 ft3).
Cost Factors ($/1,000 ft3) Vikane:

Crawl Space (Monitored)

Slab Foundation (Monitored)

 Methyl Bromide:

Crawl Space

Slab Foundation

Price per Pound $9.00

$9.00

 $2.75

$2.75

Fumigant Costs $1,371.60($1,028.70)

$747.80($561.60)

 $1,375.00

$687.50

Clearing Equipment $2.40($3.30)

$2.40($3.30)

 $85.00

$85.00

Total Expenses $1,374.00($1,032.00)

$751.20($564.90)

 $1,460.00

$772.50



References

Bailey 1992. Sulfuryl Fluoride: Fate in the Atmosphere. Dow Chemical Company. DECO-ES Report 2511. Midland, Michigan.

Bond 1984. Manual of Fumigation for Insect Control. E. J. Bond. FAO Plant Production and Protection. Paper 54.

Bess and Ota 1960. Fumigation of Buildings to Control the Dry-Wood Termite, Cryptotermes brevis. H.A. Bess and A.K. Ota. Journal of Economic Entomology. Volume 53, Number 4, pp. 503-510.

Chambers and Millard. 1995. Assessing the Global Use Potential of Sulfuryl Fluoride. 1995 Annual International Research Conference on Methyl Bromide Alternatives and Emissions Reductions. November 6-8. San Diego, California.

Derrick et al. 1990. Sulfuryl Fluoride (Vikane): A Review of Its Use As a Fumigant. M.R. Derrick. H.D. Burgess, M.T. Baker, and N.E. Binne. Journal of the American Institute for Conservation. Volume 29, Number 1 (Spring 1990), pp. 77-90.

DowElanco. 1994 (November). General Information on Vikane Gas Fumigant. Form No. 311-56-077

DowElanco. 1996a. Vikane™ Gas Fumigant Structural Fumigation Manual.

DowElanco. 1996b. Vikane™ cost comparison to methyl bromide data.

Grey 1960. Vikane™ — A New Fumigant for Control of Drywood Termites. Henry E. Gray. Pest Control Magazine. Volume 48, Number 10, pp. 43-46.

GLCC 1987. Directions for US of Meth-O-Gas 100 ® and Meth-O-Gas ® . Great Lakes Chemical Company. West Lafayette, Indiana.

Kenega 1957. Some Biological Chemical and Physical Properties of Sulfuryl Fluoride as an Insecticidal Fumigant. E.E. Kenega. Journal of Economic Entomology. Volume 50, pp. 1-6.

Meikle and Stewart 1962. Structural Fumigants, the Residue Potential of Sulfuryl Fluoride, Methyl Bromide, and Methane-Sulfonyl Fluoride in Structural Fumigations. Journal of Agriculture and Food Chemistry. Volume 12, p 464-467.

Meikle et al. 1963. Drywood Termite Metabolism of Vikane Gas Fumigant As Shown by Labeled Pool Technique. Journal of Agriculture and Food Chemistry. Volume 11, pp. 226-230.

Osbrink et al. 1987. Laboratory Comparisons of Sulfuryl Fluoride Toxicity and Mean Time of Mortality Among Ten Termite Species (Isoptera: Hodotermitidae, Kalotermitidae, Rhinotermitidae). Journal of Economic Entomology. Volume 80, pp. 1044-1047.

Outram 1970. Some Effects of the Fumigant Sulfuryl Fluoride on the Gross Metabolism of Insect Eggs. Fluoride. Volume 3, pp. 85-91.

Richardson and Roth 1965. Methyl Bromide, Sulfuryl Fluoride and Other Fumigants Against Cochlicella and Pheba Snails. H.H. Richardson and H. Roth. Journal of Economic Entomology. Volume 58, pp. 690-693.

Roth 1973. Fumigants for Quarantine Control of the Adult Brown Dog Tick: Laboratory Studies. Journal of Economic Entomology. Volume 66, Number 6, pp. 1283-1285.

Sansone 1996 (August). Personal Communication. John Sansone. SCC Products, Inc. Anaheim, California.

Stewart 1966. Balanced Fumigation for Better Termite Control. Doane Stewart. Down to Earth. Volume 22, Number 2, pp. 8-10.

Stewart 1957. Sulfuryl Fluoride — A New Fumigant for Control of the Drywood Termite Kalotermes Minor Hagen. Doane Stewart. Journal of Economic Entomology. Volume 50, Number 1, pp. 7-11.

Trinkley 1996 (August). Personal Communication. Mike Trinkley. Chicora Foundation, Inc. Columbia, SC.

UNEP. 1992. Methyl Bromide: Its atmospheric science, technology, and economics. Montreal Protocol Assessment Supplement. United Nations Environment Programme. June.

UNEP. 1994. Montreal Protocol on substances that deplete the ozone layer. United Nations Environment Programme. 1994. Report of the Methyl Bromide Technical Options Committee. 1995 Assessment. EPA 430.

Please note that this publication discusses specific proprietary products and pest control methods. Some of these alternatives are now commercially available, while others are in an advanced stage of development. In all cases, the information presented does not constitute a recommendation or an endorsement of these products or methods by the Environmental Protection Agency (EPA) or other involved parties. Neither should the absence of an item or pest control method necessarily be interpreted as EPA disapproval.

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