Appendix A 

Summary of Efficacy and Other Selected Literature Articles 

A brief summary of various articles describing gas cartridges and their effectiveness (or efficacy) 

follows. Where articles contained information for methods other than the gas cartridges, 

generally only pertinent information about the gas cartridges was included. This literature 

information is not intended to be exhaustive or fully comprehensive. The information is 

provided in chronological order (by date of publication). 

Savarie, P.J., J.R. Tigner, D.J. Elias and Hayes. 1980. "Development of a Simple TwoIngredient Pyrotechnic Fumigant," Proceedings Ninth Vertebrate Conference, U. of 

Nebraska – Lincoln, Year 1980, pp. 215-221. 

Savarie et al. studied a “pyrotechnic fumigant” (a gas cartridge) containing two active 

ingredients (sodium nitrate and charcoal), as opposed to a six active ingredient and two inactive 

ingredient gas cartridge previously produced by the USFWS. The test species were adult 

coyotes (Canis latrans) and wild Norway rats (Rattus norvegicus). They found that the 2-

ingredient gas cartridge was as effective as the six-ingredient one. The cartridge produced 96% 

mortality rate in coyote pups and 77% average (range 35-95%) reduction in number of reopened 

burrows in a rat-infested cattle field lot. 

In simulated coyote dens, tests were performed using individual adult coyotes or coyote pups. 

Comparison of the time to death of the 2-ingredient and the 8-ingredient cartridges yielded 

similar results. Analysis of coyote pups in the simulated coyote dens for percent 

carboxyhemoglobin yielded 70-90% in four tests involving 4-5 pups, each, versus <5% in the 

controls. Field tests, conducted in five states and 98 dens, the percent of pups killed averaged 

96%. Also, six adult females were killed. 

In simulated rodent burrows, a smaller gas cartridge was tested. Three Norway rats were 

exposed during each trial, at three positions of the simulated rodent burrow. Animals located 11 

feet and two branches from the cartridge ignition point died sooner than animals at two other 

positions, 26 feet from the ignition point (4-37 minutes versus 170-420 minutes). Field testing, 

was performed in a Norway rat infested cattle feedlot in Colorado, where on the average, 77% 

percent reduction in number of reopened burrows was observed. 

In separate tests, bobcats (Lynx rufus) were fed rats that were killed by carbon monoxide 

generated from gas cartridges. Bobcats showed no symptoms of intoxication after 7 days of 

feeding 2 rats per day. In most instances, the entire rat carcass was consumed. 

In a hazard assessment of the two ingredient cartridge, the authors indicated that both, charcoal 

and sodium nitrate are relatively non-toxic. They cited Magran (no date), with the following 

reaction: 

 4C + 2NaNO3 Æ 3CO + Na2CO3 + N2 
All these compounds produced are said to be relatively nontoxic as well, except for CO. Carbon 

monoxide combines preferentially over oxygen with hemoglobin, to form carboxyhemoglobin, 

which cannot carry oxygen, causing hypoxia. 

They conclude that the 2-ingredient cartridge is effective, does not show secondary toxicity and 

is safe to humans and the environment due to the fact that it is used underground and 

contamination is minimal. 

Matschke, G.H., K.A. Fagerstone and D.J. Elias. 1980. Evaluation of a fumigant cartridge 

for control of a Richardson’s ground squirrel (Spermophilus richardsonii) population. Job 

completion report for EPA Experimental Use Permit No. 6704-EUP-23, Park County, MO, 

11 pp. 

Matschke, et al. reported to the EPA results of a study related to an Experimental Use Permit, 

using Richardson’s ground squirrels (Spermophilus richardsonii), which are also reported in 

Fagerstone et al. 1981 (see below). It is noted that the authors state factors that may affect 

survival of the test species: weight of the treated animals, length and complexity of the burrows 

(configuration, size and shape), squirrel location within the burrow, cartridge size, and length of 

the cartridge’s fuse since a longer fuse would allow more time to seal the burrow. For more 

details, see below. 

Fagerstone, K., G. Matschke and D. Elias. 1981. Radiotelemetry to evaluate effectiveness of 

a new fumigant cartridge for controlling ground squirrels. In: Long, F.M. (Ed.). 

Proceedings: Third International Conference on Wildlife, July 27-28. Biotelemetry, 3, 20-

25. 

