U.S. Department of the Interior

U.S. Geological Survey

Concentrations of Selected Trace Elements in 

Fish Tissue and Streambed Sediment in the C

Fork-Pend Oreille and Spokane River Basins

Washington, Idaho, and Montana, 1998

Water-Resources Investigations Report 00–4159

Oreille

Spokane

Coeur

d' Alene

Coeur

Coeur

d' Alene

Lake

Pend

Oreille

Lake

Spokane

Missoula

Kalispell

Flathead

Flathead

Lake

Clark

Fork

Clark

Blackfoot

B

Bitterroot River

Fork

River

d' Alene

River

River

Riv

Pend

Kellogg

River

Priest

Lake

National Water-Quality 

Assessment Program

U.S. Department of the Interior

U.S. Geological Survey

Concentrations of Selected Trace Elements in 

Fish Tissue and Streambed Sediment in the 

Clark Fork-Pend Oreille and Spokane River 

Basins, Washington, Idaho, and Montana, 199

By T.R. Maret and K.D. Skinner

Water-Resources Investigations Report 00–4159

National Water-Quality Assessment Program

Boise, Idaho

2000
Con

U.S. DEPARTMENT OF THE INTERIOR

BRUCE BABBITT, Secretary

U.S. GEOLOGICAL SURVEY

Charles G. Groat, Director

Any use of firm, trade, and brand names in this report is for

identification purposes only and does not constitute 

endorsement by the U.S. Government.

Additional information can be obtained from: Copies of this report can be purchased from

District Chief U.S. Geological Survey

U.S. Geological Survey Information Services

230 Collins Road Box 25286

Boise, ID 83702-4520 Federal Center

http://idaho.usgs.gov Denver, CO 80225

e-mail: infoservices@usgs.gov

Information regarding the National Water-Quality Assessment (NAWQA) Program is available on 

Internet via the World Wide Web. You may connect to the NAWQA Home Pages using the Unive

Resource Locator (URL) at:

http://wwwrvares.er.usgs.gov/nawqa/nawqa_home.html

or

http://montana.usgs.gov/nrok/nrokpage.html
The mission of the U.S. Geological Survey 

(USGS) is to assess the quantity and quality of the 

earth resources of the Nation and to provide information that will assist resource managers and policymakers at Federal, State, and local levels in making sound 

decisions. Assessment of water-quality conditions and 

trends is an important part of this overall mission. 

One of the greatest challenges faced by waterresources scientists is acquiring reliable information 

that will guide the use and protection of the Nation’s 

water resources. That challenge is being addressed by 

Federal, State, interstate, and local water-resource 

agencies and by many academic institutions. These 

organizations are collecting water-quality data for a 

host of purposes that include: compliance with permits 

and water-supply standards; development of remediation plans for a specific contamination problem; operational decisions on industrial, wastewater, or watersupply facilities; and research on factors that affect 

water quality. An additional need for water-quality 

information is to provide a basis on which regionaland national-level policy decisions can be based. Wise 

decisions must be based on sound information. As a 

society we need to know whether certain types of 

water-quality problems are isolated or ubiquitous, 

whether there are significant differences in conditions 

among regions, whether the conditions are changing 

over time, and why these conditions change from place 

to place and over time. The information can be used to 

help determine the efficacy of existing water-quality 

policies and to help analysts determine the need for and 

likely consequence of new policies.

To address these needs, the Congress appropriated 

funds in 1986 for the USGS to begin a pilot program in 

seven project areas to develop and refine the National 

Water-Quality Assessment (NAWQA) Program. In 

1991, the USGS began full implementation of the program. The NAWQA Program builds upon an existing 

base of water-quality studies of the USGS, as well as 

those of other Federal, State, and local agencies. The 

objectives of the NAWQA Program are to:

•Describe current water-quality conditions 

large part of the Nation’s freshwater streams, ri

and aquifers.

