Registration Review 

Ecological Risk Assessment and Effects 

Determinations 

Carbon, Carbon Dioxide, Sawdust, Sodium 

Nitrate, Potassium Nitrate and Sulfur 

Gas Cartridges 

Environmental Fate and Effects Division 

Office of Pesticide Programs 

Washington, D.C. 20460 

March 30, 2010

Primary Authors: ERB V Secondary Review:

Valerie Woodard, Ph.D., 

Biologist 

Environmental Fate 

and Effects Div. 

Edward Odenkirchen, Senior 

Scientist 

José L. Meléndez, Chemist Mah T. Shamim, Ph.D., Chief 
Table of Contents 

1 Executive Summary...............................................................................................3 

2. Problem Formulation ..........................................................................................13

2.1 Purpose..........................................................................................................................14 

2.2 Scope..............................................................................................................................15 

2.3 Previous Assessments...................................................................................................16 

2.4 Stressor Source and Distribution ...............................................................................17 

2.5 Action Area...................................................................................................................22 

2.6 Ecosystems Potentially at Risk ...................................................................................23 

2.7 Receptors ......................................................................................................................23 

2.8 Assessment Endpoints and Measures of Ecological Effect ......................................23 

2.9 Conceptual Model........................................................................................................26 

2.10 Analysis Plan ................................................................................................................29 

3. Exposure Assessment...........................................................................................30 

3.1 Label Application Rates and Intervals ......................................................................30 

3.2 Terrestrial Animal Exposure Assessment .................................................................30 

3.3 Terrestrial Plant Exposure Assessment.....................................................................31 

4. Effects Assessment...............................................................................................31 

5. Risk Characterization..........................................................................................32 

5.1 Risk Estimation............................................................................................................32 

5.2 Risk Description...........................................................................................................32 

5.3 Action Area Spatial Analysis......................................................................................39 

6. Uncertainties.........................................................................................................40 

6.1 Exposure Assessment Uncertainties...........................................................................40 

6.2 Effects Assessment Uncertainties ...............................................................................42 

7. Summary and Conclusions..................................................................................42 

8. References.............................................................................................................51 

2
Appendices 

Appendix A Summary of Efficacy and Other Selected Open Literature Articles 

Appendix B Direct Effects to Identified Listed Species 

Appendix C Indirect Effects to Identified Listed Species 

Appendix D Habitat Modification to Identified Listed Species 

Appendix E HED Memo 

Appendix F Potassium Nitrate Mixture Memo 

Appendix G Sodium Nitrate Mixture Memo 

Appendix H Selected Label Restrictions and Instructions for the Gas Cartridges 

Appendix I Nitrate Verification Memo 

Appendix J Papers Accepted for ECOTOX for Carbon 

Appendix K Papers Excluded for ECOTOX for Carbon 

Appendix L Papers on Non-target Efficacy from ECOTOX for Carbon 

Appendix M Papers Rejected for ECOTOX for Carbon Dioxide 

Appendix N Papers Accepted for ECOTOX for Inorganic Nitrates 

Appendix O Papers Not Accepted for ECOTOX for Inorganic Nitrates 

Appendix P Other papers from ECOTOX for Inorganic Nitrates 

Appendix Q ECOTOX Rejection Codes 

Appendix R Carbon ECOTOX Spreadsheet 

Appendix S Inorganic Nitrate Spreadsheet 

Appendix T California Alameda Whipsnake Life History 

Appendix U California Alameda Whipsnake Critical Habitat Designation 

Appendix V California Alameda Whipsnake Primary Constituent Elements 

Appendix W San Francisco Garter Snake Life History 

Appendix X San Joaquin Kit Fox Life History 

Appendix Y Spatial Analysis 

Attachments

Attachment I Supplemental Information on Standard Procedures for Threatened and 

Endangered Species Risk Assessments on San Francisco Bay Species 

Attachment II Status and Life History of the San Francisco bay Listed Species 

Attachment III Baseline Status and Cumulative Effects for the San Francisco Bay Species 

Attachment IV 1996 letter concurring with EPA Region IX 

1 Executive Summary 

The purpose of this assessment is to evaluate potential direct and indirect effects arising from 

FIFRA regulatory actions regarding use of carbon dioxide and use of carbon, sawdust, sodium 

nitrate, potassium nitrate and sulfur cartridges on non-target species (including non-listed and 

federally-listed species). The screening level assessment for the registration review was 

completed in accordance with procedures outlined in the Agency’s Overview Document 

(USEPA, 2004) and the U.S. Fish and Wildlife Service (USFWS) and National Marine Fisheries 

Service (NMFS) Endangered Species Consultation Handbook (USFWS/NMFS, 1998). In 

3
addition to the registration review assessment a refined endangered species assessment has been 

completed to determine the effects of the cartridges on three listed species for which sodium 

nitrate and potassium nitrate were alleged to be of concern in a suit brought against the Agency 

(Center for Biological Diversity (CBD) vs. EPA et al. (Case No. 07-2794-JCS): the threatened 

Alameda whipsnake; endangered San Francisco garter snake; and San Joaquin kit fox. The 

following uses are labeled for carbon, sawdust, sodium nitrate, potassium nitrate and sulfur 

rodenticide and predacide cartridges, and are considered as part of the federal action evaluated in 

this assessment: 

 

• Crops 

• Gardens 

• Golf Courses 

• Lawns 

• Noncrop 

• Open Fields 

• Rangelands 

• Reforested areas 

• Parks 

• Meadows 

Carbon dioxide is registered for indoor uses only. 

The carbon, sawdust, sulfur, sodium nitrate and potassium nitrate cartridge products are 

pyrotechnic devices used against rodents and certain other mammals in burrows, including 

moles, pocket gophers, woodchucks, rats and Norway rats, ground squirrels, skunks, yellowbellied marmots, and prairie dogs. There is a larger gas cartridge used in dens against coyotes, 

red foxes and striped skunks. The cartridges are lit and rapidly inserted in the burrow or den 

openings, which are blocked (sealed) with soil or sod to prevent the gases from escaping. If 

smoke is seen escaping from other burrow openings, they should be plugged with soil or other 

materials. Usually more than one cartridge is applied for a burrow system. 

Two kinds of stressors were identified in this assessment, the toxic gases released by the gas 

producing cartridge products, and carbon dioxide. Carbon, sawdust, sodium and potassium 

nitrates and sulfur are used in pyrotechnic fumigant gas producing cartridge products. After the 

cartridges are ignited they produce gases that cause asphyxiation of the pests. The gases, not the 

active ingredients, are the stressors for these products. Not all the gases have been identified; 

however, it appears that multiple combustion products may be formed, including, for example, 

carbon monoxide, carbon dioxide, nitrogen oxide, sulfur dioxide, and nitrogen. The toxic gases 

displace the oxygen in the burrows and dens, creating an un-breathable atmosphere and causing 

suffocation of the target organisms. 

One example of such a stressor is carbon monoxide; it combines preferentially with hemoglobin 

to form carboxyhemoglobin, which cannot carry oxygen, causing hypoxia (Savarie et al., 1980). 

Various efficacy studies (Savarie et al. 1980, Matschke et al. 1980, Fagerstone et al., 1981, 

Matschke & Fagerstone, 1984; Zhi & Chang, 1986; Matschke et al., 1995 and Ramey, 1995), 

most of which were carried out using two-ingredient cartridges, containing sodium nitrate and 

4
charcoal (or carbon), were evaluated and lead to the conclusion that high levels of mortality are 

expected in burrows and dens treated with cartridges (see Appendix A for more information on 

those studies). 

Based on the application method (i.e., cartridges are placed into sealed burrows/dens), the effect 

of the gas producing cartridges is expected to remain within the application site (localized as 

opposed to widespread). No potential transport from spray drift or run-off is expected from the 

use of gas producing cartridges. Furthermore, no chronic exposure is expected from the 

application of the gas cartridges. The gases will eventually diffuse or disperse in the 

environment, be absorbed (entrapped) by the soil where they are metabolized by soil 

microorganisms or enter their elemental cycles (USDA 1994, cited by Ramey et al,. 1994). 

Because of the fact that target or non-target species are not exposed to the active ingredients 

(carbon, sawdust, sodium nitrate, potassium nitrate and sulfur), in burrows or dens, but instead 

are exposed to the active ingredient’s by-products, all environmental fate and effects data 

requirements were waived for these active ingredients. The gas cartridges may be used in crops, 

but they are not considered conventional pesticides. Because they are used inside burrows or 

dens, they are generally not in contact with the crops. 

Carbon dioxide PC code 016601 is a fumigant used as an insecticide. It is used indoors in sites 

such as sealed trucks, trailers, sealed railroad cars, food handling establishments and ships. The 

area to be fumigated is sealed and the atmosphere filled with a minimum of 60% carbon dioxide 

for four to five days. This causes the pests to die from asphyxiation. No exposure to wildlife, 

from the indoor use of carbon dioxide, is expected when used according to the label. 

Furthermore, the carbon dioxide emitted from the use sites is not considered a threat to nontarget wildlife because the chemical is naturally occurring in the environment. Because carbon 

dioxide is used indoors only, and exposure to non-target species is not expected, all the 

environmental fate and ecological effects data requirements for carbon dioxide were also waived. 

The effects determination assessment endpoints for listed species include direct and indirect 

effects based on toxicity information for birds, which are also used as a surrogate for terrestrialphase amphibians and reptiles, as well as mammals and insects. Direct toxic effects on the 

survival, reproduction, and growth as well as indirect effects, such as reduction of the prey base 

or modification of habitat are considered in the assessment. In the terrestrial habitat, indirect 

effects due to depletion of prey are assessed by considering effects to terrestrial insects, birds, 

small terrestrial mammals, reptiles and amphibians. Indirect effects due to modification of the 

terrestrial habitat are characterized by available data for terrestrial monocots and dicots. 

No aquatic or terrestrial exposure is expected due to the indoor use of carbon dioxide. Therefore 

it is determined that carbon dioxide products covered in this assessment will have No Effect on 

listed or non-listed species. 

Furthermore, no aquatic exposure is expected from the outdoor use of carbon, potassium nitrate, 

sodium nitrate and sulfur cartridge. Therefore, these products are determined to have No Effect 

on listed and non-listed aquatic species. 

5
An initial assessment is conducted for Registration Review to determine the potential effect on 

non-listed species from the use of cartridges from outdoor terrestrial exposures. The agency 

determined that there was the potential for adverse direct effects from the application of the 

cartridges from the combustion products to non-listed birds, mammals and terrestrial 

invertebrates inhabiting burrows or dens. There is also the potential for adverse direct effects to 

non-listed reptiles and amphibians inhabiting burrows or dens based on birds being used as 

surrogates for those species. No direct effects from the use of the cartridges are expected for 

terrestrial plants. The determination is based on asphyxiation from the combustion products 

formed after the cartridge is ignited in the burrow or den and the burrow or den is sealed to retain 

the gases at the site. 

A screening level assessment is also conducted under Registration Review to determine potential 

effects to listed species. If there is a determination that there is a potential for direct or indirect 

effects to listed species, a “may affect” determination is made. If use of the pesticides “may 

affect” the assessed species and/or modify designated critical habitat, the best available 

additional information is considered to refine the potential for exposure and effects, and 

distinguish those actions that “may affect, but are not likely to adversely affect” (NLAA) from 

those actions that are “likely to adversely affect” (LAA) endangered species and its critical 

habitat. 

The Agency makes a “May Affect, LAA” determination for listed burrowing species (birds, 

mammals, insects, and reptiles and amphibians using birds as a surrogate) for survival as an 

acute direct effect based on asphyxiation from the combustion products. The effect from the 

application of the cartridges is localized to the application site based on the label instructions to 

seal the burrow or den following the application. Supporting evidence is based on habitat and 

diet life history information (NatureServe, 2009) for taxa representing listed species identified in 

Appendix B. A “no effect” determination is made for those species not identified in the 

Appendix B. 

Additional supporting information is provided from a 1993 Biological Opinion (BO) as well as 

memos from the USFWS indicating jeopardy to terrestrial mammals and reptiles with specific 

reasonable and prudent alternatives (RPAs) for each species addressed in the BO. The BO 

identified RPAs for 17 specific species. This information was included on two labels, the Gas 

Cartridge and the Large Gas Cartridge. Six of those identified listed species were also included 

on three labels (Dexol Gopher Gasser, Revenge Smoke Bomb and SMOKE’em). One label does 

not include specific listed species information (Giant Destroyer). 

The BO also indicated that even with implementation of the alternatives, there was still risk for 

the San Joaquin kit fox, Point Arena mountain beaver, Fresno kangaroo rat, giant kangaroo rat, 

and Tipton kangaroo rat resulting in an unquantifiable level of incidental take. The current labels 

reflect the need to limit use in the habitat of the Black-footed ferret, San Joaquin kit fox, Utah 

prairie dog, blunt-nosed leopard lizard, Eastern indigo snake and desert tortoise. Additionally, a 

letter from the US Fish and Wildlife Service to EPA’s Region 9 office (November 1, 1996) 

indicated that the California Department of Pesticide Regulation’s (Cal DPR) endangered species 

bulletins that address the potential effects of burrow fumigants to those species addressed in the 

1993 BO, including the SFGS and SJKF, were adequate and could be substituted for the RPAs as 

6
described in the BO. Therefore, the species for which labeling was changed relative to the 1993 

BO and those covered by the Cal DPR bulletins which also were addressed in the 1993 BO are 

adequately protected at this time from potential effects of the burrow fumigants being assessed 

here. Nonetheless, during consultation with the US Fish and Wildlife Service on other species 

potentially affected, EPA will confirm that the measures in place remain adequate and that the 

ranges of these species have remained constant since the 1993 BO and the 1996 letter to EPA 

Region 9. 

Potential indirect effects in the form of reduction in prey for listed species also resulted in a 

“May Affect, LAA” determination for birds, mammals, reptiles and amphibians based on 

asphyxiation from the combustion products. The indirect effects from cartridge application are 

not limited to species inhabiting burrows or dens because some prey are included in the diets of 

listed species that do not inhabit burrows or dens. Supporting evidence is based on diet life 

history information (Nature Serve, 2009) for taxa representing listed species consuming prey 

with burrow/den habitats as reported by USFWS which are identified in Appendix C. A “no 

effect” determination is made for those species not identified in the Appendix C. 