Fagerstone et al. utilized radiotelemetry as a different means of determining the effectiveness of 

sodium nitrate/ charcoal cartridges against burrowing rodents in Montana in 1980. Other 

methods used, such as mark/ recapture, trapping, visual counts or indexes of activity, required 

more time and manpower and/or could not distinguish posttreatment survivors from immigrants. 

Fifty ground squirrels were trapped, weighed, ear tagged, sexed, equipped with radio transmitters 

(164 Hz) and released to the field where they were trapped. The squirrels were located using the 

radio transmitter and burrow entrances surrounding them were treated with gas cartridges. Of 50 

radio equipped squirrels, 43 were located in the field area at the time of treatment, of which 28 

died underground, one died above ground, two were recovered lethargic, but they survived, one 

dug out and escaped, and 11 were retrapped after 2 days. Based on these results, the cartridge 

reduced the population of ground squirrels by ~67%. They recommend increasing the size (total 

weight of the active ingredients) of the cartridge, maintaining the proportion of the sodium 

nitrate to charcoal at 65% to 35%. 

They concluded that radiotelemetry was effective to evaluate the gas cartridge and that it could 

also be used to evaluate other rodent pesticides. They found it to be accurate, independent of 
field conditions (such as weather or immigration of untreated rodents), suitable to obtain time of 

death and location of dead animals, and provided savings in time and manpower. 

Matschke, G.H. and K.A. Fagerstone. 1984. Efficacy of a Two Ingredient Fumigant on 

Richardson’s Ground Squirrels. Vertebrate Pest Conference Proceedings Collection. 

Proceedings of the Eleventh Vertebrate Pest Conference. (D.O. Clark, Ed.) Printed at 

Univ. of California, Davis, CA. pp. 17-19. 

In this study, performed in 1981, ground squirrels (Spermophilus richardsonii) were trapped and 

equipped with radio transmitters in the field in Montana. Then their main burrow was treated 

with sodium nitrate and charcoal cartridges that contained 97 g of combination ingredients, as 

opposed to a previously tested 65 g cartridge (see Fagerstone et al). The ground squirrels were 

monitored and those dead were located via excavation. Of 50 ground squirrels, 41 (82%) died 

and 8 (16%) survived. For 1 (2%) of the squirrels, the radio transmitter failed. 

The authors discussed possible factors that could affect the survival. Diffusion of the toxic gases 

may increase in dryer soils or porous soils, decreasing the effectiveness of the cartridges. Also, 

heavier ground squirrels would be expected to show better survival. 

Zhi, D. and Z.W. Chang. 1986. Efficacy of a Carbon Monoxide Gas Cartridge Against 

Field Rodents. Vertebrate Pest Conference Proceedings Collection. Proceedings of the 

Twelfth Vertebrate Pest Conference, University of Nebraska, Lincoln. (T.P. Salmon Ed.) 

Printed at Univ. of California, Davis, CA. pp. 163-165. 

Zhi and Chang studied and discussed a gas cartridge containing potassium nitrate and sawdust in 

simulated trials, where 100% of 16 albino rats died within 3 minutes. Analysis of cartridge gases 

revealed that carbon monoxide (average 26.46% under the testing conditions) and carbon dioxide 

(average 26.26% under the testing conditions) were main products of the combustion. 

Furthermore, three field trials were performed in China (wheat, maize, rice), where, upon 

excavation, several burrowing animals of numerous species (a total of 9 species) were found 

dead. 

Ramey, C.A., E.F. Schaffer, Jr., K.A. Fagerstone, and S.D. Palmateer. 1992. Back to the 

Future for APHIS’s Vertebrate Pesticides. Proc. 15th Vertebrate Pest Conf. (J.E. Borrecco 

& R.E. Marsh Eds.). Published at University of Calif., Davis. 1992. pp 17-21. 

Ramey et al. surveyed available registrations of vertebrate pesticides. A total of 21 registrations 

were maintained by the Animal and Plant Health Inspection Service (APHIS) for the Animal 

Damage Control (ADC). Two gas cartridges were mentioned, used to control burrowing rodents 

and coyotes, containing sodium nitrate and carbon, and were described briefly. 
Ramey, C.A., E.W. Schaffer, Jr., K.A. Fagerstone, and S.D. Palmateer. 1994. Active 

Ingredients in APHIS’s Vertebrate Pesticides – Use and Reregistration Status. Proc. 16th

Vertebr. Pest Conf. (W.S. Halverson & A.C. Crabb, Eds.). Published at Univ. of Calif., 

Davis. 1994. pp. 124-132. 