•Describe how water quality is changing ov

•Improve understanding of the primary natu

human factors that affect water-quality conditio

This information will help support the deve

ment and evaluation of management, regulatory

monitoring decisions by other Federal, State, an

agencies to protect, use, and enhance water reso

The goals of the NAWQA Program are bein

achieved through ongoing and proposed investi

of 59 of the Nation’s most important river basin

aquifer systems, which are referred to as study 

These study units are distributed throughout the 

and cover a diversity of hydrogeologic settings. 

than two-thirds of the Nation’s freshwater use o

within the 59 study units and more than two-thi

the people served by public water-supply system

within their boundaries.

National synthesis of data analysis, based o

aggregation of comparable information obtaine

the study units, is a major component of the pro

This effort focuses on selected water-quality top

using nationally consistent information. Compa

studies will explain differences and similarities 

observed water-quality conditions among study 

and will identify changes and trends and their c

The first topics addressed by the national synth

pesticides, nutrients, volatile organic compound

aquatic biology. Discussions on these and other 

quality topics will be published in periodic sum

of the quality of the Nation’s ground and surfac

as the information becomes available.

This report is an element of the comprehen

body of information developed as part of the NA

Program. The program depends heavily on the 

cooperation, and information from many Feder

State, interstate, Tribal, and local agencies and t

lic. The assistance and suggestions of all are gre

appreciated.

Robert M. Hir

Chief Hydrolo

Fore

FOREWORD

Con

CONTENTS

Foreword ...........................................................................................................................................................................

Abstract ............................................................................................................................................................................

Introduction .......................................................................................................................................................................

Purpose and scope ...................................................................................................................................................

Acknowledgments ..................................................................................................................................................

Description of study area...................................................................................................................................................

Materials and methods ......................................................................................................................................................

Sample collection, preparation, and analysis ..........................................................................................................

Quality-control procedures......................................................................................................................................

Data analysis ...........................................................................................................................................................

Trace-element occurrence and relative concentrations .....................................................................................................

Trace-element concentrations in bed sediment and fish tissue ...............................................................................

Trace-element concentrations reported in other studies and guidelines..................................................................

Relations among trace-element concentrations, land use, and geology............................................................................

Summary ...........................................................................................................................................................................

References cited ................................................................................................................................................................

Appendix A. Hard-rock mining activities in the Northern Rockies Intermontane Basins study area and within a 

250-meter buffer area along perennial streams in each subbasin ..............................................................................

Appendix B. Species, sizes, and tissue types of fish collected in the Northern Rockies Intermontane Basins study 

area, 1998 ...................................................................................................................................................................

FIGURES

1. Map showing sampling site locations, production mines, and significant mineral deposits, Northern 

Rockies Intermontane Basins study area ............................................................................................................

2. Graph showing densities of significant deposits in the 250-meter stream buffer and production mines 

upstream from each sampling site, Northern Rockies Intermontane Basins study area.....................................

3. Graphs showing trace-element concentrations in bed sediment and fish tissue (livers and fillets) at all 

sampling sites in the Northern Rockies Intermontane Basins study area ..........................................................

4. Boxplots showing distribution of ratios of trace-element concentrations in fish tissue (livers and fillets) to 

concentrations in bed sediment, Northern Rockies Intermontane Basins study area .........................................

5. Graph showing relations between production mine density and sum of trace-element concentrations in bed

sediment, Northern Rockies Intermontane Basins study area ............................................................................

TABLES

1. Sampling sites and selected site and subbasin characteristics, Northern Rockies Intermontane Basins study 

area, 1998............................................................................................................................................................

2. Minimum reporting levels and trace-element concentrations in bed sediment and fish tissue, Northern 

Rockies Intermontane Basins study area ............................................................................................................

3. Comparison among various trace-element guidelines and concentrations detected in bed sediment and fish 

tissue, Northern Rockies Intermontane Basins study area..................................................................................

