Appendix A Summary of Efficacy and Other Selected Literature Articles

A brief summary of various articl es describing gas cartridges and th eir effectiveness (or efficacy)

follows. Where articles contained informati on 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 orde r (by date of publication).

Savarie, P.J., J.R. Tigner, D.J. Elias and H ayes. 1980. "Development of a Simple TwoIngredient Pyrotechnic Fumigant," Proceedin gs Ninth Vertebrate Conference, U. of Nebraska – Lincoln, Year 1980, pp. 215-221

.

Savarie et al. studied a “pyr otechnic fumigant” (a gas cartr idge) containing two active ingredients (sodium nitrate and ch arcoal), as opposed to a six ac tive ingredient and two inactive ingredient gas cartridge previ ously 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 us ing individual adult coyotes or coyote pups. Comparison of the time to death of the 2-ingred ient 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 cart ridge was tested. Three Norway rats were exposed during each trial, at thr ee positions of the simulated rodent burrow. Animals located 11 feet and two branches from the cartridge igniti on 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 intoxica tion after 7 days of feeding 2 rats per day. In most instan ces, the entire rat carcass was consumed.

In a hazard assessment of the tw o ingredient cartridge, the authors indicated that both, charcoal and sodium nitrate are relatively non-toxic. Th ey cited Magran (no date ), with the following

reaction:

4C + 2NaNO 3 Æ 3CO + Na 2 CO 3 + N 2All these compounds produced are sa id to be relatively nontoxic as well, except for CO. Carbon monoxide combines preferentially over oxyge n with hemoglobin, to form carboxyhemoglobin, which cannot carry oxygen, causing hypoxia.

They conclude that the 2-ingredie nt 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. Elia s. 1980. Evaluation of a fumigant cartridge

for control of a Richar dson’s ground squirrel ( Spermophilus richardsonii ) population. Job completion report for EPA Ex perimental Use Permit N o. 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), squi rrel location within the burrow, cartridge size , and length of the cartridge’s fuse since a longer fuse would a llow more time to seal the burrow. For more details, see below.

Fagerstone, K., G. Matschke and D. Elias. 1981. Radiotelemetry to eval uate effectiveness of a new fumigant cartridge for controlling gr ound 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 di fferent means of determining the effectiveness of

sodium nitrate/ charcoal car tridges against burrowing rodent s in Montana in 1980. Other methods used, such as mark/ recapture, trapping, visual counts or indexe s of activity, required more time and manpower and/or co uld not distinguish posttreatment survivors from immigrants.

Fifty ground squirrels were tra pped, weighed, ear tagged, sexed, equipped with radio transmitters (164 Hz) and released to the fiel d where they were trapped. The squirrels were located using the

radio transmitter and burrow entr ances surrounding them were treate d with gas cartridges. Of 50 radio equipped squirrels, 43 were located in th e field area at the time of treatment, of which 28 died underground, one died above ground, two were r ecovered 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 incr easing the size (total weight of the active ingredient s) of the cartridge, maintainin g 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 pesticid es. They found it to be accurate, independent offield conditions (such as weather or immigration of untr eated rodents), suitab le to obtain time of death and location of dead animals, a nd 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 comb ination 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 ex cavation. 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 factor s that could affect the survival . Diffusion of the toxic gases may increase in dryer soils or po rous soils, decreasing the effectiv eness of the cartridges. Also, heavier ground squirrels would be e xpected to show better survival.

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

Field Rodents. Vertebrate Pest Conference Pr oceedings Collection. Proceedings of the Twelfth Vertebrate Pest Conference, University of Nebraska, Lincoln. (T.P. Salmon Ed.)

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

Zhi and Chang studied and discussed a gas cartri dge 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% unde r the testing conditions) and carbon dioxide (average 26.26% under the testing conditions) were main products of the combustion. Furthermore, three field trials were performe d 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. Fagersto ne, and S.D. Palmateer. 1992. Back to the

Future for APHIS’s Vertebrate Pesticides. Proc. 15 th 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 ve rtebrate pesticides. A total of 21 registrations were maintained by the Animal and Plant Heal th Inspection Service (A PHIS) 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. Fagers tone, and S.D. Palmateer. 1994. Active Ingredients in APHIS’s Vertebrate Pesticides – Use and Reregistration Status. Proc. 16 th

Vertebr. Pest Conf. (W.S. Halv erson & 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 regi stration and reregistrati on, they discussed their present (as of 1994) status.