In a follow up article, the same authors provided information on the status of reregistration of the 

APHIS vertebrate pesticides, their efficacy and cost, and a view of the future. After providing an 

overview of the history of these pesticides registration and reregistration, they discussed their 

present (as of 1994) status. 

With respect to the gas cartridges, they indicated that the gases generated upon their ignition 

disperse into the atmosphere, are trapped in the soil where they are metabolized by soil 

microorganisms, or enter their elemental cycles (citing a 1994 USDA publication). The CO 

generated is recommended by the American Veterinary Medicine Association because it causes 

rapid death with minimal discomfort. Furthermore, the cartridges do not cause secondary 

toxicity (see Savarie et al 1980) and their labels were modified to treat only burrows with signs 

of active use and to decrease concerns about nontarget hazards. It was indicated that the Large 

Cartridge was approved as of 1993 for use against coyotes (Canis latrans), stripped skunks 

(Mephitis mephitis) and red foxes (Vulpes vulpes) in dens. 

According to the article, APHIS had been completing a number of studies required by the EPA 

and supplemented the database with published articles from the literature. After discussing 

various active ingredients, the authors state that all APHIS vertebrate active ingredients (that is, 

including sodium nitrate and charcoal), are low volume/ minor uses. By developing 

communication and negotiating with the EPA, by proposing less costly alternatives, requesting 

waivers and familiarizing the EPA staff with these pesticides, the cost of the required studies has 

been decreased by around 50%. 

Marsh, R.E. 1994. Current (1994) Ground Squirrel Control Practices in California. Proc. 

16th Vertebr. Pest Conf. (W.S. Halverson & A.C. Crabb, Eds.). Published at Univ. of Calif., 

Davis. 1994. pp. 61-65. 

In his article, Marsh describes current (as of 1994) methods to control the California ground 

squirrel (Spermophilus beecheyi), such as poison baits, burrow fumigation and trapping). The 

squirrel forage competes with livestock and feeds parts of vegetation, including fruits and seeds. 

The author describes its annual life cycle and indicates that knowledge of this cycle is important 

since it is linked to the effectiveness of fumigants. Around three days after fumigation, burrows 

should be retreated if survivors have dug out holes. He says that this control method is more 

efficient if used early after emergence from hibernation, before the females have their young, and 

the soil moisture is high. He suggests to fill in burrow openings with sod and soil. After around 

three days, the entrances of active burrows will be reopened. These are the burrow openings to 

be treated, reducing the waste of fumigants. 
Page, R.J.C. 1994. Laboratory and Field Assessment of a Carbon Monoxide Producing 

Fumigant Cartridge for Use in the Control of Rabbits (Oryctolagus cuniculus). Proc. 16th

Vertebr. Pest Conf. (W.S. Halverson & A.C. Crabb, Eds.). Published at Univ. of Calif., 

Davis. 1994. pp. 175-179.

Page worked with the development of a three-ingredient cartridge capable of producing more CO 

than the sodium nitrate/ charcoal cartridge, to be used against rabbits (Oryctolagus cuniculus) in 

the UK. Even though the cartridge used in simulated warrens was the 3-ingredient one, some of 

the observations are applicable to the 2-ingredient CO cartridge. In preliminary tests, they 

observed that a mixture of 65% sodium nitrate and 35% charcoal produced the highest 

concentration of CO (this is the ratio in the actual cartridges in use in the US, but the experiment 

was developed using raw materials obtained in the UK laboratory). The mixture used by Page 

produced a smaller amount of CO than expected from the amounts of a.i. in the cartridges (9% of 

theoretical). This could be explained in part by the possible formation of carbon dioxide, loss of 

charcoal on ignition, and the fact that some of the charcoal is in powder form and may be 

expelled from the cartridge. 