4. Spearman’s correlation coefficients for production mine densities, significant deposit densities, and traceelement concentrations in fish tissue (livers and fillets) and bed sediment, Northern Rockies Intermontane

Basins study area.................................................................................................................................................
0 Trace Elements in Fish Tissue and Sediment, Clark Fork-Pend Oreille and Spokane River Basins, 1998

CONVERSION FACTORS AND OTHER ABBREVIATED UNITS

Multiply By To obtain

centimeter (cm) 0.3937 inch

gram (g) 0.03527 ounce, avoirdupois

hectare (ha) 2.471 acre

kilogram (kg) 2.205 pound, avoirdupois

kilometer (km) 0.6214 mile

meter (m) 3.281 foot

metric ton 1.102 ton, short (2,000 pounds)

millimeter (mm) 0.03937 inch

square kilometer (km2) 0.3861 square mile

Temperature in degrees Celsius (°C) can be converted to degrees Fahrenheit (°F) as follows:

°F=(1.8) (°C)+32

Other abbreviated units:

μg/g microgram per gram 

μg/L microgram per liter

vi
Introd

ABSTRACT

Fish tissue and bed sediment samples were 

collected from 16 stream sites in the Northern 

Rockies Intermontane Basins study area in 1998 as 

part of the U.S. Geological Survey National WaterQuality Assessment Program. Bed sediment samples were analyzed for 45 trace elements, and fish 

livers and sportfish fillets were analyzed for 22 

elements to characterize the occurrence and distribution of these elements in relation to stream characteristics and land use activities. Nine trace elements of environmental concern—arsenic, cadmium, chromium, copper, lead, mercury, nickel, 

selenium, and zinc—were detected in bed sediment, but not all of these elements were detected 

in fish tissue. Trace-element concentrations were 

highest in bed sediment samples collected at sites 

downstream from significant natural mineral 

deposits and (or) mining activities. Arsenic, cadmium, copper, lead, mercury, and zinc in bed sediment at some sites were elevated relative to 

national median concentrations, and some concentrations were at levels that can adversely affect 

aquatic biota. Although trace-element concentrations in bed sediment exceeded various guidelines, 

no concentrations in sportfish fillets exceeded U.S. 

Environmental Protection Agency screening values for the protection of human health. Correlations between most trace-element concentrations 

in bed sediment and fish tissue (liver and fillet) 

were not significant (r<±0.50, p>0.05). Concentrations of arsenic, cadmium, copper, lead, mercury, 

nickel, selenium, and zinc in bed sediment were 

significantly correlated (r=0.53 to 0.88, p<0

with natural mineral deposits and mining ac

ties, but concentrations in fish tissue genera

were not correlated with these measures. Re

sion analysis between mine density and the 

trace-element concentrations in bed sedime

identified two statistically significant relatio

(r2=0.95 and 0.99, p<0.001) that correspond

trace-element enrichment categories. These 

relations warrant further study using mine d

as an explanatory variable to predict trace-e

concentrations in bed sediment.

INTRODUCTION

Introduction

The U.S. Geological Survey (USGS) Natio

Water-Quality Assessment (NAWQA) Program 

perennial program designed to produce a comp

sive assessment of the quality of the Nation’s st

and aquifer resources (Hirsch and others, 1988; 

and others, 1990). Investigations in more than 5

NAWQA study units use an integrated approach 

assess the status and trends of water quality in m

river basins of the Nation (Gurtz, 1994). This a

ment consists of the collection of chemical, phy

and biological data at sites representing a wide r

water-quality conditions. One component of thi

grated assessment of water quality is examinati

the occurrence and distribution of trace elemen

biological tissue and bed sediments on a basinw

scale. 