Indirect effects also include potential habitat modification. Habitat modification is based on 

reduction in prey as well as changes in habitat used for shelter or reproduction for species with 

designated critical habitat. The national level determination provides screening level results for 

taxa based on potential effects to identified listed species, which includes if a critical habitat has 

been designated for that species by USFWS in Appendix D. There is a “Habitat Modification” 

determination for listed birds, mammals, reptiles and amphibians based on reduction in prey 

based on a conservative estimate of 100% mortality from the combustion products as well as 

reduction in shelter. Shelter can be reduced due to sealing the burrow or den entrances following 

application of the cartridges, especially for species that use other animal burrows or dens rather 

than creating their own burrows or dens. Habitat Modification for terrestrial invertebrates is 

based on limiting access to the burrows or dens after the pesticide is applied through sealing 

entrances. The Habitat Modification for plants is based on potential for reduction in seed 

dispersal. Because mammals may transport seeds in their fur, dispersal may be reduced due to 

the number of mammals available in a geographic area. Supporting evidence is based on habitat 

life history information (Nature Serve, 2009) for taxa representing listed species consuming prey 

with burrow/den habitats as reported by USFWS which are identified in Appendix D. A “no 

effect” determination is made for those species not identified in the Appendix D. 

These determinations are based on lines of evidence using the best available information. The 

screening level determinations are summarized for Registration Review in Tables 1.1 for nonlisted species and in Table 1.2 for the listed species. The determinations for the three species for 

which refinements have been made are presented in Table 1.3, and the effects determination for 

designated critical habitat for one species for which refinements have been made, is provided in 

Table 1.4. 

7
Table 1.1. Potential Direct Effects on Non-Listed Species Inhabiting Burrows and 

Dens for the Use of Carbon, Sawdust, Potassium Nitrate, Sodium Nitrate and Sulfur 

Cartridges 

Species 

Assessment 

Endpoint Description of Results of Risk Estimation 

Burrowing Birds 

Burrowing 

Mammals 

Burrowing 

Reptiles 

Burrowing 

Amphibians 

Burrowing 

Terrestrial 

Invertebrates 

Survival There is a potential for acute direct adverse effects on burrowing 

species based on asphyxiation from the combustion products at 

the site of application. 

8
1.2 Effects on Listed Species for the Use of Carbon, Sawdust, Potassium Nitrate, 

Sodium Nitrate and Sulfur Cartridges 

Species 

Assessment 

Endpoint 

Effects 

Determination Description of Results of Risk Estimation 

Direct Effects 

Terrestrial 

(Juveniles and adults)

Burrowing 

Birds 

Burrowing 

Mammals 

Burrowing 

Reptiles 

Burrowing 

Amphibians 

Burrowing 

Terrestrial 

Invertebrates 

Direct Effects 

Survival of 

individuals 

via direct 

effects on 

terrestrial 

organisms 

May Affect 

LAA 

The determination for acute direct effects is 

based on 100% mortality from asphyxiation 

based on the combustion products following 

application. 

Indirect Effects 

Birds 

Mammals 

Reptiles 

Amphibians 

Survival of 

individuals 

via reduction 

of prey (i.e.,

birds, 

terrestrial 

mammals, 

reptiles, 

terrestrial 

phase 

amphibians 

and terrestrial 

invertebrates) 

May Affect 

LAA 

The determination for acute indirect effects is 

due to an inability to measure the effect for 

reduction in prey based on asphyxiation from 

the combustion products. The reduction in 

prey may affect both burrowing and nonburrowing listed species consuming animals 

with burrow/den habitats. 

 

9
1.2 Effects on Listed Species for the Use of Carbon, Sawdust, Potassium Nitrate, 

Sodium Nitrate and Sulfur Cartridges 

Species 

Assessment Effects 

Endpoint Determination Description of Results of Risk Estimation 

Birds 

Mammals 

Reptiles 

Amphibians 

Terrestrial 

Invertebrates 

There is a “Habitat Modification” based on a 

reduction in prey from asphyxiation for both 

burrowing and non-burrowing species. 

There is a “Habitat Modification” 

determination for burrowing species based on a 

reduction in cover/shelter. Use of the pesticides 

in cartridge products results in reduced access 

to burrows for shelter or reproduction. 

Terrestrial 

Plants 

Survival of 

endangered 

species via 

effects on 

habitat (i.e.,

reduction in 

prey, shelter, 

riparian 

vegetation) 

Habitat Modification 

There is a habitat modification determination 

for terrestrial plants based on the potential for 

reduction in seed dispersal. 

10
Table 1.3 Effects Determination Summary for Effects of Potassium and Sodium 

Nitrate Cartridges for Three Listed Species 

Species Effects 

Determination 

Basis for Determination 1

Potential for Direct Effects

Terrestrial-phase (Juveniles and Adults): 

Habitats for the snake include shrub communities and adjacent 

habitats of grassland, savanna and oak-bay woodland. The most 

common types of retreat site in both the grassland and scrub 

communities are small rodent burrows and rock crevices, with 

brush piles, deep soil crevices and debris piles also used for 

cover/shelter. The determination for acute direct effects is based on 

100% mortality from asphyxiation based on the combustion 

products following application, if applied to a burrow in which the 

snake is residing during application. 

 

Potential for Indirect Effects

 Alameda 

Whipsnake 

(Masticophis 

lateralis 

euryxanthus) 

(AW) 

May Affect, 

Likely to 

Adversely 

Affect (LAA) 

Terrestrial prey items, riparian habitat 

There is an “LAA” determination for acute indirect effects due to 

prey reduction for the AW consuming lizards, snakes and small 

mammals that may inhabit burrows. The prey may be present at the 

site of application, which results in mortality for the prey. 

Potential for Direct Effects 

Terrestrial-phase (Juveniles and Adults): 

The SFGS uses densely vegetated ponds near open hillsides where 

they can sun themselves, feed, and find shelter in rodent burrows. 

Rodents are targets for nitrate cartridges. The determination for 

acute direct effects is based on 100% mortality from asphyxiation 

based on the combustion products following application if applied 

to a burrow in which the snake is residing during application. US 

FWS has indicated measures put in place by Cal DPR are adequate 

protection for this species relative to uses of burrow fumigants. 

Potential for Indirect Effects 

 San Francisco 

Garter Snake 

(Thamnophis 

sirtalis 

tetrataenia) 

(SFGS) 

May Affect, Not 

Likely to 

Adversely 

Affect (NLAA) 

Terrestrial prey items, riparian habitat 

There is an “NLAA” determination for acute indirect effects due 

to prey reduction. The main diet of adult SFGS consists of 

California Red-Legged Frog (CRLF), which are listed as a 

threatened species (USFWS, 1985 and 2007). CRLFs also use 

small mammal burrows and moist leaf litter as habitat, and might 

be present at the time of application. US FWS has indicated 

measures put in place by Cal DPR are adequate protection for this 

species relative to uses of burrow fumigants. 

11
Table 1.3 Effects Determination Summary for Effects of Potassium and Sodium 

Nitrate Cartridges for Three Listed Species 

Species Effects Basis for Determination 1

Determination 

Potential for Direct Effects 

Terrestrial-phase (Juveniles and Adults): 

The fox inhabits a variety of habitats, including grasslands, grazed 

grasslands, shrublands, meadows, and areas of row crops, orchards 

and vineyards (East Contra Costa County HCP/NCCP, 2006). 

Although kit foxes may dig their own dens, they also modify and 

use those constructed by other animals (ground squirrels, badgers, 

and coyotes). Coyotes and ground squirrels are both target pests. 

The determination for potential acute direct effects is based on 

100% mortality from asphyxiation based on the combustion 

products following application at the application site. US FWS has 

indicated measures put in place by Cal DPR are adequate protection 

for this species relative to uses of burrow fumigants. 

Potential for Indirect Effects 

San Joaquin Kit 

Fox (Vulpes 

macrotis mutica) 

(SJKF) 

May Affect, Not 

Likely to 

Adversely Affect 

(NLAA) 

Terrestrial prey items, riparian habitat 

There are potential acute indirect effects due to prey reduction for 

the SJKF consuming small mammals such as kangaroo rats, 

pocket mice, California ground squirrels and insects that may 

inhabit burrows. Some of the small mammals may also be target 

pests, such as ground squirrels. The prey may be present at the site 

of application, which results in mortality of the prey. However, 

USFWS has indicated measures put in place by Cal DPR are 

adequate protection for this species relative to uses of burrow 

fumigants. 

1

 For more detailed information on the distribution, habitat requirements, and life history information of the 

assessed listed species, see Attachment II. 

12
1.4. Effects Determination Summary for the Critical Habitat Impact Analysis

Designated 

Critical Habitat 

for: 

Effects 

Determination 

Basis for Determination 1

 Almeda 

WhipSnake (AW) 

Habitat 

Modification 

Lines-of-evidence indicate potential adverse effects for reduction in prey for 

the AW consuming species inhabiting burrows. 

The PCEs for the AW include mammal burrows as habitat. Because the 

application method involves closing the burrow openings after inserting the 

cartridge, there would be a reduction in available shelter/cover. 1

 For more detailed information on the distribution, habitat requirements, and life history information of the assessed 

listed species, see Attachment II. 

Given the LAA determination for the CAW and potential modification of designated critical 

habitat for the CAW, a description of the baseline status and cumulative effects for the CAW is 

provided in Attachment III. 

EPA previously requested modification of the labels for the Gas Cartridge and the Large Gas 

Cartridge based on conclusions from the Biological Opinion (1993). That BO identified 17 listed 

species with specific mitigation for each such as time of use and geographic boundaries. In 

addition, memos from USFWS indicated risk to identified mammals and reptiles and included 

mitigation specific to the six identified species. Based on those memos, six listed species were 

included on labels for Dexol Gopher Gasser, SMOKE’em, and Revenge Smoke Bomb. Those 

modified labels provide the basis for the current assessment. 

Based on the conclusions of this assessment, including additional listed species identified and the 

need to review geographic boundaries for current and previously identified listed species, 

consultation will be reinitiated with the U. S. Fish and Wildlife Service under Section 7 of the 

Endangered Species Act. A screening list of endangered species with the potential to be 

adversely impacted by potassium nitrate, sodium nitrate, carbon, sawdust and sulfur cartridges is 

provided in Appendices B-D. A ‘no effect” determination has been made for all other listed 

species and their critical habitat, not identified on the Appendices B-D. 

2. Problem Formulation 

The purpose of the problem formulation is to provide the foundation and a strategic framework 

for the ecological risk assessment. It identifies the important components of the problem and 

focuses the assessment on the most relevant life history stages, habitat components, chemical 

properties, exposure routes, and endpoints. As such, it articulates the purpose and objectives of 

the risk assessment, evaluates the nature of the problem, and provides a plan for analyzing the 

data and characterizing the risk (USEPA, 1998). The structure of this risk assessment is based 

on guidance contained in U.S. EPA’s Guidance for Ecological Risk Assessment (USEPA, 1998). 

13
2.1 Purpose 

This document supports EPA’s registration review of the subject pesticides. This assessment 

evaluates the potential direct effects on non-listed species and direct and indirect effects on listed 

species arising from FIFRA regulatory actions regarding the use of carbon, sawdust, potassium 

nitrate, sodium nitrate and sulfur in fumigant gas producing cartridge products. This assessment 

also addresses potential effects of three species alleged to be of concern in a suit brought against EPA 

(Center for Biological Diversity (CBD) vs. EPA et al. (Case No. 07-2794-JCS)): the Alameda 

whipsnake, the San Francisco garter snake and the San Joaquin kit fox. The Alameda whipsnake 

(Masticophis lateralis euryxanthus) was listed as threatened on December 5, 1997 (62 FR 64306) 

by the U.S. Fish and Wildlife Service (USFWS) (USFWS, 1997 and Westphal, 1998). The San 

Francisco Garter Snake (SFGS) (Thamnophis sirtalis tetrataenia) was listed as endangered on 

March 11, 1967 (32 FR 4001; USFWS 1967) by the U.S. Fish and Wildlife Service (USFWS) 

and was grandfathered under the Endangered Species Act (ESA) when it was signed into law in 

1973. The San Joaquin kit fox (Vulpes macrotis mutica) was listed as endangered on March 11, 

1967 (32 FR 4001) by the U.S. Fish and Wildlife Service (USFWS) (USFWS, 1967). These 

assessments do not include the use of carbon dioxide as an indoor fumigant. They do not include 

sulfur uses other than the gas cartridge use. In 1991, the Reregistration Eligibility Document 

(RED) for the Case No. 4052 (List D), which includes both inorganic nitrates and nitrites was 

issued. By the time of the RED issuance (1991), no nitrite products were registered, and no 

evaluation of nitrite products was performed; for the same reason, no evaluation of nitrite 

products is currently needed. 

Analyses of effects to listed species are conducted. In accordance with the Overview Document 

(US EPA, 2004), provisions of the ESA, and the Services’ Endangered Species Consultation 

Handbook, the assessment of effects associated with registrations of carbon, sawdust, potassium 

nitrate, sodium nitrate and sulfur cartridges are based on an action area. It is noted that the action 

area for a national-level FIFRA regulatory decision associated with a use of carbon, sawdust, 

potassium nitrate, sodium nitrate and sulfur may potentially involve numerous areas throughout 

the United States and its Territories. The action area for the three species for which refined 

assessments were conducted is limited to California. 

As part of the “effects determination,” one of the following three conclusions will be reached 

regarding the potential use of carbon, sawdust, potassium nitrate, sodium nitrate and sulfur in 

accordance with current labels: 

• “No effect”; 

• “May affect, but not likely to adversely affect”; or 

• “May affect and likely to adversely affect”. 

Designated critical habitat (if applicable) identifies specific areas that have the physical and 

biological features, (known as primary constituent elements or PCEs) essential to the 

conservation of listed species. 

If the results of initial screening-level assessment methods show no direct or indirect effects (no 

LOC exceedances) upon individual listed species or upon the PCEs of the species’ designated 

critical habitat (if applicable), a “no effect” determination is made for use of carbon, sawdust, 

14
potassium nitrate, sodium nitrate and/or sulfur as it relates to this species and its designated 

critical habitat. A “no effect” determination is made for those species not identified in the 

Appendices B-D. 

If, however, potential direct or indirect effects to individual species are anticipated or effects may 

impact the PCEs of the species designated critical habitat, a preliminary “May Affect” 

determination is made for the FIFRA regulatory action regarding the chemical(s). If a 

determination is made that the use of carbon, sawdust, potassium nitrate, sodium nitrate and 

sulfur within the action area(s) associated with a species “May Affect” this species or its 

designated critical habitat, additional information is considered to refine the potential for 

exposure and for effects to the species and other taxonomic groups upon which they depend 

(e.g., aquatic and terrestrial vertebrates and invertebrates, aquatic plants, riparian vegetation, 

etc.). Based on the refined information, the Agency uses the best available information to 

distinguish those actions that “May Affect, but are Not Likely to Adversely Affect” from those 

actions that “May Affect and are Likely to Adversely Affect” a species or the PCEs of its 

designated critical habitat. This information is summarized as taxa and presented as part of the 

Risk Characterization in Section 5 of this document. A summary of species with LAA 

determinations can be found in Appendices B and C. Species with potential habitat modification 

are summarized in Appendix D. The determinations for the refined assessment for the three 

species are presented in the executive summary and the conclusion, section 7. 