Page initially found (from previous research), that CO can be produced using magnesite and zinc 

dust following the reaction: 

 MgCO3 + Zn Æ MgO + ZnO + CO 

MgCO3, zinc dust and zinc oxide (ZnO) were added to a sodium nitrate/ charcoal mixture in 

efforts to improve the production of CO. The researcher observed that a mixture of sodium 

nitrate/ charcoal, containing 20% of zinc oxide produced 1.9% CO compared to the mixture 

without zinc oxide, that produced 1.1% CO in a test chamber. The addition of the ZnO is 

believed to undergo the following reactions (however, the exact nature of the reactions is said to 

be unknown): 

 ZnO + C Æ CO + Zn 

 Zn + CO2 Æ CO + ZnO 

Results of tests to verify the effect of gradient on CO gas movement indicated that the mean CO 

concentration was 2.2% near the cartridge (in the entrance of a pipe), 1.0% at the end of the pipe 

in the downward gradient (22o slope) and 0.2% at the end of the pipe in the upward gradient (22o 

slope) (significantly different from site near the entrance of the pipe). 

Studies performed with an artificial rabbit warren showed that the wind speed and direction 

could have an effect on the concentrations of CO and its distribution of CO within the warren. It 

appeared from the results that the diffusion of CO through the tunnels was “very poor.” The air 

temperature increase, expected from the ignition of the cartridges, was confined to the entrances 

of the warren, where temperature of 38oC were registered for one minute. In the tunnels, the 

temperature did not exceed 6oC over temperature prior to ignition of the cartridge. Apparently, 

relatively large amounts of CO were lost by diffusion through the soil, which was apparently 

greater than diffusion along the airspace in the tunnel. Since CO is insoluble in water, 

dissolution in water present in the soil does not explain this issue. 
Ramey, C.A. 1995. Evaluating the Gas Cartridge for Coyotes in Controlling Badgers. 

Sixth Eastern Wildlife Damage Control Conference (1993). Proc. East Wildl. Damage 

Control Conf. 6:79-84, 1995. 

Ramey evaluated the gas cartridge for coyotes (Pocatello Supply Depot) to control badgers 

(Taxidea taxus) in burrows in Texas, used for alfalfa production or for rangeland for livestock in 

1992. The test organisms were equipped with radio transmitters and released to the field. Using 

one gas cartridge, the mortality was 25% (1/4 attempts) while using two cartridges it was 50% 

(1/2 attempts). One badger survived after three attempts of exposure to CO, two of which were 

performed with one cartridge and the third of which was with two cartridges. Possible reasons 

for badgers’ survival could include a tolerance to low levels of oxygen, plugging at the time of 

treatment (they appeared to be sensitive to den disturbance as shown through telemetry), soil 

porosity and moisture, and body weight. It was speculated that the badgers started to plug the 

burrow and dug away while back-filling the burrow behind them. 

Matschke, G.H., C.A. Ramey, G.R. McCann & R.M. Engeman. 1995. Evaluation of a 2-

Active Ingredient Gas Cartridge for Controlling Northern Pockets Gophers. International 

Biodeterioration & Biodegradation (1995)151-160. 

The cartridge studied by Matschke et al. contains a sodium nitrate/ charcoal mixture (at 53%/ 

28%), and two inactive ingredients: Fuller’s earth and borax (at 10% and 9%, respectively), in 

Colorado (oat/ alfalfa/ hay field). The inert ingredients allowed for an extension of the time 

before the combustion of the cartridge materials ignite the walls of the cartridge itself for more 

safety. 

Pocket gophers were monitored using the open-hole index method, using the propensity of the 

pocket gopher to close open burrows. The burrows were considered active if the hole was closed 

and inactive if the burrow was open. Four test areas were established (one of which was a 

control). There was a minimum of 295 ft between test areas and their buffer zones. The areas 

open-hole index was established pre- and post-treatment. 

The percent change in sample plot activity pre and post-testing was +6.7% for the control and 

ranged from -7.1 to -30.8% for the treated areas; although there were differences, they were not 

statistically different. 

Factors affecting Northern pocket gophers’ survival could include: length, volume and shape of 

the burrows; the system is closed, the dead air may delay diffusion of CO; the CO may be lost 

through absorption by the moist and porous soil lining the tunnel. Theoretically, the amount of 

CO generated should be sufficient to kill the northern pocket gophers. The authors believe that 

other factors other than this quantity should be present. 