This report presents results of trace-elemen

ses of fish tissue and associated bed sediments c

lected in 1998 in the Northern Rockies Intermo

Basins (NROK) study area. Data were collected 

representing a gradient of stream sizes, areas of 

mineral deposits, and areas affected by mining 

Concentrations of Selected Trace Elements in 

Fish Tissue and Streambed Sediment in the 

Clark Fork-Pend Oreille and Spokane River 

Basins, Washington, Idaho, and Montana, 199

By T.R. Maret and K.D. Skinner
2 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

0 2

0

4

4

6 MILES

2 6 KILOMETERS

10

12

11

Coeur

River

d' Alene

South

Fork

Kellogg

North

Fork

116° 15' 116° 116° 45'

47° 37' 30"

47° 30'

IDAHO

WASHINGTON MONTANA

Study

area

Figure 1. Sampling site locations, production mines, and significant mineral deposits, Northern Rockies Intermontan

Base from U.S. Geological Survey digital data,

Hydrologic unit maps, 1:100,000, 1994;

Rivers and Streams, 1:250,000, 1994;

Albers Equal-Area projection

Standard parallels 46° 00', 48° 30',

and -115° 00', 45° 00'

No false easting or false northing

117°

117°

118°

118°

116°

116°

49°

48°

47°

Pend

Oreille

River

Spokane

Kellogg

Coeur

d'Alene

Pend

Oreille

Lake

Spokane 

River

Priest

Priest

Lake

River

South Fork

North

Fork

Coeur

River

 Coeur

 d'Alene

 Lake

d'Alene

Clark

14

11

12

15 10

16

9
Introd

Basins study area.

0

0

10

10

30

30

20

20

40

40

50 MILES

50 KILOMETERS

115°

115°

114°

114°

113°

46° 46°

47°

48°

49°

113°

Missoula

Kalispell

Flathead

Lake

Clark

Clark

Blackfoot

Butte

Bitterroot

River

Fork

River

River

Flathead

Fork

7

1

3

2

5

4

6 8

Sampling site and number—

 refers to table 1

Production mine—Active and 

 past

Significant mineral deposit

 Active

 Past

 Undeveloped

EXPLANATION

9
4 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

ties. Results are summarized for nine elements that are 

of environmental concern—arsenic, cadmium, chromium, copper, lead, mercury, nickel, selenium, and 

zinc (hereafter abbreviated As, Cd, Cr, Cu, Pb, Hg, Ni, 

Se, and Zn, respectively). All nine elements are on the 

U.S. Environmental Protection Agency’s (USEPA) list 

of 126 Priority Pollutants (U.S. Environmental Protection Agency, 1994).

Trace elements in the aquatic environment occur 

naturally from weathering of rocks and mineral soils 

and from human sources such as the burning of fossil 

fuels, industrial discharges, automobile emissions, 

mining, and agricultural pesticides and fertilizers. Historical and current mining practices are believed to 

affect the quality of streams and aquifers in the NROK 

study area (fig. 1) (Hornberger and others, 1997; 

Tornes, 1997; Beckwith, 1998). Past mining activities 

have resulted in Superfund investigations and remediations along the upper Clark Fork and South Fork Coeur 

d’Alene River. The two largest Superfund sites in the 

Nation are located in the study area—the Anaconda 

Company Smelter near Butte, Montana, and the Bunker Hill Smelter near Kellogg, Idaho (Doppelt and others, 1993). In addition, the U.S. Department of the Interior is currently conducting Natural Resource Damage 

Assessments in and around these Superfund complexes 

(Beckwith, 1998). 

Many trace elements, especially Cu, Se, and Zn, 

are essential to animal and plant nutrition but can be 

toxic in high concentrations (U.S. Department of the 

Interior, 1998). As, Cd, Cu, Pb, Hg, Se, and Zn are 

some of the more notable elements found to be toxic to 

aquatic life (Eisler, 1985, 1987, 1988; U.S. Department 

of the Interior, 1998). Aquatic organisms have developed mechanisms to regulate internal concentrations of 

certain trace elements in tissues or to mitigate their toxicity (Law, 1996). However, because of the slow rate of 

elimination, some of the more toxic trace elements, 

such as Hg, Cd, Se, and Pb, tend to bioaccumulate, and 

Hg may biomagnify in aquatic food chains (Eisler, 

1985, 1988; Wiener and Spry, 1996; U.S. Department 

of the Interior, 1998). As a result, trace-element concentrations in tissues of aquatic species generally 

increase with increasing age, body size, and trophic 

status (Wiener and Spry, 1996; Park and Curtis, 1997).