With respect to the gas cartridges, they indi cated that the gases ge nerated upon their ignition disperse into the atmosphere, are trapped in the soil where they are metabolized by soil microorganisms, or enter their elemental cycl es (citing a 1994 USDA publication). The CO generated is recommended by the American Veteri nary Medicine Association because it causes rapid death with minimal discomfort. Furthe rmore, 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 nontarg et 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 comp leting a number of studies required by the EPA and supplemented the database with published ar ticles from the literature. After discussing various active ingredients, the authors state that all APHIS vertebrate active ingredients (that is, including sodium nitrate and charcoal), ar e 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.

16 th 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 cont rol the California ground squirrel ( Spermophilus beecheyi ), such as poison baits, burrow fumigation and trapping). The squirrel forage competes with liv estock and feeds parts of vegeta tion, including fruits and seeds.

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

since it is linked to the effectiv eness 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 hi bernation, 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 A ssessment of a Carbon Monoxide Producing Fumigant Cartridge for Use in the Control of Rabbits ( Oryctolagus cuniculus ). Proc. 16 th

Vertebr. Pest Conf. (W.S. Halv erson & A.C. Crabb, Eds.). Published at Univ. of Calif., Davis. 1994. pp. 175-179.

Page worked with the development of a three-in gredient cartridge capabl e of producing more CO

than the sodium nitrate/ charcoal car tridge, to be used against rabbits ( Oryctolagus cuniculus ) in the UK. Even though the cartridge used in simula ted 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 nitr ate and 35% charcoal produced the highest concentration of CO (this is the ratio in the actu al 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 e xplained in part by the possible fo rmation 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), th at CO can be produced using magnesite and zinc dust following the reaction: MgCO 3 + Zn Æ MgO + ZnO + CO

MgCO 3 , 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 oxi de produced 1.9% CO comp ared 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 + CO 2 Æ CO + ZnO

Results of tests to verify the e ffect of gradient on CO gas moveme nt indicated that the mean CO

concentration was 2.2% near the car tridge (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 pi pe in the upward gradient (22o slope) (significantly different from site near the entrance of the pipe).

Studies performed with an arti ficial 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 wa s “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 regi stered for one minute. In the tunnels, the temperature did not exceed 6oC ove r temperature prior to ignition of the cartridge. Apparently, relatively large amounts of CO were lost by di ffusion 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 Cartri dge 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 surv ived 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 sp eculated that the badgers started to plug the burrow and dug away while back-f illing 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 Control ling 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 ingredient s: Fuller’s earth and borax (at 10% and 9%, respectively), in Colorado (oat/ alfalfa/ hay field). The inert in gredients allowed for an extension of the time before the combustion of the cartridge materials i gnite the walls of the ca rtridge 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 betwee n test areas and their bu ffer zones. The areas open-hole index was establishe d pre- and post-treatment.

The percent change in sample plot activity pr e and post-testing was + 6.7% for the control and ranged from -7.1 to -30.8% for the treated areas ; although there were diffe rences, they were not statistically different.

Factors affecting Northern pocket gophers’ surviv al 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 lin ing the tunnel. Theore tically, the amount of CO generated should be sufficient to kill the nor thern 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. 17 th 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 No rway rats, Richardson’s ground squirrel, albino rats and woodchucks, but not for Northern poc ket 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 ha ve been addressed, partly by incorporating descriptions of signs of activ e 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. In ternational 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 brom ide (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 th e 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 re move up to 80% of the available forage, and to agriculture. Also, they are al so 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 containe d six ingredients: sodi um nitrate, charcoal, mineral oil, sawdust, red phosphorous and sulfur . All five methods were efficacious against black tailed prairie dogs; the re duction in burrow activity was ≥ 95% in all instances with no

statistical differences in effi cacy among treatments. The recol onization 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 wa s 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 appli cation equipment required for the other fumigants was higher. Based on a selecti on criteria proposed by the authors (included humaneness to the target species, safety to humans and the e nvironment, availability and cost, likelihood of registration by the EPA or the FDA, and preferen ce 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 us e, and there are concerns about their availability, environmen tal 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 10 th 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 inform ation 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, ga s cartridge, acrolein and zinc phosphide). Other toxicants that have been used for prairi e dog control or are be ing researched include Compound 1080 (sodium fluoroacetate), strych nine, warfarin, chlorophacinone and bromadiolone, cholecalciferol, bromethalin, alpha -olefin sulfonate and mustard seed powder. For various pesticides, the appli cator 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 safe guards, low volume of use, use s ite limited areas and selectivity.