Ramey, C.A. and E.W. Schaffer, Jr. 1996. The Evolution of APHIS Two Gas Cartridges. 

Proc. 17th Vertebr. Pest Conf. (R.M. Timm & A.C. Crabb, Eds.). Published at Univ. of 

Calif., Davis. 1996. pp. 219-224. 
Ramey and Schaffer, Jr. presented a summary of available information on the Gas Cartridge 

(56228-2) with efficacy demonstrated against Norway rats, Richardson’s ground squirrel, albino 

rats and woodchucks, but not for Northern pocket gophers; and Large Gas Cartridge (EPA Reg. 

No. 56228-21), with efficacy demonstrated against coyotes, striped skunk and red fox, but not 

against badger. They indicated that all data requirements for the cartridges were completed and 

that the concerns for nontarget organisms have been addressed, partly by incorporating 

descriptions of signs of active use by the target species and exclude use during the burrowing 

owls nesting period. 

Hygnstron, S.E. and K.C. VerCauteren. 2000. Cost effectiveness of five burrow fumigants 

for managing black tailed prairie dogs. International Biodeterioration & Biodegradation 

45(2000) 159-168. 

The burrow fumigants evaluated by Hygnstron and VerCauteren included the gas cartridge (GC) 

and aluminum phosphide (AP), and methyl bromide (MB), chloropicrin (CP) and methyl 

bromide-chloropicrin mixture (MBCP) against black tailed prairie dogs in Nebraska in 1989. At 

the present time, of these methods, only the GC and AP are approved for use against prairie 

dogs. The black tailed prairie dog is critical habitat for the endangered black-footed ferret 

(Mustella nigripes) and they benefit numerous species of wildlife; however, it may become a 

threat to livestock production since they can remove up to 80% of the available forage, and to 

agriculture. Also, they are also host to the bacteria of Yersenia pestis. A total of 52 plots, 

including 25 treatments and 25 controls were established; the treated plots were treated 

according to instructions. The GC used contained six ingredients: sodium nitrate, charcoal, 

mineral oil, sawdust, red phosphorous and sulfur. All five methods were efficacious against 

black tailed prairie dogs; the reduction in burrow activity was ≥95% in all instances with no 

statistical differences in efficacy among treatments. The recolonization rate was not monitored 

in this study. The high efficacy was attributed to the heavy low porosity soils, with high soil 

moisture in the field after the snowmelt. It was indicated that as of 1991, nearly 1 million GCs 

were sold; and the 6-ingredient cartridge has been replaced by a 2-ingredient one. With the aid of 

a computer program described elsewhere, cost-benefit of applications of pesticides was 

determined. Costs of materials and labor were higher for the use of the gas cartridge and 

aluminum phosphide while the cost of the application equipment required for the other fumigants 

was higher. Based on a selection criteria proposed by the authors (included humaneness to the 

target species, safety to humans and the environment, availability and cost, likelihood of 

registration by the EPA or the FDA, and preference for the solid fumigant which is easier to 

handle, transport, apply and store-AP and GC), none of the products met all requirements. MB 

and CP are less expensive, but they are not registered for this use, and there are concerns about 

their availability, environmental safety and humaneness. 

Witmer, G.W. and K.A. Fagerstone. 2003. The use of toxicants in black-tailed prairie dog 

management: An overview. Proceedings of the 10th Wildlife Damage Management 

Conference (K.A. Fagerstone, G.W. Witmer, Eds.). 2003. pp. 359-369. (Also at url: 

http://digitalcommons.unl.edu/icwdm_usdanwrc/293/ ). 
Witmer and Fagerstone presented general information on the black-tailed prairie dog methods of 

control (trapping and relocation v. lethal removal), and an overview of the registered pesticides 

against them (aluminum and magnesium phosphide, gas cartridge, acrolein and zinc phosphide). 

Other toxicants that have been used for prairie dog control or are being researched include 

Compound 1080 (sodium fluoroacetate), strychnine, warfarin, chlorophacinone and 

bromadiolone, cholecalciferol, bromethalin, alpha-olefin sulfonate and mustard seed powder. 

For various pesticides, the applicator is required to survey the areas before application. They 

conclude that registered rodenticides are safe when used according to the labels. Factors that 

limit risk are: registration safeguards, low volume of use, use site limited areas and selectivity.