Trace-element concentrations are generally higher 

in bed sediments and tissue than in water (Rainbow, 

1996). Trace-element concentrations in sediment can 

be at least three orders of magnitude greater than the 

same elements in aqueous phases because trace elements often sorb to particle surfaces (Horowitz

Elevated trace-element concentrations in fine-g

bed sediment and tissue of fish in streams near 

activities in Colorado have been documented (H

and Tate, 1997; Deacon and Driver, 1999). 

Concentrations of contaminants in tissue pr

time-integrated assessment of contaminants and 

ter understanding of the complexities of the fate

bution, and effects of various contaminants (Cr

and Luoma, 1993). Trace elements can be inges

with streambed sediment or suspended sedimen

water column by benthic organisms and can acc

late and move through the food chain. Fish are 

larly good indicators of biologically available c

nants because environmental contaminants can 

mulate in their bodies at higher concentrations t

surrounding water. Many trace elements concen

the viscera of fish such as the liver and kidneys 

ford and Luoma, 1993). Notable exceptions inc

Hg, which tends to concentrate to higher levels 

cle (Goldstein and others, 1996), and Pb, which 

entially sequesters in active calcification areas s

scales, fin rays, vertebrae, and opercula (Sorens

1991). The concentrations of trace elements in 

and muscle also may vary, depending on a num

factors such as the chemical properties of the el

and the species of fish. 

A summary of tissue contaminant informat

Maret and Dutton (1999) indicated that concent

of Cd, Cu, Pb, Hg, and Zn in fish and macroinv

brates collected in and around mining sites in th

area typically were elevated, compared with ba

ground concentrations. Some concentrations in 

exceeded State and Federal guidelines for prote

human health and (or) wildlife. Maret and Dutt

concluded there was a need for further study to 

terize the severity of contamination in fish tissu

1998, no fish consumption advisories or fishing 

tions on any rivers within the study area had be

issued as a result of elevated trace elements. Th

due in part to the lack of sportfish tissue data co

for the assessment of human health risk (Maret 

Dutton, 1999). According to the Natural Resour

Defense Council (1998), fish tissue contaminan

serious national health concern that has not bee

quately addressed by current pollution abateme

monitoring programs.
Description of Study 

Purpose and Scope

The purpose of this report is to summarize the concentrations and distribution of selected trace elements 

in fish tissue and bed sediment in the NROK study area 

and provide information to determine whether concentrations are at levels of concern to human health and 

aquatic life. Relations among trace-element concentrations in fish tissue and bed sediment and basinwide 

land use, geology, and mining activities also are evaluated. The findings of this report will provide a better 

understanding of trace-element concentrations in 

aquatic environments that are highly enriched with 

trace elements. 

Acknowledgments

Numerous individuals from the USGS assisted in 

collecting and processing data during the course of the 

study—John Baker, Dorothy Barnett, Mike Beckwith, 

Craig Bowers, DeAnn Dutton, Kari Finley, Steve 

Goodbred, Keith Hein, Ivan James, Doug Ott, Terry 

Short, and Lan Tornes. Colleague reviews by Rod 

Deweese, Terry Short, and Lan Tornes improved the 

quality of the manuscript.

DESCRIPTION OF STUDY AREA

Description of Study Area

The NROK study area (fig. 1) is an 81,585-km2

area in western Montana, northern Idaho, and northeastern Washington. The study area is composed of two 

major river basins: the Clark Fork-Pend Oreille River 

Basin, which encompasses about 64,491 km2, and the 

Spokane River Basin, which encompasses about 

17,094 km2 (Maret and Dutton, 1999). 