The Agency believes that the analysis of direct and indirect effects to individual species provides 

the basis for an analysis of potential effects on the designated critical habitat. Carbon, sawdust, 

potassium nitrate, sodium nitrate and sulfur cartridges may directly impact living organisms 

within the action area (defined in Section 2.5). Critical habitat analysis for these six chemicals is 

limited in a practical sense to those PCEs of critical habitat that are biological or that can be 

reasonably linked to biologically mediated processes (i.e., the biological resource requirements 

for the listed species associated with the critical habitat or important physical aspects of the 

habitat that may be reasonably influenced through biological processes). Activities that may 

modify critical habitat are those that alter the PCEs and appreciably diminish the value of the 

habitat. Evaluation of actions related to use of carbon, sawdust, potassium nitrate, sodium nitrate 

and sulfur that may alter the PCEs of a species’ critical habitat form the basis of the critical 

habitat impact analysis. 

2.2 Scope 

The end result of the EPA pesticide registration process (i.e., the FIFRA regulatory action) is an 

approved product label. The label is a legal document that stipulates how and where a given 

pesticide may be used. Product labels (also known as end-use labels) describe the formulation 

type (e.g., liquid, granular or cartridge), acceptable methods of application, approved use sites, 

and any restrictions on how applications may be conducted. Thus, the use or potential use of 

carbon, sawdust, potassium nitrate, sodium nitrate, and sulfur cartridges in accordance with the 

approved product labels is “the action” relevant to this ecological risk assessment. 

Carbon (PC Code 016001), including carbon as sawdust, potassium nitrate (PC Code 076103 ), 

sodium nitrate (PC Code 076104) and sulfur (PC Code 077501) used as rodenticide and 

15
predacide fumigants in gas cartridges include multiple active ingredients. This single assessment 

evaluates all these chemicals. The six registered gas cartridge products include various active 

ingredients formulated as mixtures (refer to Table 2.1). SMOKE’em (4-463) includes potassium 

nitrate, sulfur and sawdust as active ingredients. Dexol Gopher Degasser (192-49) and Revenge 

Rodent Smoke Bomb (9086-4), both include potassium nitrate, sulfur and carbon as active 

ingredients. The Giant Destroyer (10551-1) includes sodium nitrate, sulfur and carbon. The 

Large Gas Cartridge (56228-21) and the Gas Cartridge (56228-2), both include sodium nitrate 

and carbon as active ingredients. 

2.3 Previous Assessments 

2.3.1 Previous Assessments

In 1991, the Agency issued Reregistration Eligibility documents for carbon dioxide and carbon, 

sodium nitrate and potassium nitrate, and sulfur cartridges that serve as the basis for this 

assessment. At the time sawdust as an active ingredient was not included in the document. It 

was concluded that, for these active ingredients, application of the cartridges to burrows 

(subsurface) precludes exposure to avian and aquatic organisms. However, organisms that live 

in burrows and dens, including listed species, may be impacted. For carbon dioxide, with only 

indoor uses, the Agency concluded that exposure to non-listed or listed species was unlikely. 

The current labels for the Gas Cartridge and the Large Gas Cartridge reflect proposed mitigation 

measures to reduce potential listed species effects identified in the 1991 Reregistration Eligibility 

Document (RED). 

The problem formulation for Registration Review was submitted March 18, 2008. There have 

been no additional fate or ecological studies reviewed since the problem formulation was 

completed. No major changes have been made to the Problem Formulation; however, the 

conceptual model was modified to include indirect effects to non-target species and additional 

use information was included. The analysis plan submitted in the problem formulation remains 

the basis for this assessment. 

2.3.2 Literature Information and Efficacy Studies

A brief summary of various articles found in the literature is presented in Appendix A. The 

summary of the articles presents information on the effectiveness (or efficacy) of the gas 

cartridges (most of the information referred to cartridges containing carbon and sodium nitrates). 

Where articles contained information for methods other than the cartridges, emphasis was put 

into the cartridges, and information on other methods was included only if it related to the use of 

cartridges. The cartridge literature search provided useful information about their use, methods 

to assess their efficacy, and factors that affect the efficacy of the cartridges. The following are 

example articles that presented information about efficacy: Savarie et al., 1980; Matschke et al.,

1980,; Fagerstone et al., 1981; Matschke & Fagerstone, 1984; Zhi & Chang, 1986; Matschke et 

al., 1995 and Ramey, 1995. Using a variety of methods to quantize the efficacy, it was variable. 

According to various of the articles, the USEPA requirement of efficacy, and the minimum level 

of mortality desired for the cartridge products is 70%; but for certain species, this level of 

16
mortality was not achieved (e.g. for badgers, see Ramey 1995 in Appendix A), and such species 

were not claimed as target species in the labels for the cartridge products. 

2.4 Stressor Source and Distribution 

2.4.1 Nature of the Chemical Stressor

The toxic gases released in the gas producing cartridge products were identified as the stressors 

in this assessment. Carbon, sawdust, sodium and potassium nitrates and sulfur are used in 

pyrotechnic fumigant gas producing cartridge products. After the cartridges are ignited they 

produce gases that cause asphyxiation of the pests. The gases, not the active ingredients are the 

stressors for these products. Not all the gases have been identified; however, it appears that 

multiple combustion products are formed, including as examples, carbon monoxide, carbon 

dioxide, sulfur dioxide and nitrogen gas. The gases displace the oxygen in the burrows, creating 

an un-breathable atmosphere and causing suffocation of the target organisms. An example of a 

possible combustion reaction (Magran, no date, as cited by Savarie et al, 1980) is: 

4C +2NaNO3 → 3CO (g) + Na2CO3 + N2 (g) 

All these compounds are considered relatively non-toxic, except for carbon monoxide. In 

mammals and other organisms, it causes hypoxia (see Section 2.4.3). 

2.4.2 Environmental Transport Mechanisms

Based on the application method, the effect of the gas producing cartridges is expected to remain 

at the application site (localized as opposed to widespread). The primary transport mechanism 

for the cartridges combustion by-products is expected to be diffusion. The soils are expected to 

absorb or entrap part of the gases produced, where they are metabolized by soil microorganisms 

or enter their elemental cycles, while the remainder may be slowly lost to the environment (see 

USDA 1994, as cited by Ramey et al. 1994). Generally, the effect expected from exposure to 

these gases will be acute and it will be mortality. Based on the exposure expected from the gas 

cartridges, no modeling is required (see Section 3.2). The efficacy studies support a conservative 

assumption of 100% mortality from exposure to these gases (see Appendix A for further details). 

No potential transport from spray drift or run-off is expected from the use of gas producing 

cartridges because they are used in sealed burrows. 

2.4.3 Mechanism of Action

Gas cartridges containing carbon, sawdust, potassium nitrate, sodium nitrate and sulfur are 

fumigants for outdoor use. The release of toxic gases (e.g. carbon monoxide and sulfur dioxide) 

after ignition in sealed burrows induces asphyxiation of organisms that live in burrows or dens. 

One example of such toxic gas is carbon monoxide [CO (g)]. It combines with hemoglobin 

(preferentially over oxygen), to form carboxyhemoglobin (preferentially over oxyhemoglobin). 

The hemoglobin is then unable to transport oxygen, causing hypoxia (i.e. the body is deprived of 

an adequate supply of oxygen), and eventually, death. A memo dated March 6, 2008 from the 

17
Human Health Effects Division of EPA supports the mode of action (Appendix E) (see also 

Savarie et al., 1980). 

2.4.4 Use Characterization

Analysis of labeled use information is the critical first step in evaluating the federal action. The 

current labels for carbon, sawdust, potassium nitrate, sodium nitrate and sulfur gas cartridge 

products represent the FIFRA regulatory action. Therefore, labeled use and/or application rates 

specified on the label form the basis of this assessment. The assessment of use information is 

critical to the development of the action area and selection of appropriate modeling scenarios and 

inputs. 

Table 2.1 summarizes information derived from the six labels for the gas cartridge products. The 

table provides product names, percentages of active ingredients, target species and use sites for 

the labels considered in this assessment. It is noted that the gas cartridges may be used in crop 

sites; however, they are not conventional pesticides. Generally they are confined to the treated 

burrows or dens and are not in close contact with the crops. The active ingredients in the gas 

cartridges are not restricted use pesticides. Cartridges may not be used in or around buildings. 

Table 2.1. Cartridge Products Containing Carbon or Sawdust plus Sodium or Potassium 

Nitrate and Sulfur 

Product Name, 

Reg No. Active Ingredients % 

Target Species; 

Use Areas 

SMOKE’em 

4-463 

Potassium nitrate 46.2% 

Sulfur 34.8% 

Sawdust 8.7% 

Woodchucks, ground squirrels; 

Open fields, non-crop areas 

Dexol Gopher 

Degasser 

192-49 

Potassium nitrate 45.0% 

Sulfur 45.0% 

Carbon 8.0% 

Gophers, ground squirrels; 

Lawns, golf courses, gardens, rangeland 

Revenge Rodent 

Smoke Bomb 

9086-4 

Potassium nitrate 38.8% 

Sulfur 39.4% 

Carbon 12.5% 

Gophers, woodchucks, rats, skunks, ground 

squirrels; 

Lawns, golf courses, non-crop areas, rangeland, 

meadows, reforested areas, open fields, parks 

The Giant Destroyer 

10551-1 

Sodium nitrate 46.2% 

Sulfur 34.8% 

Carbon 8.7% 

Gophers, moles, woodchucks, rats, skunks, ground 

squirrels; 

Lawns, golf courses, non-crop areas, rangeland, 

meadows, reforested areas, open fields 

Large Gas Cartridge 

56228-21 

Sodium nitrate 53.0% 

Carbon (Charcoal) 28.0% 

Coyotes, red foxes, striped skunks; 

In dens only in rangeland, crop and non-crop areas 

Gas Cartridge 

56228-2 

Sodium nitrate 53.0% 

Carbon (Charcoal) 28.0% 

Woodchucks, yellow bellied marmots, ground 

squirrels, black tailed prairie dogs, white tailed 

prairie dogs, Gunnison prairie dogs; 

Open fields, non-crop areas, rangeland, reforested 

areas, lawns, golf courses 

Although all six formulated products are mixtures, the Agency does not routinely include, in its 

risk assessments, an evaluation of mixtures of active ingredients. There is no data for individual 

active ingredients and no data for mixtures containing carbon, nitrates or sulfur as active 

18
ingredients. Summaries of data available for the cartridge mixtures are presented in Appendices 

F and G. 

Selected label restrictions are included in Appendix H. There are two common elements across 

the labels. One is that the use of the cartridges is restricted to active sites, where target 

organisms are present. For example, the Environmental Hazards section of the labels for Dexol 

Gopher Gasser, the Gas Cartridge, the Large Gas Cartridge, and Revenge Rodent Smoke Bomb, 

says: “This product is highly toxic to wildlife. Check all burrows for signs of non-target species. 

If present, do not treat burrows.” Therefore, according to the instructions, the sites are required 

to be inspected prior to cartridge use. The other element is that all six labels require the 

entrance(s) to the burrow or den to be sealed at the time of application of the cartridge. 

However, there are also differences across the labels. Five of the six labels are for burrow 

applications. The only common target species identified in all five burrow labels is the ground 

squirrel. The sixth label identifies coyotes, red foxes and striped skunks as target organisms, in 

dens. A verification memo from the Registration Division of EPA (2/19/2010) indicates no 

nitrate products have been cancelled or any rate changes approved as part of the reregistration 

process (Appendix I). 

The Screening Level Usage Analysis (SLUA) was verified for these chemicals. The SLUA 

provides the average annual pounds of pesticide applied for each agricultural crop (i.e. for the 

states surveyed, not for the entire U.S.). According to the SLUA for sodium nitrate, dated 

6/15/07, it appears that crops of major use for the chemical are almonds, kiwifruit, nectarines, 

olives, pistachios, and prunes and plums. In each case, <500 lb of active ingredient were used. 

However, it is indicated that ≥95% of the U.S. acres that have this gas cartridge use are in 

California. For potassium nitrate, the SLUA, also dated 6/15/07, lists almonds, nectarines, 

pistachios and prunes and plums as the crops of interest, but <500 lb active ingredient were 

utilized. As in the previous case for sodium nitrate, it is indicated that ≥95% of the U.S. acres 

that have potassium nitrate gas cartridge use are in California. SLUA data sources include: 

USDA-NASS (United States Department of Agriculture's National Agricultural Statistics 

Service); Private Pesticide Market Research, NPUD 2002 (National Pesticide Use Database) of 

the CropLife America Foundation and California DPR data. Results reflect amalgamated data 

releasable to the public. Given these facts, and provided that all the cartridge products contain 

either sodium nitrate or potassium nitrate, the usage in California becomes particularly relevant. 

Although no typical usage data (number of applications, “rate” or interval between applications) 

is available for carbon or sawdust, the Agency’s Biological and Economic Analysis Division 

(BEAD) provided a use summary, based on the California’s Department of Pesticide Regulation 

Pesticide Use Reporting (CDPR PUR) database. The California Department of Pesticide 

Regulation’s Pesticide Use Reporting database provides a census of pesticide applications in the 

state (Table 2.2-2.3). See http://www.cdpr.ca.gov/docs/pur/purmain.htm . Agricultural uses 

reported in the CDPR PUR database include applications to parks, golf courses, cemeteries, 

rangeland, pastures, and along roadside and railroad rights-of-way. For the gas cartridges, the 

labels restrict the uses in residential sites. 

Publicly available data from the California Department of Pesticide Regulation was used to 

produce the following table (2.2) outlining the pounds of carbon used for cartridges in California 

19
over the three most recent years available at the time the data was gathered (2003-2005). The 

major “crop/ areas” for carbon were vertebrate control, right-of-way and landscape maintenance. 

20
Table 2.2. Carbon Usage 

Crop/Area 2003 Lbs. 

Applied

2004 Lbs 

Applied

2005 Lbs. 

Applied

ALMOND 40 29 17

CHERRY 4 1

GRAPE 30

KIWI 0.1

LANDSCAPE MAINTENANCE 283 145 110

LEMON 1

NURSERY OUTDOOR TRANSPLANTS 2 3

NURSERY GREENHOUSE 

TRANSPLANTS 2

NECTARINE 3

OAT (FORAGE - FODDER) 2

PEAR 0.1 2

PISTACHIO 28 18

RANGELAND 3

REGULATORY PEST CONTROL 9 16 42

RESEARCH COMMODITY 0.01 0.03

RIGHTS OF WAY 376 488 570

STRUCTURAL PEST CONTROL 3 1 2

UNCULTIVATED AG 9

VERTEBRATE CONTROL 1,296 345 224

WALNUT 4 11 37

Chemical Total 2,051 1,047 1,056

Prepared by: Jenna Carter 7/31/07

Publicly available data from the California Department of Pesticide Regulation was used to 

produce Table 2.3, outlining the pounds of sawdust used in California over the three most recent 

years. Only 0.143 to 1.417 lbs of sawdust were used from 2003 to 2005 in California, and they 

were mostly used for landscape maintenance and vertebrate control. 

