U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2006-3092

June 2006

Toxicity of Sodium Bicarbonate to Fish from 

Coal-Bed Natural Gas Production in the Tongue and 

Powder River Drainages, Montana and Wyoming 

Printed on recycled paper

This study evaluates the sensitivity 

of aquatic life to sodium bicarbonate 

(NaHCO3), a major constituent of coalbed natural gas-produced water. Excessive amounts of sodium bicarbonate 

in freshwater streams and rivers may 

adversely affect the ability of fish to 

regulate their ion uptake. The study area 

includes the Tongue and Powder River 

drainages within the Powder River Basin 

in southeastern Montana and northeastern 

Wyoming. 

In the past decade, thousands of 

coal-bed natural gas wells have been 

drilled within the Powder River Basin, 

one of the largest sources of coal in the 

United States. The process of gas extraction involves drilling water wells into 

underground coal seams (fig. 1). Water 

from the aquifer is then drawn through 

the well, which decreases water pressure 

and releases the methane gas. The gas 

rises up the wellbore where it is collected 

and distributed via pipeline for various 

energy uses. The water becomes a waste 

product and, depending on local circumstances, is released to streams. Sodium 

bicarbonate is one of the constituents 

in the wastewater; it can reach levels 

over 1,000 mg/L (milligrams per liter). 

Neither the U.S. Environmental Protection Agency nor the State of Montana has 

established a sodium bicarbonate water 

quality criterion or standard for aquatic 

life. 

Sodium bicarbonate is not naturally 

present in appreciable concentrations 

within the surface waters of the Tongue 

and Powder River drainages and the large 

concentrations have been shown to be 

acutely toxic to native fish (Mount and 

others, 1997). In 2003, with funding and 

guidance provided by the U.S. Environmental Protection Agency, the Montana 

Fish, Wildlife, and Parks and the U.S. 

Geological Survey initiated a collaborative study on the potential effects of coalbed natural gas wastewater on aquatic 

life. A major goal of the study is to provide information to the State of Montana 

Water Quality Program needed to develop 

an aquatic life standard for sodium bicarbonate. The standard would allow the 

State, if necessary, to establish targets for 

sodium bicarbonate load reductions.

The collaborative study focuses 

on the acute and chronic toxicity of 

sodium bicarbonate on select fish species. 

Understanding the concentration at which 

sodium bicarbonate is toxic to fish provides the thresholds needed to establish 

water quality standards. In 2004, field 

assessments were added (fig. 2) to define 

the presence or absence of fish species in 

the target area, define additional species 

of interest for laboratory studies, and 

validate results found in the laboratory. 

Figure 2.  Researchers conduct field assessments to define the presence or

absence of fish in the Tongue and Powder River drainages, which flow from Wyoming

to Montana where they join the Yellowstone River. Extraction of coal-bed natural gas

in the area can release large amounts of sodium bicarbonate into the streams.

Figure 1.  Coal-bed natural

gas drilling in Montana.
Acute Toxicity

Acute toxicity experiments were 

designed to determine the median lethal 

concentration of sodium bicarbonate to 

fish (table 1). The experiments were 

conducted over a period of 96 hours. 

Fish were exposed to various amounts 

of sodium bicarbonate in simulated river 

water (fig. 3). Commercially-available 

salts were added to distilled or well 

water, which was formulated to represent the major ion composition of either 

the Tongue or Powder Rivers. The 

experiments were performed on early 

life stages (newly hatched and older fry) 

of fish native to the Tongue and Powder 

River drainages–fathead minnow, white 

sucker, and pallid sturgeon (fig. 4). 

Table 1.  Acute toxicity results indicate that the concentrations of sodium

bicarbonate that cause 50 percent of the exposed fish to die (LC50) are the

smallest in 4-day old fathead minnows in simulated Powder River water and pallid

sturgeon in simulated Tongue River water. Fathead minnows, pallid sturgeon, and

white sucker were all able to withstand greater amounts of sodium bicarbonate if

exposed after they were 21-days old.