Table 2.3. Sawdust Usage 

Crop/Site 2003 Lbs. 

Applied

2004 Lbs. 

Applied

2005 Lbs. 

Applied

CHERRY 0.11

LANDSCAPE 

MAINTENANCE 0.4956 0.88 0.011

STRUCTURAL PEST 

CONTROL 0.12

21
VERTEBRATE CONTROL 0.5412 0.5368 0.022

Chemical Total 1.1568 1.4168 0.143

Prepared by: Jenna Carter 8/01/07 

For sulfur containing cartridges, the California Department of Pesticide Regulation (CDPR) use 

information data indicate that the use for “vertebrate control” in the period of 2003 to 2005 

ranged from 453 to 4418 lbs. Sulfur has uses other than cartridges; therefore, the usage table is 

not included. 

It appears that the acreage treated with gas cartridges is usually relatively small, as suggested by 

an informational sheet from the Montana Department of Agriculture. According to the leaflet, 

available on the internet, fumigants, such as cartridge products, “are effective tools for follow up 

of poison bait applications.” It further says that, “Burrow fumigants can also be used as a 

primary control technique although cost of materials and labor generally restrict their use to 

small acreages or sparse populations.” Hygnstrom & VerCauteren (2000) evaluated the 

effectiveness and cost of five burrow fumigants used to manage black-tailed prairie dogs: methyl 

bromide, chloropicrin, methyl bromide-chloropicrin mixture, aluminum phosphide and gas 

cartridges. (Note: At the present time, methyl bromide and chloropicrin are not registered for 

this use.). No difference in efficacy was found among treatment methods (≥95% reduction); but 

costs of aluminum phosphide and gas cartridges were around twice that for the other fumigants. 

2.5 Action Area 

The definition of action area requires a stepwise approach that begins with an understanding of 

the federal action. The federal action is defined by the currently labeled uses for carbon, 

sawdust, potassium nitrate, sodium nitrate and sulfur cartridges. 

For a nationwide risk assessment conducted under Registration Review, the action area will 

encompass the entire United States and its territories. The purpose of defining the action area as 

the entire United States and its territories is to ensure that the initial area of consideration 

encompasses all areas where the pesticide may be used now and in the future. 

It is important to note that the nationwide action area does not imply that direct and/or indirect 

effects and critical habitat modification are expected to or likely to occur over the full extent of 

the action area, but rather to identify all listed species and critical habitat that may be potentially 

affected by the action. The Agency will use more rigorous analysis including consideration of 

available land cover, toxicity data and exposure information to determine areas where individual 

listed species and designated critical habitat may be affected or modified via endpoints 

associated with survival, growth or reproduction. 

22
2.6 Ecosystems Potentially at Risk 

The terrestrial ecosystems potentially at risk for the use of the cartridges are widespread, but are 

geographically limited following application. The gas cartridges may be used in sealed burrows 

in such areas as open fields, non-crop areas, rangeland, reforested areas, lawns and golf courses. 

Also, they may be used in dens, in rangeland, crop and non-crop areas. However, these uses 

result in limited exposure to wildlife off the burrows or dens. Areas adjacent to the treated site 

could include cultivated fields, fencerows and hedgerows, meadows, fallow fields or grasslands, 

woodlands, riparian habitats and other uncultivated areas. Because the cartridges are applied in 

burrows and dens that are sealed, minimal exposure is expected away from the burrows, and in 

areas adjacent to the treated field. Generally the ecosystems at risk consist of the burrow (or 

den) system only. 

The sealed burrow application of carbon, sawdust, sodium nitrate, potassium nitrate, and sulfur 

gas cartridge is not expected to result in exposure to aquatic ecosystems. 

2.7 Receptors 

The receptor is the biological entity that is exposed to the stressor (USEPA, 1998). Various 

types of receptors, including birds, rodents and other small mammals, reptiles, amphibians and 

terrestrial invertebrates, may inhabit burrows and may be exposed to carbon, sawdust, potassium 

nitrate, sodium nitrate and sulfur products applied in the form of gas cartridges. These gas 

cartridges have outdoor uses only. 

As indicated earlier, the pest species are not exposed to the active ingredients in gas cartridges, 

but rather to the products of their combustion. The cartridge application is subsurface into 

burrows, so exposure to aquatic organisms and most birds or mammals (those that do not inhabit 

burrows) is not anticipated. Any organism inhabiting or present in burrows (or dens) at the time 

of pesticide application may be exposed to the stressors, and impacted by the cartridges. 

Therefore, there are potential direct impacts to non-listed species and direct and indirect effects 

to listed species. 

Consistent with the process described in the Overview Document (USEPA, 2004) risk 

assessments use a surrogate species approach in its evaluation of pesticides such as carbon, 

sawdust, potassium nitrate, sodium nitrate and sulfur cartridges. Data from surrogate test species 

are intended to be representative of broad taxonomic groups, and are used to extrapolate 

potential effects on a variety of species (receptors) included under these taxonomic groups. 

Although all toxicity data requirements for the gas cartridge use of carbon, sawdust, potassium 

nitrate, sodium nitrate and sulfur have been waived, additional lines of evidence are available to 

support conclusions. 

2.8 Assessment Endpoints and Measures of Ecological Effect 

Assessment endpoints are defined as “explicit expressions of the actual environmental value that 

is to be protected” (USEPA, 2004). Defining an assessment endpoint involves two steps: 1) 

identifying the valued attributes of the environment that are determined to be at risk; and 2) 

23
operationally defining the assessment endpoint in terms of an ecological entity (i.e., a community 

of burrowing animals) and its attributes (i.e., survival and reproduction). Therefore, selection of 

the assessment endpoints is based on valued entities (i.e., ecological receptors), the ecosystems 

potentially at risk, the migration pathways of pesticides and the routes ecological receptors are 

exposed to pesticide-related contamination. The selection of clearly defined assessment 

endpoints is important because they provide direction and boundaries in the risk assessment for 

addressing risk management issues of concern. Changes to assessment endpoints are typically 

estimated from the available toxicity studies, which are used as the measures of effects to 

characterize potential ecological risks associated with exposure to pesticides such as carbon, 

sawdust, potassium nitrate, sodium nitrate and sulfur. For this assessment, several efficacy and 

other publicly available articles were evaluated. In addition, the mode of action of the cartridge 

products was taken into consideration when determining assessment endpoints. Based on this 

information, the assessment endpoint is survival. Furthermore, a conservative assumption of 

100% mortality is assumed, for organisms inhabiting treated burrows or dens. 

Registrant submitted ecological toxicity data were waived for carbon, sawdust, potassium nitrate, 

sodium nitrate and sulfur based on gas cartridge use patterns due to lack of any direct adverse 

effects on non-target species associated directly to the active ingredients of the cartridge 

products. No additional data are required to determine relevant endpoints. 

2.8.1. Assessment Endpoints 

Assessment endpoints for non-listed and listed species include direct effects on the survival as 

well as indirect effects, such as reduction of the prey base from a reduction in survival from the 

combustion products. In addition, potential modification of critical habitat is assessed by 

evaluating potential effects to PCEs, which are components of the habitat areas that provide 

essential life cycle needs, those components necessary for the survival, growth and reproduction 

of the listed species. Each assessment endpoint requires one or more “measures of ecological 

effect,” defined as changes in the attributes of an assessment endpoint or changes in a surrogate 

entity or attribute in response to exposure to a pesticide. 

The only assessment endpoint for direct effects is survival. Due to a conservative estimate of 

100% mortality from the combustion products expected at the site of application, no toxicity 

studies will be used in this assessment. Endpoints assessed for indirect effects include survival, 

growth and reproduction. 

Assessment Endpoints for Designated Critical Habitat 

As previously discussed, designated critical habitat is assessed to evaluate actions related to the 

use of carbon, sawdust, potassium nitrate, sodium nitrate and sulfur cartridges that may alter 

PCEs of listed species’ critical habitat. Actions that may modify critical habitat are those that 

alter the PCEs and jeopardize the continued existence of the listed species. It should be noted 

that evaluation of PCEs as assessment endpoints is limited to those of a biological nature (i.e., 

the biological resource requirements for the listed species associated with the critical habitat) and 

those for which effects data are available. 

24
Adverse modification to the critical habitat of listed species includes, but is not limited to, the 

following, as specified by USFWS (1998): 

1. Alteration of chemical characteristics necessary for normal growth and 

viability of juvenile and adult endangered species. 

2. Alteration or elimination of the listed species’ food sources or prey base. 

Some components of these PCEs are associated with physical abiotic features (e.g., presence 

and/or depth of a water body, or distance between two sites), which are not expected to be 

measurably altered by use of pesticides. Assessment endpoints used for the analysis of 

designated critical habitat are based on the adverse modification standard established by USFWS 

(2006). 

2.8.2 Incident Reports

An ecological incident is defined as an event(s) in which pesticide use is known or suspected of 

causing the death or other adverse toxicological effects to wild animals and plants other than the 

intended target species. Incidents for animals may include any type of free-ranging wild animal, 

including birds, mammals, fish, reptiles, amphibians and invertebrates, although incidents 

involving invertebrates other than bees and crayfish are rarely reported. Plant incidents may 

include adverse effects to any wild plant, although almost all plant incident reports EFED 

receives are for damage to crops and ornamentals. Incidents of adverse effects to humans, pets 

and domestic animals are not considered ecological incidents. 

There are three primary sources for obtaining information on ecological incidents: 1) the 

Ecological Incident Information System (EIIS, v.2.1), 2) the Avian Incident Monitoring System 

(AIMS) and 3) 6(a)(2) incident reports. The Agency’s Ecological Incident Information System 

(EIIS), maintained by the Agency’s Office of Pesticide Programs, and the Avian Monitoring 

Information System (AIMS), maintained by the American Bird Conservancy, do not contain any 

reports of damage or adverse effects to non-target organisms attributed to the use of carbon, 

sawdust, potassium nitrate, sodium nitrate or sulfur gas cartridges. There are also no reports for 

carbon dioxide indoor fumigant uses. No incidents of contamination of surface, ground and 

drinking water have been reported to the Agency. 

In addition to reviewing major incidents recorded in EIIS and AIMS, minor incidents are 

recorded as aggregated incident reports in the 6(a)(2) Incident database maintained by the 

Agency’s Office of Pesticide Programs. Pesticide registrants report certain types of incidents to 

the Agency as aggregate counts of incidents occurring per product per quarter. Ecological 

incidents reported in aggregate reports include those categorized as ‘minor fish and wildlife’ (WB), ‘minor plant’ (P-B), and ‘other non-target’ (ONT) incidents. ‘Other non-target’ incidents 

include reports of adverse effects to insects and other terrestrial invertebrates. Although there is a 

minor fish incident reported for sulfur, that product is not a cartridge and is not being evaluated 

in the current risk assessment. For carbon, potassium nitrate, sodium nitrate and sulfur cartridges, 

registrants have reported 0 minor fish and wildlife incidents, 0 minor plant incidents, and 0 other 

non-target incidents. 

25
 

2.9 Conceptual Model 

For a pesticide to pose an ecological risk, it must reach ecological receptors in biologically 

significant concentrations. An exposure pathway is the means a pesticide moves in the 

environment from a source to an ecological receptor. For an ecological pathway to be complete, 

it must have a source, a release mechanism, an environmental transport medium, a point of 

exposure for ecological receptors and a feasible route of exposure. 

A conceptual model provides a written description and visual representation of the predicted 

relationships between the stressor (carbon, sawdust, potassium nitrate, sodium nitrate and sulfur 

cartridges by-products), potential routes of exposure and the predicted effects for the assessment 

endpoint. A conceptual model consists of two major components: a risk hypothesis and a 

conceptual diagram (USEPA, 1998). 

2.9.1 Risk Hypotheses

A risk hypothesis describes the predicted relationship among the stressor, exposure and 

assessment endpoint response along with the rationale for their selection. For this assessment, the 

risk is stressor-linked, where the stressor is the release of carbon, sawdust, potassium nitrate, 

sodium nitrate, or sulfur by-products to the environment. These by-products are toxic gases, 

product of the combustion of the cartridges material. The following risk hypotheses are being 

employed for this assessment for the by-products, not the active ingredients: 

• Given the uses of carbon, sawdust, potassium nitrate, sodium nitrate and sulfur cartridges and 

their environmental fate properties, there is a likelihood of exposure to non-target terrestrial 

organisms to the combustion by-products. 

• When used in accordance with the label, carbon, sawdust, potassium nitrate, sodium nitrate 

and sulfur cartridges result in potential adverse effects upon the survival, growth, and 

reproduction of non-target terrestrial organisms. 

2.9.2 Diagram

The conceptual model is a graphic representation of the risk hypothesis, and assumes that as 

rodenticides/ predacides with an inhalation toxic mode of action, carbon, potassium nitrate, 

sodium nitrate, sulfur and sawdust by-products are capable of affecting terrestrial animals 

provided that environmental concentrations are sufficiently elevated as a result of proposed label 

uses. There is less concern for aquatic animals because exposure is expected to be minimal. 

Through a preliminary iterative process of examining available data, the conceptual model has 

been refined to reflect the likely exposure pathways and the organisms that are most relevant and 

applicable to this assessment (Fig.2.1). It specifies the stressors (reaction by-products from the 

gas cartridge use, (e.g. carbon monoxide, carbon dioxide, sulfur dioxide and nitrogen oxide), the 

source and/or transport pathways, exposure media, exposure point, biological receptor types and 

effects endpoints of potential concern. 

26
The stressor resulting from application of gas cartridges applied to sealed burrows in open fields, 

rangeland, lawns, golf courses, non-crop areas or re-forested areas are gases, such as carbon 

monoxide, formed after the ignition of the cartridges. The source is the cartridge applied to the 

site (burrows or dens); the exposure media is inhalation of gases that disperse or diffuse (carbon 

monoxide, sulfur dioxide, and other gases that may be inhaled by terrestrial animals that inhabit 

burrows, including both, vertebrates and invertebrates), resulting in death by asphyxiation 

leading to reduced survival, changes in the food chain due to reduced prey, and/ or changes in 

habitat integrity. Modifications of PCEs are expected, due to reduction in prey or modification 

of habitat. The label indicates that the burrows are to be sealed quickly after the cartridge is 

activated and inserted into the burrow, so the gases remain for an extended period of time inside 

the burrow. Exposure is expected to be minimal, except for burrowing animals. 