Species

Age of 

fish in days 

(post-hatch)

Water being 

simulated

Sodium bicarbonate 

LC50 (+95%CI) 

(mg/L)

Fathead minnow 4 days Powder River 1,643 (1,188–2,377)

Fathead minnow 4 days Tongue River >4,000* 

Fathead minnow 39 days Tongue River 5,526 (5,057–6,038) 

White sucker 22 days Tongue River 5,121 (4,049–6,678) 

White sucker 22 days Powder River 5,421* 

Pallid sturgeon 4 days Powder River 1,158 (1,103–1,216)

Pallid sturgeon 4 days Tongue River 1,828 

*

Test did not meet EPA guidance for minimum number of organisms per test concentration.

Figure 3.  To study acute toxicity, fish fry

are exposed to different concentrations

of sodium bicarbonate in simulated river

water over a 96-hour period.

Chronic Toxicity

Flow-through experiments were 

conducted in the laboratory to determine long-term or delayed toxic effects 

of sodium bicarbonate on fish. These 

experiments had continuous supplies of 

water that allow fish to survive and grow 

over long periods of time. Water quality 

parameters were controlled so the effects 

due only to sodium bicarbonate could be 

isolated (fig. 5). 

To date, three chronic studies have 

been performed, two on the fathead minnow and one on the white sucker (fig. 4). 

Laboratory water was simulated to mimic 

the Tongue River (the control). Sodium 

bicarbonate was added in varied mg/L 

concentrations to the control water. The 

fish were exposed from fertilization until 

43 or 60 days post-hatch. 

Fertilized eggs were used to initiate 

the studies and continued though post 

swim-up. Because the small size of 

fathead minnow and white sucker eggs 

makes the exact number of eggs difficult 

to assess, the calculated percent hatch for 

control and experimental concentrations 

was estimated and statistical analyses 

were not performed on the data. White 

sucker are not a typical species used in 

laboratory experiments; the eggs were 

collected from wild fish and the percent 

hatch was consequently small (table 2). 

Because most of the treatments 

caused significant mortality during 

Experiment 1 for fathead minnows, a second experiment was conducted to include 

additional treatments and better define the 

Table 2.  Estimated percent hatch for the

native fathead minnows and white suckers

exposed to sodium bicarbonate in simulated

Tongue River water for chronic toxicity tests.

Sodium 

bicarbonate 

treatment

(mg/L)

Estimated hatch 

(percent)

Fathead 

minnow

White 

sucker

Control 63 23

 500* 78 21

 800 69 29

1,100 70 NA

1,400 44 30

*

 Concentration was 450 mg sodium bicarbonate per 

liter during white sucker experiment. (Continued on page 3)

Mont. Fish, Wildlife, & Parks

Mont. Fish, Wildlife, & Parks

A

Nebr. Game & Parks Commission

C

B

Figure 4.  Fish

native to the Tongue and

Powder River drainages were

used for experiments. A, The

fathead minnow (Pimephales 

promelas). B, The white

sucker (Catostomus commersonii), which is not normally

used as a laboratory animal,

but is very prominent in the

study area. C, The pallid

sturgeon (Scaphirhynchus 

albus), an endangered species

that inhabits the Yellowstone

River. 

2
point where significant mortality of fathead 

minnows might occur (table 3). White 

suckers appeared to tolerate greater concentrations of sodium bicarbonate than 

fathead minnows. No additional chronic 

experiment was conducted with white 

suckers. 

Results of the chronic experiments 

indicated that survival in fathead minnows was significantly less than the controls in all sodium bicarbonate concentrations above 400 mg/L (table 3); however, 

in the treatments without significant 

mortality, growth was not affected. Early 

survival for white suckers appeared to be 

unaffected. 

Table 3.  Percent survival of fish exposed to sodium bicarbonate in laboratory water simulating the Tongue River.