27
Fig. 2.1. Conceptual Model for Cartridge Products Containing Carbon, Sawdust, Sodium 

Nitrate, Potassium Nitrate and Sulfur 

Food chain 

Reduction in prey and food

Modification of PCEs 

 related to prey availability 

Terrestrial 

Vertebrates found 

in burrows at the 

time of application 

Cartridge is applied to use site; sawdust, carbon, sodium nitrate, potassium 

Stressor nitrate and sulfur; combustion by-products are produced 

Source 

Exposure Route 

Application 

burrow/ den

Inhalation of gas 

by-products 

Receptors 

Terrestrial 

Invertebrates found in 

burrows at the time of 

application

Attribute 

Change 

Individual 

organisms 

Reduced survival 

Reduced growth 

Reduced reproduction

Habitat integrity 

Reduction in primary productivity

Community change 

Modification of PCEs related 

 to habitat 

28
2.10 Analysis Plan 

In order to address the risk hypothesis for Registration Review, the potential for direct effects to 

non-listed species and direct and indirect effects to listed species is estimated. In the following 

sections, the use, environmental fate, and ecological effects of carbon, sawdust, potassium 

nitrate, sodium nitrate, and sulfur cartridges are characterized and integrated to assess the risks. 

No RQs were calculated due to the waiver of fate and toxicity data. Risk will be determined by 

lines of evidence including method of application, mode of action and life history characteristics 

reported in the risk description section. 

A refined risk assessment under the San Francisco Bay litigation will also be conducted for the 

California whipsnake, the San Francisco garter snake and the San Joaquin kit fox. Routine 

procedures for refined assessments for the litigation assessment are provided in Attachment I. 

However, the determinations are based on lines-of-evidence such as fate and transport 

characteristics and life history traits, with no modeling performed. 

2.10.1 Measures to Evaluate the Risk Hypothesis and Conceptual Model 

Measures of Exposure 

There are no relevant fate or monitoring data for individual active ingredients or mixtures, 

related to the gas cartridge products. No measures of exposure based on aquatic and terrestrial 

models predicting estimated environmental concentrations (EECs) for carbon, sawdust, 

potassium nitrate, sodium nitrate and sulfur cartridges using the maximum-labeled application 

rates and methods of application are derived due to the absence of data and type of exposure. 

However, the by-products (certain toxic gases such as carbon monoxide, carbon dioxide, sulfur 

dioxide and nitrogen oxide) may be transported via diffusion throughout the burrows. Runoff 

and spray drift are not expected to be potential transport mechanisms to the aquatic and 

terrestrial habitats. In this assessment, transport of cartridge by-products through diffusion (not 

through runoff or spray drift) is considered. Quantitative estimates of cartridge by-product 

exposure to non-target and endangered species, their prey and habitats are not derived (see also 

Section 3.2). 

Measures of Effect 

One-hundred percent mortality is assumed to occur at the application site from the combustion 

products resulting in asphyxiation. This estimate is based on various efficacy studies and other 

articles in the open literature, the mode of action and the expected exposure of non-target 

organisms in burrows or dens (see Section 3.2). Efficacy studies support the assumption of 

100% mortality, although it is conservative (refer to Appendix A for details). 

Integration of Exposure and Effects 

Risk estimation (Section 5.1) is the integration of exposure and ecological effects to determine 

the potential ecological risk from agricultural and non-agricultural uses of carbon, sawdust, 

29
potassium nitrate, sodium nitrate, and sulfur cartridges, and the likelihood of direct effects to 

non-listed species in terrestrial habitats. For the assessment of carbon, sawdust, potassium 

nitrate, sodium nitrate, and sulfur cartridge risks, the risk quotient (RQ) method is not used to 

compare exposure and measured toxicity values due to the waiver of data for fate and ecological 

effects. Other lines of evidence (i.e. presence of combustion by-products due to application 

method, mode of action) are used to characterize the risk to non-listed and listed species. 

The conclusion (Section 7) summarizes potential direct effects on non-listed and direct and 

indirect effects on listed species arising from FIFRA regulatory actions under Registration 

Review regarding the use of carbon, sawdust, potassium nitrate, sodium nitrate and sulfur in 

fumigant gas producing cartridge products. The conclusions relative to the Alameda whipsnake, 

the San Francisco garter snake and the San Joaquin kit fox are also presented in section 7. 

3. Exposure Assessment 

Carbon, sawdust, sodium nitrate, potassium nitrate and sulfur are formulated as gas 

cartridges for use in active burrows or dens for the target pests. All the five active 

ingredients are naturally occurring substances whose physical properties are well understood. 

In addition to the cartridge use, sulfur has agricultural uses that are not assessed in this 

document. The purpose intended for products containing these active ingredients is to kill 

certain vertebrate species inhabiting burrows or dens. These cartridges are lit and placed in 

burrows which are rapidly sealed, to produce toxic gases that kill the animals present at the 

site by asphyxiation. Pest species are not exposed to the active ingredients, but to the product 

of their combustion. Examples of such products are carbon monoxide, nitrogen oxide and 

sulfur dioxide. The active ingredients are not considered as stressors, but the gas-phase byproducts are considered the stressors. 

3.1 Label Application Rates and Intervals 

There are six labels for carbon, sawdust, sodium nitrate, potassium nitrate and sulfur, 

formulated as gas cartridges (Table 2.1). It is noted that sawdust and carbon products are coformulated with sodium or potassium nitrate and, in various formulations, with sulfur. The 

formulated product labels legally limit the chemicals’ potential use to only those sites and 

uses that are specified on the labels. 

Current target pests of carbon, sawdust, sodium nitrate, potassium nitrate and sulfur 

cartridges are stated in Table 2.1. Actual use information and usage data for carbon, sawdust, 

sodium nitrate, potassium nitrate and sulfur cartridges are provided in Section 2.4.3. 

Five label rates reflect the percent active ingredient range of 44-54% identified in the 1993 

Biological Opinion for five of the six labels. The sixth formulation, Revenge Rodent Smoke 

Bomb, has an active ingredient percentage of 38.8. 

3.2 Terrestrial Animal Exposure Assessment 

There are no EFED models currently in use to assess the exposure of terrestrial species living in 

burrows, for substances such as carbon, sawdust, sodium nitrate, potassium nitrate and sulfur, 

30
which are formulated in cartridges. The purpose of the gas cartridges is to treat burrows or dens 

with active target pests. The burrows or dens are sealed following application, and the toxic 

gaseous by products, are anticipated to exist at high concentrations and (a) be absorbed or 

entrapped by the soil, where (b) they are metabolized by soil microorganisms or (c) enter their 

elemental cycles, while the remainder may be (d) slowly lost to the environment (see Ramey et 

al. 1994, citing USDA 1994) and/ or diffuse/ disperse into the atmosphere afterwards. Based on 

the use pattern for the active ingredients, their by-products are expected to be in the sealed 

burrows or dens in substantial (lethal) amounts (a conservative assumption of 100% mortality is 

made). A high level of acute (short term) exposure is presumed for non-listed and listed 

terrestrial vertebrate and invertebrate animals living in burrows or dens, based on the label 

review results (use pattern), and findings of various efficacy studies that show high levels of 

mortality for most of the organisms tested (e.g., refer to Savarie, et al, 1980; Matschke, et al.

1980; Fagerstone, et al. 1981; Matschke and Fagerstone, 1984; Zhi and Chang, 1986; Matschke, 

et al. 1995, and refer to Appendix A, for further details about these studies). No terrestrial 

modeling will be conducted but exposure is presumed for non-listed and listed organisms living 

in treated burrows. No potential transport from spray drift or run-off is expected from the use of 

gas producing cartridges. 

For terrestrial non-listed and listed species that do not inhabit burrows or dens, no measurable 

exposure is expected to the cartridges toxic by-products, based on the use pattern derived from 

the label, used only in burrows or dens. 

3.3 Terrestrial Plant Exposure Assessment 

No direct exposure to terrestrial plants is anticipated, based on the burrow or den use pattern for 

the chemicals. The TerrPlant model will not be utilized. 

4. Effects Assessment 

The toxicity studies for the active ingredients used in the cartridges were waived. This 

assessment is limited to mixtures of carbon, sawdust, potassium nitrate, sodium nitrate and sulfur 

in the cartridges. A conservative estimate of one-hundred percent mortality is assumed based on 

the direct effects from the combustion products. Therefore no sub-lethal effects are evaluated. In 

addition, no ECOTOX data for individual active ingredients will be used in the assessment. 

Although no ECOTOX studies were used in the assessment, references are provided for carbon 

and carbon dioxide in Appendices J-M and for inorganic nitrates in Appendices N-P. The 

ECOTOX rejection codes are defined in Appendix Q. In addition to the reference list, a 

spreadsheet noting specific toxicity testing details including duration, endpoints and 

concentrations, is presented in Appendix R for carbon and S for inorganic nitrates. 

A review of the EIIS and AIMS databases for major and minor aggregate ecological incidents 

involving carbon, sawdust, potassium nitrate, sodium nitrate, and sulfur cartridges was 

completed on November 30, 2009. There were no cartridge product terrestrial incidents reported 

in the EIIS or AIMS databases for birds. The EIIS database recorded no major incidents for 

mammals or terrestrial invertebrates. No minor incidents were reported in the 6(a)(2) database 

for the gas cartridges. 

31
5. Risk Characterization 

5.1 Risk Estimation 

Acute and chronic RQs are usually compared to the Agency’s levels of concern (LOCs) to 

identify instances where the chemical’s use within the action area has the potential to adversely 

affect the non-target organisms. RQs may also be used to evaluate the potential impact on listed 

species via direct toxicity or indirectly based on direct effects to their food supply and their 

designated critical habitat. 

A conservative estimate of one-hundred percent mortality at the application site is expected from 

asphyxiation due to the combustion products. This assumption is realistic based on the use 

pattern, the mode of action, and various efficacy studies (refer to Appendix A for a brief 

summary of such studies). 

5.2 Risk Description 

5.2.1 Lines-of-evidence

No modeling was conducted and no incidents were reported for the cartridges. The impact of 

using the cartridges was based on the pesticide’s method of application and mode of action. In 

addition, ecological characteristics of non-listed and listed species were combined with 

information from the USFWS memos, a Biological Opinion (1993) and a 1996 letter concurring 

with EPA Region IX’s NLAA determination for the SFGS and SJKF (Attachment IV). 

USFWS Memos

 

There were four memos discussing the effects of the cartridges on listed species and one 

Biological Opinion (1993). One memo (010, 1981) addressed the gas fumigant magnesium 

phosphide, but was later extended to registered gas fumigants under memo (023, 1982). The 

request covered six listed species: black-footed ferret (Mustela nigripes), Eastern indigo snake 

(Drymarchon corais couperi), San Joaquin kit fox (Vulpes macrotis mutica), Utah prairie dog 

(Cynomys parvidens), blunt-nosed leopard lizard (Gambelia Crotaphytus silus) and the desert 

tortoise (Gopherus agassizil) and its critical habitat The opinion concludes that these species 

will be adversely affected by the use of these products and the only means of mitigating jeopardy 

is to restrict use in areas where the species are found. 

Another memo (016, 1981) required changes for the endangered species language on the label 

for sodium nitrate gas cartridges. Accordingly, the new label restricts use in areas where red 

wolves, gray wolves, and the San Joaquin kit fox may have dens. 

Memo (023, 1982) responded to a request for informal consultation for a label review of gas 

cartridges used in burrow fumigation and the impact on the black-footed ferret (Mustela 

nigripes), Eastern indigo snake (Drymarchon corais couperi), San Joaquin kit fox (Vulpes 

macrotis mutica), Utah prairie dog (Cynomys parvidens), blunt-nosed leopard lizard (Gambelia 

32
Crotaphytus silus) and the desert tortoise (Gopherus agassizil) and its critical habitat. The memo 

indicates that inclusion of endangered species language from previously approved gas cartridges 

for those species will avoid jeopardy. 

The fourth memo 036 (1984) responded to a request for review of previous biological opinions 

on prairie dog toxicants including gas cartridges. To preclude jeopardy for the black-footed 

ferret, a pre-control survey must be conducted in accordance with approved USFWS methods. If 

no signs of ferret presence are found, the pesticide may be used. If signs of ferret presence are 

found, consultation is required for case-by-case opinions. This requirement must be included on 

all prairie dog toxicant labels.

Biological Opinion 

The 1993 Biological Opinion covered seventeen listed species: black-footed ferret (Mustela 

nigripes), Eastern indigo snake (Drymarchon corais couperi), San Francisco garter snake 

(Thamnophis sirtalis tetrataenia), San Joaquin kit fox (Vulpes macrotis mutica), Utah prairie dog 

(Cynomys parvidens), Hualapai Mexican vole (Microtus mexicanus hualpaiensis), Point Arena 

mountain beaver (Aplodontia rufa nigra), Fresno kangaroo rat (Dipodomys nitratoides exilis), 

giant kangaroo rat (Dipodomys ingens), Stephens kangaroo rat (Dipodomys stephensi), tipton 

kangaroo rat (Dipodomys nitratoides nitratoides), Morro Bay kangaroo rat (Dipodomys 

heermanni morroensis), blunt-nosed leopard lizard (Gambelia Crotaphytus silus), Coachella 

Valley fringe-toed lizard (Uma inomata), island night lizard (Xantusia riversiana), Gopher 

Tortoise (Gopherus polyphemus), and the desert tortoise (Gopherus agassizil) and its critical 

habitat. Jeopardy calls for mammals were made for the Black-footed ferret, the Fresno kangaroo 

rat, Hualapai Mexican vole, Giant kangaroo rat, Morro Bay kangaroo rat, Stephen’s kangaroo 

rat, Tipton kangaroo rat, Point Arena Mountain beaver and the San Joaquin kit fox. A no 

jeopardy call was made for the Utah prairie dog. Jeopardy calls for reptiles were made for the 

blunt-nosed leopard lizard, Eastern indigo snake, the gopher tortoise and the San Francisco garter 

snake. A no jeopardy call was made for the Coachella Valley fringe-toed lizard, the desert 

tortoise and the Island night lizard. 

For species identified with jeopardy calls, alternatives are proposed to reduce or avoid jeopardy. 

No incidental take is allowed for the Black-footed ferret. Ferret surveys by trained staff are 

requested based on colony size. A proposal for EPA to maintain records on amount of acres 

controlled or the amount of chemical sold is included in the BO. 

The alternatives for the San Joaquin kit fox, Point Arena mountain beaver, Fresno kangaroo rat, 

the giant kangaroo rat and the Tipton kangaroo rat include limiting use to qualified individuals 

within the occupied habitat. An unquantifiable level of incidental take may occur even with the 

implementation of the alternatives. Therefore to minimize anticipated take, EPA must establish a 

monitoring enforcement program. The alternatives for the blunt-nosed leopard lizard and the San 

Francisco garter snake also limit the use of the cartridges to trained staff and request the 

monitoring program but also include restrictions on use during the lizard inactivity period unless 

approved by the USFWS. 

33
The alternatives for the Stephen’s kangaroo rat include either allowing no use in the occupied 

habitat or only allowing trained staff to use the cartridges in occupied habitat. No incidental take 

is anticipated or authorized following implementation of the alternatives. 

The alternatives for the Hualapai Mexican vole, the Morro Bay kangaroo rat, the Gopher 

tortoise, the Eastern indigo snake include no use in the occupied territory. With implementation 

of the alternative measures, no incidental take is allowed. The Gopher tortoise also allows no 

incidental take with the implementation of no use in the occupied habitat, but lists geographical 

restrictions for the habitat description. 

The California Department of Pesticide Regulation (Cal DPR) is established as a non-federal 

representative for purposes of conducting consultation with the US Fish and Wildlife Service, up 

to and including informal consultation. Informal consultation may be conducted where a 

determination is made by the action agency (or their non-federal representative) that an action is 

“Not Likely to Adversely Affect” a listed species. At the request of Cal DPR, EPA Region 9 

requested the US Fish and Wildlife Service review bulletins put in place by Cal DPR, for the 

protection of listed species and to concur that those bulletins were adequate replacements for the 

RPA’s indicated in the 1993 BO relative to certain species, including the SFGS and SJKF, and 

burrow fumigants. On November 1, 1996 the US Fish and Wildlife Service responded indicating 

that the Cal DPR bulletins were in fact, adequate and could substitute for the RPAs in the 1993 

BO relative to the species and burrow fumigants covered in that BO. The letter further indicated 

that species not covered in the BO or the effect of pesticides not covered in the BO, such as the 

CAW, would require further consultation. 

Life Histories for the California Alameda Whipsnake (CAW), the San Francisco Garter 

Snake (SFGS) and the San Joaquin Kit Fox (SJKF)

The CAW, SFGS and SJKF are addressed in the Registration Review and the SFB litigation. In 

addition to the USFWS memos and the Biological Opinion, life history information will be used 

to support the determinations. The cartridges are used on target small mammals that live in 

burrows or dens, therefore the life histories for the CAW, SFGS and SJKF were reviewed to 

determine use of burrows or dens for shelter or reproduction. 

There is a report noting the use of burrows as shelter for the CAW, which would indicate 

potential effects from the use of the gas cartridges. The most common types of shelter reported in 

grassland and scrub communities were small rodent burrows and rock crevices (USFWS, 2002; 

Appendix T). The CAW is the only species under the San Francisco Bay litigation designated as 

having critical habitat (Appendix U). The habitat was designated for the CAW on October 2, 

2006 (USFWS, 2005 and 2006) using the PCE’s summarized in Appendix V. 

The life history for the SFGS reports the use of mammal burrows which would indicate potential 

effects from the use of the cartridges (Appendix W). SFGSs may be found in densely vegetated 

ponds near open hillsides, which allow them to sun themselves, feed, and find shelter in rodent 

burrows (USFWS, 1985; USFWS, 2007; NatureServe, 2007). SFGSs may also hunt prey 

(amphibians) in rodent burrows during the summer (Goals Project, 2000). 

34
The life history characteristics for the SJKF indicate the use of burrows indicating a potential 

impact from cartridge use (Appendix X). SJKFs may use dens for shelter from adverse 

environmental conditions, reproduction, and escape from predators (USFWS, 1998 and 2008). 

Although kit foxes may dig their own dens, they may also modify and use those already 

constructed by other animals (ground squirrels, badgers, and coyotes), or use human-made 

structures (culverts, abandoned pipelines, or banks in sumps or roadbeds) (USFWS, 1998 and 

2008). 

35
36

Table 5.1. Summary of Current Distribution, Habitat Requirements, and Life History Information for the Assesse

Listed Species1

Assessed 

Species Size Current Range Habitat Type 

Designated 

Critical 

Habitat?

Reproductive 

Cycle Diet

San Francisco 

Garter Snake 

(SFGS) 

(Thamnophis 

sirtalis 

tetrataenia) 

Adult 

(46-131 cm in 

length), 

Females – 227 g, 

Males – 

113 g; 

Juveniles – 2 g 

(Cover Jr. and 

Boyer, 1988) 

(18–20 cm in 

length) 

San Mateo 

County 

Densely vegetated 

freshwater ponds 

near open grassy 

hillsides; emergent 

vegetation; rodent 

burrows 

No Oviparous 

Reproduction2

Breeding: Spring (Mar. 

and Apr.) and Fall 

(Sept. to Nov.) 

Ovulation and 

Pregnancy: Late spring 

and early summer 

Young: Born 3-4 

months after mating 

Juveniles: frog

(Pacific tree fr

CRLF, and bul

depending on s

and insects 

Adults: prima

frogs (mainly 

CRLFs; also 

bullfrogs, toad

lesser extent ne

freshwater fish

invertebrates; i

and small mam

San Joaquin 

Kit Fox 

(SJKF) 

(Vulpes 

macrotis 

mutica) 

Adult 

~2 kg 

Alameda, 

Contra 

Costa, 

Fresno, 

Kern, 

Kings, 

Madera, 

Merced, 

Monterey, 

San 

Benito, 

San 

Joaquin, 

San Luis 

Obispo, 

Santa 

Barbara, 

Santa 

Clara, 

Stanislaus, 

Tulare and 

Ventura 

counties 

A variety of habitats, 

including grasslands, 

scrublands (e.g., 

chenopod scrub and 

sub-shrub scrub), 

vernal pool areas, oak 

woodland, alkali 

meadows and playas, 

and an agricultural 

matrix of row crops, 

irrigated pastures, 

orchards, vineyards, 

and grazed annual 

grasslands. Kit foxes 

dig their own dens, 

modify and use those 

already constructed 

by other animals 

(ground squirrels, 

badgers, and 

coyotes), or use 

human-made 

structures (culverts, 

abandoned pipelines, 

or banks in sumps or 

roadbeds). They 

move to new dens 

within their home 

range often (likely to 

avoid predation by 

coyotes) 

No, but has 

designated 

core areas 

Mating and conception: 

late December - March. 

Gestation period: 48 to 

52 days. 

Litters born: February - 

late March 

Pups emerge from their 

dens at about 1-month 

of age and may begin to 

disperse after 4 – 5 

months usually in Aug. 

or Sept. 

Small animals 

including black

hares, desert 

cottontails, mic

kangaroo rats, 

squirrels, birds

lizards, insects

grass. It satisfi

moisture 

requirements f

prey and does 

depend on fres

sources. 

CA Alameda 

Whipsnake 

(CAW) 

(Masticophis 

lateralis 

euryxanthus) 

3 – 5 ft Contra 

Costa and 

Alameda 

Counties 

in 

California 

(additiona

l 

occurrenc

es in San 

Joaquin 

and Santa 

Clara 

Counties) 

Primarily, scrub and 

chaparral 

communities. Also 

found in grassland, 

oak savanna, oak-bay 

woodland, and 

riparian areas. Lands 

containing rock 

outcrops, talus, and 

small mammal 

burrows. 

Yes Emerge from 

hibernation and begin 

mating from late March 

through mid-June. 

Females lay eggs in 

May through July. 

Eggs hatch from 

August through 

November. Hibernate 

during the winter 

months. 

Lizards, small 

mammals, nes

birds, other sna

including rattle
5.2.2 Risk Conclusions

The risk description synthesizes an overall conclusion regarding the likelihood of adverse 

impacts leading to direct effects for non-listed species and direct or indirect dietary effects 

determination (i.e., “no effect,” “may affect”) for listed species from the use of cartridges from 

outdoor terrestrial exposures. The agency determined that there was the potential for adverse 

direct effects from the application of the cartridges from the combustion products to non-listed 

birds, mammals and terrestrial invertebrates inhabiting burrows or dens. There is also the 

potential for adverse direct effects to non-listed reptiles and amphibians inhabiting burrows or 

dens because birds are used as surrogates for those species. The determination is based on 

asphyxiation from the combustion products formed after the cartridge is ignited in the burrow or 

den and the burrow or den is sealed to retain the gases at the site. 

An assessment is also conducted for effects on listed species. If there is a determination that 

there is a potential for direct or indirect effects on listed species, a “may affect” determination is 

made. Following a “may affect” determination for listed species and critical habitat, additional 

information is considered to refine the potential for exposure and effects, and the best available 

information is used to distinguish those actions that “may affect, but are not likely to adversely 

affect” (NLAA) from those actions that are “likely to adversely affect” (LAA) endangered 

species and its critical habitat. 

The criteria used to make determinations that the effects of an action are “Not Likely to 

Adversely Affect” the listed species and its designated critical habitat include the following: 

• Significance of Effect: Insignificant effects are those that cannot be meaningfully 

measured, detected, or evaluated in the context of a level of effect where “take” occurs 

for even a single individual. “Take” in this context means to harass or harm, defined as 

the following: 

 Harm includes significant habitat modification or degradation that results in 

death or injury to listed species by significantly impairing behavioral patterns 

such as breeding, feeding, or sheltering. 

 Harass is defined as actions that create the likelihood of injury to listed species 

to such an extent as to significantly disrupt normal behavior patterns which 

include, but are not limited to, breeding, feeding, or sheltering. 

• Likelihood of the Effect Occurring: Discountable effects are those that are extremely 

unlikely to occur. 

• Adverse Nature of Effect: Effects that are wholly beneficial without any adverse effects 

are not considered adverse. 

Although there is no fate or toxicity data available for modeling and no reported major incidents 

the Agency makes a “May Affect, LAA” determination for listed burrowing species (birds, 

mammals, insects, and reptiles and amphibians using birds as a surrogate) for survival as an 

acute direct effect based on asphyxiation from the combustion products. The effect from the 

application of the cartridges is localized to the application site based on the label instructions to 

seal the burrow or den following the application. Supporting evidence is based on habitat and 

diet life history information (Nature Serve, 2009) for taxa representing listed species identified in 

37
Appendix B. Additional supporting information is provided from a 1993 Biological Opinion as 

well as memos from the USFWS indicating potential risk to terrestrial mammals and reptiles 

without specific mitigation for each species identified. The BO identified mitigation for 17 

specific species. This information was included on two labels, the Gas Cartridge and the Large 

Gas Cartridge. Six of those identified listed species were also included on three labels (Dexol 

Gopher Gasser, Revenge Smoke Bomb and SMOKE’em). One label does not include specific 

listed species information (Giant Destroyer). 

Potential indirect effects of survival, growth and reproduction on reduction in prey for listed 

species also resulted in a “May Affect, LAA” for birds, mammals, reptiles and amphibians based 

on asphyxiation from the combustion products. The indirect effects from cartridge application 

are not limited to species inhabiting burrows or dens because some prey are included in the diets 

of listed species that do not inhabit burrows or dens. Supporting evidence is based on diet life 

history information for taxa representing listed species consuming prey with burrow/den habitats 

as reported by USFWS which are identified in Appendix C. 

Indirect effects also include potential habitat modification. Habitat modification is based on 

reduction in prey as well as changes in habitat used for shelter or reproduction. There is a 

“Habitat Modification” determination for listed birds, mammals, reptiles and amphibians based 

on reduction in prey based on a conservative estimate of 100% mortality from the combustion 

products as well as reduction in shelter. Shelter can be reduced due to sealing the burrow or den 

entrances following application of the cartridges, especially for species that use other animal 

burrows or dens rather than creating their own burrows or dens. Habitat Modification for 

terrestrial invertebrates is based on limiting access to the burrows or dens after the pesticide is 

applied through sealing entrances. The Habitat Modification for plants is based on potential for 

reduction in seed dispersal. Because mammals may transport seeds in their fur, dispersal may be 

reduced due to the number of mammals available in a geographic area. Supporting evidence is 

based on habitat life history information for taxa representing listed species consuming prey with 

burrow/den habitats as reported by USFWS which are identified in Appendix D. 

EPA previously requested the registrant to modify labels for the Gas Cartridge and the Large Gas 

Cartridge based on conclusions from the Biological Opinion (1993). The Biological Opinion 

identified 17 listed species with specific mitigation for each such as time of use and geographic 

boundaries. In addition, memos from USFWS indicated risk to identified mammals and reptiles 

and included mitigation specific to six identified species. Based on those memos, six listed 

species were included on labels for Dexol Gopher Gasser, SMOKE’em, and Revenge Smoke 

Bomb. Those modified labels provide the basis for the current assessment. Additionally, Cal 

DPR’s bulletins were deemed adequate replacements for RPAs listed in the 1993 BO for certain 

species in CA. Therefore, the species for which labeling was changed relative to the 1993 BO 

and those covered by the Cal DPR bulletins which also were addressed in the 1993 BO, 

including the San Francisco garter snake and San Joaquin kit fox, are adequately protected at this 

time from potential effects of the burrow fumigants being assessed here. Nonetheless, during 

consultation with the US Fish and Wildlife Service on other species potentially affected, EPA 

will confirm that the measures in place remain adequate and that the ranges of these species have 

remained constant since the 1993 BO and the 1996 letter to EPA Region 9. 

38
Consultation will be reinitiated with the U. S. Fish and Wildlife Service under Section 7 of the 

Endangered Species Act. A screening list of endangered species with the potential to be 

adversely impacted by potassium nitrate, sodium nitrate, carbon, sawdust and sulfur cartridges, 

including the California whipsnake, is provided in Appendices B, C and D. For the SFGS and 

the SJKF the use of cartridges is determined to “Not Likely to Adversely Affect (NLAA)”. The 

NLAA determination is based on the 1996 USFWS response to allow the use of Cal DPR 

bulletins as a replacement for RPA’s noted in the 1993 BO. The use of the subject pesticides is 

determined to have No Effect for all other species not included in Appendices B, C and D, and 

critical habitat. 

5.2.2 Assessment Endpoints for Endocrine Disruptor

As required under FFDCA section 408(p), EPA has developed the Endocrine Disruptor 

Screening Program (EDSP) to determine whether certain substances (including pesticide active 

and other ingredients) may have an effect in humans or wildlife similar to an effect produced by 

a “naturally occurring estrogen, or other such endocrine effects as the Administrator may 

designate.” The EDSP employs a two-tiered approach to making the statutorily required 

determinations. Tier 1 consists of a battery of 11 screening assays to identify the potential of a 

chemical substance to interact with the estrogen, androgen, or thyroid (E, A, or T) hormonal 

systems. Chemicals that go through Tier 1 screening and are found to have the potential to 

interact with E, A, or T hormonal systems will proceed to the next stage of the EDSP where EPA 

will determine which, if any, of the Tier 2 tests are necessary based on the available data. Tier 2 

testing is designed to identify any adverse endocrine related effects caused by the substance, and 

establish a dose-response relationship between the dose and the E, A, or T effect. 