[m/L, milligrams per liter; h, hour; d, day]

Experiment 1, fathead minnow survival

 (percent)

Experiment 2, fathead minnow survival

 (percent)

Experiment 3, white sucker survival

 (percent)

Treatment 

(m/L) 96-h 0-30-d 30-60-d Treatment(m/L)

96-h 0-30-d 30-60-d Treatment

(m/L)

96-h 0-25-d 25-43-d

Control 94 89 96 Control 90 67 99 Control 64 54 69

 500 83 64 93 300 93 35 100 450 84 80 72

 800 55 33 + 400 90 57 100 800 90 53 82

1,100 40 21 + 625 60 30 100 ---- ---- ---- ----

1,400 8 2 + ---- ---- ---- ---- 1,400 94 52 45

Chronic Toxicity (continued)

Field Studies

Field sampling began in July 

2004 to determine fish species distribution at 15 selected sites in the Tongue 

and Powder River drainages and to 

evaluate the 

influence of 

water quality 

and habitat on 

fish species 

assemblages 

(table 4). Fish 

were collected 

by seining or 

electrofishing 

a 300-meter 

section of 

stream at each site. Fish and habitat 

measurements were collected to allow 

(1) the creation of a list of expected 

fish species at each site as predicted 

by the Warmwater Stream Assessment 

method (Quist and others, 2004), and 

(2) the calculation of an Index of Biological Integrity (Bramblett and others, 

2003) for each site. Because the white 

sucker was one of the most prominent 

species present during the field sampling, it was subsequently used in the 

chronic toxicity study.

In 2005, funds were provided to 

the Montana Fish, Wildlife, and Parks 

and the USGS in Cheyenne, Wyoming 

to collect water quality data in 

conjunction with fish and habitat 

surveys being conducted in the Tongue, 

Powder, and Rosebud Creek drainages. 

These data will be combined with the 

2004 survey data in order to create 

a database of fish species tolerances 

relative to levels of sodium bicarbonate 

and specific conductivity. 

Figure 5.  Chronic toxicity

experiments were conducted in the

laboratory “diluter,” which mimics

conditions in the Tongue River and allows

for the study of various concentrations of

sodium bicarbonate on fish. A, The grey

tanks held the fish; simulated Tongue

River water was added to some of the

tanks as the “control” for comparisons. 

B, The remainder of the tanks received

“exposure” waters, which consisted

of various concentrations of sodium

bicarbonate that were electronically

metered into glass mixing chambers at

the front of the diluter and added to the

simulated Tongue River water. 

A

As concentration and exposure time 

increased, so did the occurrence and 

severity of microscopic lesions in fathead 

minnows. After 60 days, fathead minnows from the 500 mg/L treatment had 

slightly increased incidence of kidney 

damage compared to the controls as 

defined by the greater number of regenerating tubules and focal degeneration 

that were observed in the kidneys of 

fish exposed to 500 mg/L. The histology examinations and compilation of 

growth data for white sucker are not yet 

complete. In addition to measurements 

of survival, growth, and histology, Na/K 

ATPase activity, and whole body ion 

contents are being determined to provide 

insight into how sodium bicarbonate 

might cause deaths of fish. 

+

 Sacrificed concentrations at day 37

B

3
Acknowledgements

This work was funded by the U.S. Environmental Protection Agency with matching funds from Montana Fish, Wildlife, 

and Parks and the USGS. Brady Morris 

and Joseph Meyer, University of Wyoming, Brad Mueller, USGS, and Kurt Hill, 

Montana Fish, Wildlife, and Parks provided 

professional and technical assistance. 

Findings to Date

It appears that within 96 hours, 

concentrations of sodium bicarbonate 

of 1,100 to 1,600 mg/L will cause 50 

percent mortalities in early lifestage 

fish under the Tongue or Powder River 

conditions. The concentration is reduced 

to 780 mg/L if fathead minnows are 

exposed to sodium bicarbonate shortly 

after fertilization rather than at 4-days 

old. Furthermore, significant mortalities 

of greater than 30 percent will occur if 

fish in the Tongue River are exposed to 

400 mg/L of sodium bicarbonate for 30 

days. Fathead minnows appear to be the 

most sensitive species followed by pallid 

sturgeon and then white suckers. 

References Cited

Bramblett, R.G., Johnson, T.R., Zale, A.V., 

and Heggem, D., 2003, Development of 

biotic integrity indices for prairie streams 

in Montana using fish, macroinvertebrate, 

and diatom assemblages: Bozeman, 

Mont, Montana Coop Fishery Research 

Unit.

Mount, D.R., Gulley, D.D., Hockett, J.R., 

Garrison, T.D., and Evans, J.M., 1997, 

Statistical models to predict the toxicity of 

major ions to Ceriodaphnia dubia, Daphnia magna, and Pimephales promelas

(fathead minnows): Environmental Toxicology and Chemistry 16, p. 2009-2019. 

Quist, M.C., Hubert, W.A., and Rahel, F.J., 

2004, Warmwater stream assessment 

manual: Cheyenne, Wyo., Wyoming 

Game & Fish Department, Fish Division.

Future Directions

We will continue to prepare a database that defines the toxicity of sodium 

bicarbonate to fish and other aquatic 

organisms in the Tongue and Powder Rivers. These data can then be used by Federal and State agencies to define water 

quality criterion for sodium bicarbonate. 

The field data that describes fish presence or absence will be interpreted with 

the laboratory results and the ongoing 

monitoring data currently being gathered 

by USGS to describe fish tolerances in 

Table 4.  General water chemistry, number of species, and number of fish observed during field assessments of 15 sites in the Tongue and

Powder River drainages.

[R, river; m, meter; 0C, degrees Celsius; mg/L, milligrams per liter, μs/cm, microSiemens per centimeter; s.u., standard units; CaCO3, calcium carbonate]

Site Date

Mean 

width 

(m)

Thalwag 

depth 

(m)

Temperature

(

o

C)

Oxygen

(mg/L)

Conductivity

(μs/cm)

pH

(s.u.)

Akalinity

(mg/L as

CaCO3)

Number of 

fish 

(species)

Number of 

fish

(individuals)

Powder R at Locate 7/25/2004 8.34 0.077 30.1 7.00 2,950 8.37 309 5 468

Little Powder R nr Broadus 7/24/2004 7.89 0.66 20.6 8.51 1,730 8.76 430 10 783

Powder R nr Moorhead 7/24/2004 32.60 0.26 15.7 8.21 2,295 8.35 163 5 246

Powder R at Sussex 7/21/2004 13.40 0.21 29.6 9.35 5,550 8.44 296 5 475

Clear Creek 7/22/2004 14.00 0.27 23.8 6.27 1,988 8.14 270 13 221

Crazy Woman Creek 7/22/2004 4.85 0.26 25.0 10.00 2,981 8.35 320 7 1,216

Tongue R at Miles City 7/25/2004 19.10 0.26 26.3 10.70 1,210 8.48 262 12 262

Tongue R at Brandenburg 7/25/2004 25.90 0.83 20.4 7.44 766 8.50 200 12 171

Tongue R nr Birney 7/23/2004 19.10 0.34 20.9 7.92 575 8.49 206 8 206

Hanging Woman Creek 7/23/2004 2.98 0.09 17.9 6.50 2,879 8.68 660 5 256

Tongue R blw dam 7/19/2004 ---- ---- ---- ---- ---- ---- ---- 8 22

Tongue R at Stateline 7/19/2004 35.30 0.72 23.8 6.04 647 8.46 204 12 74

Prairie Dog Creek 7/21/2004 5.10 0.42 18.5 7.94 1,518 8.38 326 4 28

Goose Creek 7/20/2004 15.40 0.43 23.8 11.5, 724 8.80 252 8 80

Tongue R at Monarch 7/20/2004 21.00 0.44 26.2 9.95 355 8.77 168 7 90

the Powder and Tongue Rivers. We plan 

to conduct on-site toxicity experiments to 

assess the survival of fish under natural 

conditions, though such experiments lack 

the control provided in the laboratory. 

In addition to providing data about 

effects of sodium bicarbonate on survival 

and growth of fish, toxicity studies can 

provide information about the health of 

fish that may survive the exposure, or 

“sub-lethal” effects of sodium bicarbonate. We collected samples during the 

chronic experiments to define some sublethal effects of sodium bicarbonate and 

to help explain how sodium bicarbonate 

might work to deteriorate the health of 

fish. Future plans include measuring and 

interpreting analyses of histology, Na/K 

ATPase activity, and whole body ion 

content in samples collected to date.

4

For Information

Don Skaar, Montana Fish, Wildlife and 

Parks; 406-444-5686; dskaar@mt.gov

Aïda Farag, U.S. Geological Survey; 

307-733-2314, extension 11; 

aida_farag@usgs.gov

David Harper, U.S. Geological Survey; 

307-733-2314, extension 14; 

david_harper@usgs.gov