Between October 2009 and February 2010, EPA issued test orders/data call-ins for the first 

group of 67 chemicals, which contains 58 pesticide active ingredients and 9 inert ingredients. 

This list of chemicals was selected based on the potential for human exposure through pathways 

such as food and water, residential activity, and certain post-application agricultural scenarios. 

This list should not be construed as a list of known or likely endocrine disruptors. 

Carbon, sawdust, sodium and potassium nitrates, and sulfur are not among the group of 58 

pesticide active ingredients on the initial list to be screened under the EDSP. Under FFDCA sec. 

408(p) the Agency must screen all pesticide chemicals. Accordingly, EPA anticipates issuing 

future EDSP test orders/data call-ins for all pesticide active ingredients. 

For further information on the status of the EDSP, the policies and procedures, the list of 67 

chemicals, the test guidelines and the Tier 1 screening battery, please visit our website: 

http://www.epa.gov/endo/ . 

5.3 Action Area Spatial Analysis 

In the case of a nationwide risk assessment conducted for Registration Review, the action area 

will encompass the entire U.S. and its territories. The purpose of defining the action area as the 

entire U.S. and its territories is to ensure that the initial area of consideration encompasses all 

areas where the pesticide may be used now and in the future, including the potential for off-site 

39
transport via spray drift and downstream dilution. Additionally, the concept of a nationwide 

action area takes into account the potential for direct and indirect effects and any potential 

modification to critical habitat based on ecological effect measures associated with reduction in 

survival, growth, and reproduction, as well as the full suite of sub-lethal effects available in the 

effects literature. 

It is important to note that the nationwide action area does not imply that direct and/or indirect 

effects and critical habitat modification are expected to or are likely to occur over the full extent 

of the action area, but rather to identify all listed species and critical habitat that may potentially 

be affected by the action. The Agency will use more rigorous analysis including consideration of 

available land cover data, toxicity data, and exposure information to determine areas where 

individual listed species and designated critical habitat may be affected or modified via 

endpoints associated with reduced survival, growth, or reproduction. 

The initial action area for the refined litigation assessment for the CAW, SFGS and the SJKF 

includes the entire state of California. However, due to the NLAA determination for the SFGS 

and the SJKF, The spatial analysis accounts for potential direct and indirect effects for the CAW 

based on the LAA determination from the use of the cartridges. A spatial analysis is provided in 

Appendix Y.

6. Uncertainties 

6.1 Exposure Assessment Uncertainties 

The screening-level risk assessment usually focuses on characterizing potential ecological risks 

resulting from a maximum use scenario, which is determined from labeled statements of 

maximum application rate and number of applications with the shortest time interval between 

applications. The frequency at which actual uses approach this maximum use scenario may be 

dependant on pest resistance, timing of applications, cultural practices, and market forces. It is 

noted that several of these items do not apply to cartridge products (e.g. application rate). 

Instead, cartridges are lit and applied to a number of cavities of the active burrows or dens, 

which are sealed. The intensity of the impact of the use of cartridge products may depend on the 

distribution of these cartridges in the field. 

During the problem formulation stage of the registration review, all the environmental fate data 

for the uses of gas cartridges were waived. This decision was based on the limited exposure 

expected to the active ingredients. At this time, there are no data on the environmental fate of 

the by-products. Not all the by-products have been identified. A degree of uncertainty exists on 

the lack of environmental fate data for these compounds; however, some information was 

inferred from the open literature, about the fate of the reaction by-products. 

Another factor affecting the level of exposure is the length and complexity of the treated 

burrows. This includes the burrow configuration, size and shape (see Matschke, Fagerstone & 

Elias 1980). If the burrow system is completely closed, the dead air may delay diffusion of the 

gases, and the toxicant may be lost through absorption by the soil lining the tunnel (see Matschke 

40
et al. 1995; please, note that the authors make a point that the soil lining is also moist, but see the 

next uncertainty). 

The soil moisture and texture have been identified as important factors affecting the survival of 

tested species in efficacy studies. Diffusion of the toxic gases may increase in dryer or porous 

soils, increasing the survival (Matschke & Fagerstone, 1984, see also label for Dexol Gopher 

Gasser, Reg. No. 192-49). The gases generated by the cartridges combustion disperse into the 

atmosphere or are absorbed in the soils, where they may undergo metabolization by soil 

microorganisms (Ramey et al., 1994, citing USDA, 1994). 

The length of the cartridge’s fuse may be a factor affecting non-target species survival, since a 

longer fuse would allow more time to seal the burrow (see Matschcke et al., 1980 and Fagerstone 

et al., 1981). 

The “size” of the cartridge may be a factor affecting the survival of non-target species present in 

the burrows. One study (Fagerstone et al., 1981) recommended the use of larger size cartridges 

(increasing the mass of the total active ingredients, but maintaining the same proportion), to 

improve their efficacy. In a follow up study (Matschke & Fagerstone, 1984) they tested the same 

species (Richardson’s ground squirrel, Spermophilus richardsonii) with a larger sized cartridge, 

with improved efficacy results.

There is also uncertainty in the use of the cartridges. It appears that the acreage treated with gas 

cartridges is usually relatively small, as suggested by an informational sheet from the Montana 

Department of Agriculture. According to the leaflet, available in the Internet, fumigants, such as 

cartridge products, “are effective tools for follow up of poison bait applications.” It further says 

that, “Burrow fumigants can also be used as a primary control technique although cost of 

materials and labor generally restrict their use to small acreages or sparse populations.” 

Hygnstrom & VerCauteren (2000) evaluated the effectiveness and cost of five burrow fumigants 

used to manage black-tailed prairie dogs: methyl bromide, chloropicrin, methyl bromidechloropicrin mixture, aluminum phosphide and gas cartridges. (At the present time, methyl 

bromide and chloropicrin are not registered for this use.). No difference in efficacy was found 

among treatment methods (≥95% reduction); but costs of aluminum phosphide and gas cartridges 

were around twice that for the other fumigants. 

Limitations for county level usage data obtained from California’s Department of Pesticide 

Regulation Pesticide use Report (CDPR) include only years that reported a methodology for 

removing outliers in terms of area treated and pounds applied. CDPR PUR documentation 

indicates that errors in the data may include the following: a misplaced decimal; incorrect 

measures, area treated, or units; and reports of diluted pesticide concentrations. In addition, it is 

possible that the data may contain reports for pesticide uses that have been cancelled. The 

CPDR PUR data does not include home-owner applied pesticides; therefore, residential uses are 

not likely to be reported (note that the cartridges should not be used in residential settings). As 

with all pesticide usage data, there may be instances of misuse and misreporting. The Agency 

made use of the most current information and in cases where there were discrepancies; the most 

conservative information was used. 

41
Publicly available data from the California Department of Pesticide Regulation was used to 

outline the pounds of carbon used for cartridges in California over the three most recent years 

available at the time the data was gathered (2003-2005). Uses reported in the CDPR PUR 

database include applications to parks, golf courses, cemeteries, rangeland, pastures, and along 

roadside and railroad rights-of-way. 

Publicly available data from the California Department of Pesticide Regulation was used to 

produce Table 2.3, outlining the pounds of sawdust used in California over the three most recent 

years. Only 0.143 to 1.417 lbs of sawdust were used from 2003 to 2005 in California, and they 

were mostly used for landscape maintenance and vertebrate control. 

For sulfur containing cartridges, the California Department of Pesticide Regulation (CDPR) use 

information data indicate that the use for “vertebrate control” in the period of 2003 to 2005 

ranged from 453 to 4418 lb. Sulfur has uses other than cartridges; therefore, the usage table is 

not included. 

6.2 Effects Assessment Uncertainties 

Efforts are made to select the organisms most likely to be affected by the type of compound and 

usage pattern; however, there is an inherent uncertainty in extrapolating across phyla. 

A conservative assumption of 100% mortality is assumed for any animal at the application site 

due to the combustion products associated with the use of carbon, sawdust, potassium nitrate, 

sodium nitrate and sulfur cartridges. This assumption is supported by various efficacy studies 

(refer to Appendix A). However, for certain species, it was found that the efficacy was lower 

(e.g. for badgers). For some species, there is the potential for an animal to avoid the effects of 

the cartridges based on behavioral cues. Some species (e.g. wood chucks and badgers) emerge 

from burrows when they are aware of any action to seal one of the entrances. The species habits 

may affect their survival. In Ramey (1995), a study performed with badgers, it was speculated 

that the test species could plug the burrow and dig away by backfilling the tunnel behind them; 

therefore, avoiding the gases.

The mortality or survival of target and non-target species present in burrows at the time of 

treatment may depend on the body weight of the species (Matschcke et al., 1980 and Fagerstone 

et al., 1981). 

No secondary toxicity from consumption of dead animals is expected for carbon monoxide 

cartridges, based on a study by Savarie et al., 1980; however, secondary toxicity for other gas 

cartridges is uncertain. 

7. Summary and Conclusions 

42
Ramey & Schafer (1996), described concisely the sodium nitrate plus carbon cartridge, as 

follows: “The gas cartridge is a pyrotechnic device and is composed of two parts: 1) the tube – a 

cardboard cylinder closed by cardboard caps at both ends containing the formulated product, 

predominantly sodium nitrate and charcoal; and 2) the fuse – a fireworks fuse inserted through 

one end cap into the combustible mixture and causes it to ignite. When the burning gas cartridge 

is used in a confined space with a limited air supply, such as a burrow or den, it can produce 

lethal concentrations of carbon monoxide.” This description is illustrative also of cartridges 

containing other active ingredients. 

The cartridges are designed to be ignited and burn, releasing toxic gases, such as carbon 

monoxide and sulfur dioxide, and other solid compounds. The active ingredients, carbon, 

sawdust, sodium nitrate, potassium nitrate and sulfur, are not the stressors. The stressors are the 

gases released after the combustion reaction. The inhalation of such toxic gases is the cause for 

asphyxiation of the target organism; therefore, the effect most likely to be observed, which 

occurs on a short time basis, is mortality. No substantial chronic or subchronic effects are 

expected. The effects of gas cartridge products should be confined within burrows or dens, and 

not outside of them. Eventually, the gases are dispersed in the environment or absorbed by the 

soil, where they are not expected to harm wildlife or the environment, while the solids byproducts remain in the burrows. One example of such a solid is sodium carbonate (Na2CO3), 

which is nearly inert and appears to be of low toxicity (rats LD50 of 4090 mg/kg, as per its 

MSDS). It is of no ecological effects concern. 

The gas cartridges are applied to active burrows in open fields, rangeland, lawns, golf courses, 

non-crop areas or re-forested areas, or dens in rangeland, crop and non-crop areas. The exposure 

media/source is gas diffusion (carbon monoxide, sulfur dioxide and/ or other gases that may be 

inhaled by terrestrial animals that inhabit burrows or dens), resulting in death by asphyxiation 

leading to reduced survival as the assessment endpoint for direct effects. The label indicates that 

the burrows or dens are to be sealed quickly after the cartridge is ignited and inserted into the 

burrow or den, so the gases remain at toxic (lethal) levels for a period of time inside the burrow 

or den. There are instructions describing soil conditions for optimum benefits from the cartridges 

used in burrows as well as instructions on sealing burrows and dens. 

An initial review is conducted to determine the potential effect on non-listed species from the use 

of cartridges from outdoor terrestrial exposures. The Agency determined that there was the 

potential for adverse direct effects from the application of the cartridges from the combustion 

products to non-listed birds, mammals and terrestrial invertebrates inhabiting burrows or dens. 

There is also the potential for adverse direct effects to non-listed reptiles and amphibians 

inhabiting burrows or dens because birds are used as surrogates for those species. There is no 

direct effect expected for terrestrial plants. The determinations are based on asphyxiation from 

the combustion products formed after the cartridge is ignited in the burrow or den and the burrow 

or den is sealed to retain the gases at the site. 

In fulfilling its obligations under Section 7(a)(2) of the Endangered Species Act, the information 

presented in this listed species risk assessment represents the best data currently available to 

assess the potential risks of carbon, sawdust, potassium nitrate, sodium nitrate and sulfur 

cartridge combustion products to listed species. If there is a determination that there is a 

43
potential for direct or indirect effects on listed species, a “may affect” determination is made. 

Following a “may affect” determination for listed species and critical habitat, additional 

information is considered to refine the potential for exposure and effects, and the best available 

information is used to distinguish those actions that “may affect, but are not likely to adversely 

affect” (NLAA) from those actions that are “likely to adversely affect” (LAA) endangered 

species and its critical habitat. 

The Agency makes a “May Affect, LAA” determination for listed burrowing species (birds, 

mammals, insects, and reptiles and amphibians using birds as a surrogate) for survival as an 

acute direct effect based on asphyxiation from the combustion products. The effect from the 

application of the cartridges is localized to the application site based on the label instructions to 

seal the burrow or den following the application. Supporting evidence is based on habitat and 

diet life history information for taxa representing listed species identified in Appendices B. 

Additional supporting information is provided from a 1993 Biological Opinion as well as memos 

from the USFWS indicating jeopardy to terrestrial mammals and reptiles with specific 

alternatives for each species identified. The BO identified alternatives for 17 specific species. 

This information was included on two labels, the Gas Cartridge and the Large Gas Cartridge. 

Six of those identified listed species were also included on three labels (Dexol Gopher Gasser, 

Revenge Smoke Bomb and SMOKE’em). One label does not include specific listed species 

information (Giant Destroyer). 

The BO also indicated that even with implementation of the alternatives, there was still risk for 

the San Joaquin kit fox, Point Arena mountain beaver, Fresno kangaroo rat, giant kangaroo rat, 

and Tipton kangaroo rat resulting in an unquantifiable level of incidental take. Although, the 

current labels reflect the need to limit use in the habitat of the Black-footed ferret, San Joaquin 

kit fox, Utah prairie dog, blunt-nosed leopard lizard, Eastern indigo snake and desert tortoise, the 

Agency will confirm these measures remain protective and that habitat range has not changed. 

Potential indirect effects of survival, growth and reproduction on reduction in prey for listed 

species also resulted in a “May Affect, LAA” for birds, mammals, reptiles and amphibians based 

on asphyxiation from the combustion products. The indirect effects from cartridge application 

are not limited to species inhabiting burrows or dens because some prey are included in the diets 

of listed species that do not inhabit burrows or dens. Supporting evidence is based on diet life 

history information for taxa representing listed species consuming prey with burrow/den habitats 

as reported by USFWS which are identified in Appendix C. 

Indirect effects also include potential habitat modification. Habitat modification is based on 

reduction in prey as well as changes in habitat used for shelter or reproduction. There is a 

“Habitat Modification” determination for listed birds, mammals, reptiles and amphibians based 

on reduction in prey based on a conservative estimate of 100% mortality from the combustion 

products as well as reduction in shelter. Shelter can be reduced due to sealing the burrow or den 

entrances following application of the cartridges, especially for species that use other animal 

burrows or dens rather than creating their own burrows or dens. Habitat Modification for 

terrestrial invertebrates is based on limiting access to the burrows or dens after the pesticide is 

applied through sealing entrances. The Habitat Modification for plants is based on potential for 

44
reduction in seed dispersal. Because mammals may transport seeds in their fur, dispersal may be 

reduced due to the number of mammals available in a geographic area. Supporting evidence is 

based on habitat life history information for taxa representing listed species consuming prey with 

burrow/den habitats as reported by USFWS which are identified in Appendix D. 

These determinations are based on lines of evidence using the best available information. The 

determinations are summarized in Tables 7.1 for the initial screen and 7.2 for the listed species. 

The determinations for the three species for which refinements have been made are presented in 

Table 7.3 and Table 7.4. 

Table 7.1. Potential Direct Effects on Non-Listed Species Inhabiting Burrows and 

Dens for the Use of Carbon, Sawdust, Potassium Nitrate, Sodium Nitrate and Sulfur 

Cartridges 

Species 

Assessment 

Endpoint Description of Results of Risk Estimation 

Burrowing Birds 

Burrowing 

Mammals 

Burrowing 

Reptiles 

Burrowing 

Amphibians 

Burrowing 

Terrestrial 

Invertebrates 

Survival There is a potential for acute direct adverse effects on burrowing 

species based on asphyxiation from the combustion products at 

the site of application. 

7.2 Effects on Listed Species for the Use of Carbon, Sawdust, Potassium Nitrate, 

Sodium Nitrate and Sulfur Cartridges 

45
Species 

Assessment 

Endpoint 

Effects 

Determination Description of Results of Risk Estimation 

Direct Effects 

Terrestrial 

(Juveniles and adults)

Burrowing 

Birds 

Burrowing 

Mammals 

Burrowing 

Reptiles 

Burrowing 

Amphibians 

Burrowing 

Terrestrial 

Invertebrates 

Direct Effects 

Survival of 

individuals 

via direct 

effects on 

terrestrial 

organisms 

May Affect 

LAA 

The determination for acute direct effects is 

based on 100% mortality from asphyxiation 

based on the combustion products following 

application. 

Indirect Effects 

Birds 

Mammals 

Reptiles 

Amphibians 

Survival of 

individuals 

via reduction 

of prey (i.e.,

birds, 

terrestrial 

mammals, 

reptiles, 

terrestrial 

phase 

amphibians 

and terrestrial 

invertebrates) 

May Affect 

LAA 

The determination for acute indirect effects is 

due to an inability to measure the effect for 

reduction in prey based on asphyxiation from 

the combustion products. The reduction in 

prey may affect both burrowing and nonburrowing listed species consuming animals 

with burrow/den habitats. 

 

Birds 

Survival of 

endangered 

Habitat Modification There is a “Habitat Modification” based on a 

reduction in prey from asphyxiation for both 

burrowing and non-burrowing species. 

46
7.2 Effects on Listed Species for the Use of Carbon, Sawdust, Potassium Nitrate, 

Sodium Nitrate and Sulfur Cartridges 

Species 

Assessment Effects 

Endpoint Determination Description of Results of Risk Estimation 

Mammals 

Reptiles 

Amphibians 

Terrestrial 

Invertebrates 

There is a “Habitat Modification” 

determination for burrowing species based on a 

reduction in cover/shelter. Use of the pesticide 

results in reduced access to burrows for shelter 

or reproduction. 

Terrestrial 

Plants 

species via 

effects on 

habitat (i.e.,

reduction in 

prey, shelter, 

riparian 

vegetation) 

There is a habitat modification determination 

for terrestrial plants based on the potential for 

reduction in seed dispersal. 

47
Table 7.3 Effects Determination Summary for Effects of Potassium and Sodium 

Nitrate Cartridges for Three Listed Species 

Species Effects 

Determination 

Basis for Determination 

Potential for Direct Effects

Terrestrial-phase (Juveniles and Adults): 

Habitats for the snake include shrub communities and adjacent 

habitats of grassland, savanna and oak-bay woodland. The 

most common types of retreat site in both the grassland and 

scrub communities are small rodent burrows and rock crevices, 

with brush piles, deep soil crevices and debris piles also used 

for cover/shelter. The determination for acute direct effects is 

based on 100% mortality from asphyxiation based on the 

combustion products following application if applied to a 

burrow in which the snake is residing during application. 

 

Potential for Indirect Effects

 Alameda 

Whipsnake 

(Masticophis 

lateralis 

euryxanthus) 

(CAW) 

May Affect, 

Likely to 

Adversely 

Affect (LAA) 

Terrestrial prey items, riparian habitat 

There is an “LAA” determination for acute indirect effects due 

to prey reduction for the CAW consuming lizards, snakes and 

small mammals that may inhabit burrows. The prey may be 

present at the site of application, which results in mortality for 

the prey. 

Potential for Direct Effects 

Terrestrial-phase (Juveniles and Adults): 

The SFGS uses densely vegetated ponds near open hillsides 

where they can sun themselves, feed, and find shelter in rodent 

burrows. Rodents are targets for nitrate cartridges. The 

determination for potential acute direct effects is based on 

100% mortality from asphyxiation based on the combustion 

products following application if applied to a burrow in which 

the snake is residing during application. US FWS has indicated 

measures put in place by Cal DPR are adequate protection for 

this species relative to uses of burrow fumigants. 

Potential for Indirect Effects 

 San Francisco 

Garter Snake 

(Thamnophis 

sirtalis 

tetrataenia)(SF

GS) 

May Affect, Not 

Likely to 

Adversely 

Affect (NLAA)1 

Terrestrial prey items, riparian habitat 

There is an “NLAA” determination for acute indirect effects 

due to prey reduction. The main diet of adult SFGS consists 

of California Red-Legged Frog (CRLF), which are listed as a 

threatened species (USFWS, 1985 and 2007). CRLFs also 

use small mammal burrows and moist leaf litter as habitat, 

and might be present at the time of application. US FWS has 

indicated measures put in place by Cal DPR are adequate 

protection for this species relative to uses of burrow 

fumigants. 

48
Table 7.3 Effects Determination Summary for Effects of Potassium and Sodium 

Nitrate Cartridges for Three Listed Species 

Species Effects Basis for Determination 

Determination 

Potential for Direct Effects 

Terrestrial-phase (Juveniles and Adults): 

The fox inhabits a variety of habitats, including grasslands, 

grazed grasslands, shrublands, meadows, and areas of row 

crops, orchards and vineyards (East Contra Costa County 

HCP/NCCP, 2006). Although kit foxes may dig their own 

dens, they also modify and use those constructed by other 

animals (ground squirrels, badgers, and coyotes). Coyotes and 

ground squirrels are both target pests. The determination for 

potential acute direct effects is based on 100% mortality from 

asphyxiation based on the combustion products following 

application at the application site. US FWS has indicated 

measures put in place by Cal DPR are adequate protection for 

this species relative to uses of burrow fumigants. 

Potential for Indirect Effects

San Joaquin Kit 

Fox (Vulpes 

macrotis mutica) 

(SJKF) 

May Affect, Not 

Likely to 

Adversely 

Affect (NLAA)1

Terrestrial prey items, riparian habitat 

There are potential acute indirect effects due to prey reduction 

for the SJKF consuming small mammals such as kangaroo rats, 

pocket mice, California ground squirrels and insects that may 

inhabit burrows. Some of the small mammals may also be 

target pests, such as ground squirrels. The prey may be present 

at the site of application, which results in mortality of the prey. 

However, USFWS has indicated measures put in place by Cal 

DPR are adequate protection for this species relative to uses of 

burrow fumigants. 

 

 

1

 This species was considered in the USFWS 1993 BO and was addressed relative to potassium and sodium nitrate 

cartridges in the USFWS 1996 letter to the EPA Region 9 office wherein the USFWS concurred that the Cal DPR 

Bulletins were adequate to address potential risk to the San Joaquin kit fox. The determination of NLAA is based 

upon the adequacy of the Cal DPR bulletin to protect this listed species. 

49
7.4. Effects Determination Summary for the Critical Habitat Impact Analysis

Designated 

Critical Habitat 

for: 

Effects 

Determination 

Basis for Determination 

 Almeda 

Whipsnake (CAW) 

Habitat 

Modification 

Lines-of-evidence indicate potential adverse effects for reduction in prey for 

the CAW consuming species inhabiting burrows. 

The PCEs for the CAW include mammal burrows as habitat. Because the 

application method involves closing the burrow openings after inserting the 

cartridge, there would be a reduction in available shelter/cover. 

EPA previously requested modification of labels for the Gas Cartridge and the Large Gas 

Cartridge based on conclusions from the Biological Opinion (1993). That BO identified 17 listed 

species with specific mitigation for each such as time of use and geographic boundaries. In 

addition, memos from USFWS indicated risk to identified mammals and reptiles and included 

mitigation specific to the six identified species. Based on those memos, six listed species were 

included on labels for Dexol Gopher Gasser, SMOKE’em, and Revenge Smoke Bomb. Those 

modified labels provide the basis for the current assessment. 

Based on the conclusions of this assessment, including additional listed species identified and the 

need to review geographic boundaries for current and previously identified listed species, 

consultation will be reinitiated with the U. S. Fish and Wildlife Service under Section 7 of the 

Endangered Species Act. A screening list of endangered species with the potential to be 

adversely impacted by potassium nitrate, sodium nitrate, carbon, sawdust and sulfur cartridges is 

provided in Appendices B-D. A ‘no effect” determination has been made for all other listed 

species and their critical habitat, not identified on the Appendices. 

50
8. References 

East Contra Costa County HCP/NCCP. 2006. San Joaquin Kit Fox (Vulpes macrotus mutica). 

Available online at: http://www.co.contracosta.ca.us/depart/cd/water/HCP/archive/hcp_nccp_content/hcp_nccp/app_figs/App%20D%20co

mponents/App_D-02a_San_Joaquin_kit_fox_profile_1-18-05.pdf (Accessed on April 3, 2008). 

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. 

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. 

Magran, S.J. No Date. A memorandum report: Development of rodenticide cartridge 

pyrotechnic production of carbon monoxide. Chemical Corps Technical Commands, Army 

Chemical Center, Maryland, 34 pp. (as cited by Savarie, et al. 1980). 

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. 

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, 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. 

Montana Department of Agriculture. “Controlling Burrowing Rodents with Burrow Fumigants.” 

Montana Department of Agriculture, Vertebrate Pest Program, Helena, Montana. Informational 

sheet available at the url: http://agr.mt.gov/weedpest/pdf/VertBulletins/BurrowFumigants.PDF 

NatureServe, 2007. Explorer. Available online at http://www. natrueserve.org . 

NatureServe, 2009. Explorer. Available online at http://www. natrueserve.org . (Accessed 2 

March 2010). 

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. 

51
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, C.A. and E.W. Schafer, 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. pp. 

219-224. 

Savarie, P.J., J.R. Tigner, D.J. Elias and Hayes. 1980. "Development of a Simple Two-Ingredient 

Pyrotechnic Fumigant," Proceedings Ninth Vertebrate Conference, Fresno, CAY pp. 215-221. 

U.S. Department of Agriculture. 1994. Animal Damage Control Program Final Environmental 

Impact Statement. APHIS. Washington, DC. Vol. 1-3, 1102 pp. (as cited by Ramey et al. 1994). 

U.S. Environmental Protection Agency. 1991. Environmental Fate and Ecological Risk 

Assessment for the Reregistration of Carbon and Carbon Dioxide. Office of Pesticide Programs, 

United States Environmental Protection Agency, Washington, DC. 

U.S. Environmental Protection Agency. 1991. Environmental Fate and Ecological Risk 

Assessment for the Reregistration of Nitrites/Nitrates (Sodium and Potassium Nitrates). Office of 

Pesticide Programs, United States Environmental Protection Agency, Washington, DC. 

U.S. Environmental Protection Agency. 1991. Environmental Fate and Ecological Risk 

Assessment for the Reregistration of Sulfur. Office of Pesticide Programs, United States 

Environmental Protection Agency, Washington, DC. 

U.S. Environmental Protection Agency. 1998. Guidelines for Ecological Risk Assessment. Risk 

Assessment Forum, Office of Research and Development, Washington, D.C. 011-965103024. 

EPA/630/R-95/002F. April 1998. 

U.S. Environmental Protection Agency. 2000. Risk Characterization Handbook. Science Policy 

Council, U.S. Protection Agency, Washington, D.C. 20460. EPA 100-B-00-002.

U.S. Environmental Protection Agency. 2004. Overview of the Ecological Risk Assessment 

Process in the Office of Pesticide Programs, U.S. Environmental Protection Agency. 

Endangered and Threatened Species Effects Determinations. Office of Prevention, Pesticides 

and Toxic Substances, Office of Pesticide Programs, Washington, D.C. January 23, 2004.

U.S. Environmental Protection Agency. 2005. Generic Format and Guidance for the Level I 

Screening Ecological Conducted in the Environmental Fate and Effects Division. Office 

Washington, D.C. January 24, 2005. 

U.S. Environmental Protection Agency. 2008. Problem Formulation for the Ecological Risk 

Assessment for Carbon Dioxide and Gas Fumigant Producing Cartridges: Carbon, Sawdust, 

Sodium Nitrate, Potassium Nitrate and Sulfur, U.S. Environmental Protection Agency Office of 

52
Prevention, Pesticides and Toxic Substances, Office of Pesticide Programs, Washington, D.C. 

March 18, 2008. 

U.S. Fish and Wildlife Service. 1981. Letter in Response to U. S. Environmental Protection 

Agency’s September 25, 1981 Telephone Request for a Review of All Prairie Dog Toxicants. U. 

S. Department of Interior, Fish and Wildlife Service (FWS/OES). 

U.S. Fish and Wildlife Service. 1982. Letter in Response to U. S. Environmental Protection 

Agency’s September 23, 1982, Request for Consultation for the Label Improvement Program of 

seven gas cartridges in burrow fumigation and the impact on the black-footed ferret (Mustela 

nigripes), eastern indigo snake (Drymarchon corais couperi), San Joaquin kit fox (Vulpes 

macrotis mutica), Utah prairie dog (Cynomys parvidens), blunt-nosed leopard lizard (Gambelia 

[Crotaphytus] silus) and the desert tortouise (Gopherus agassizii). U. S. Department of Interior, 

Fish and Wildlife Service (FWS/OES EPA-82-8). 

U.S. Fish and Wildlife Service. 1984. Letter in Response to U. S. Environmental Protection 

Agency’s May 31, 1984, Request for a Review of All Prairie Dog Toxicants. U. S. Department 

of Interior, Fish and Wildlife Service (FWS/OES EPA-84-9). 

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