The study area includes four ecoregions: Northern 

Rockies (72 percent); Montana Valley and Foothill 

Prairies (16 percent); Canadian Rockies (9 percent); 

and Columbia Plateau (3 percent) (Maret and Dutton, 

1999). The Northern Rockies and Canadian Rockies 

ecoregions characterize the high-elevation, mountainous parts of the study area. These ecoregions consist 

primarily of coniferous forests, and the predominant 

land uses are timber, mining, and recreation. The Montana Valley and Foothill Prairies and Columbia Plateau 

ecoregions represent lower elevations characterized by 

flatlands and rolling hills vegetated with grasses and, in 

drier areas, sagebrush. Land use in these lower elevation ecoregions is primarily dryland and irrigate

land and grazing. 

The population of the study area in 1990 wa

725,000: 350,000 in Washington; 255,000 in M

and 120,000 in Idaho (Tornes, 1997). Land own

is about 56 percent public, 37 percent private, a

percent Tribal.

The study area has a complex geologic hist

sedimentation, compressional deformation, ign

activity, and, most recently, extensional block f

(Kendy and Tresch, 1996). Because of the exten

mineralized areas in the NROK, natural conditi

affect trace-element concentrations in streams. 

summarizes the major geologic formations in th

area.

Streams in the study area are predominantly 

water, and snowmelt runoff during April to July 

sents the main source of surface water and grou

water (Kendy and Tresch, 1996). Upland forest 

lower elevation rangeland streams typically hav

coarse-grained substrates (gravel and cobble), h

dients (greater than 1.0 percent), well-defined r

pool habitats, and sparse macrophyte growth. L

rivers and streams at lower elevations typically 

finer grained substrates and lower gradients. 

The quality of surface and ground water in b

Spokane River and Clark Fork-Pend Oreille Bas

been adversely affected by mining activities. At 

1,350 active and abandoned hard-rock mines of 

sizes are located in the study area (fig. 1, appen

Historically, metal extraction and processing w

tively inefficient, yielding large volumes of met

tailings that were deposited to nearby streams. M

these mines were located near streams (see fig. 

enlargement of the South Fork Coeur d’Alene R

Basin). Mine tailings in the study area typically 

elevated levels of the trace elements As, Cd, Cu

Hg, and Zn. These tailings and mines continue 

vide a source of trace elements to streams, lake

reservoirs as streams meander through and erod

ings deposits and transport them downstream. M

tailings entering the South Fork Coeur d’Alene 

have been transported and deposited along the r

channel and flood plain into Coeur d’Alene Lak

out of the lake into the Spokane River. Horowit

others (1995) estimated that 85 percent of the C

d’Alene Lake bed is enriched with trace elemen

USEPA (1997) National Sediment Inventory id

the Coeur d’Alene River and Lake as “areas of 
6 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998 Table 1. Sampling sites and selected site and subbasin characteristics, Northern Rockies Intermontane Basins study area, 1998 [No., number; fig., figure; km2, square kilometers; m, meters; MT, Montana; ID, Idaho; WA, Washington; F, forest land; R, rangeland; A, agricultural land; U, urban and (or) residential land; OLU, other, including barren rock, tundra, water, or transitional; IR, intrusive rock; ER, extrusive rock; AD, alluvial deposits; SD, sedimentary rock; MR, metasedimentary rock, undifferen- tiated; GD, glacial deposits; MTR, metamorphic rock; CC, carbonate and clastic rock; OGT, other, includes lakes and undifferentiated deposits] Site Basin No. area Elevation Sampling site name (fig. 1) (km2) (m) Percent land use Percent geologic type1 Clark Fork near Galen, MT. . . . . . . . . . . . . . . . . . . . . . . 1 1,729 1,447 F 44, R 43, A 2, U 3, OLU 8 IR 32, ER 22, CC 12, AD 11, SD 10, OGT 2 Rock Creek near Clinton, MT. . . . . . . . . . . . . . . . . . . . . 2 2,314 1,073 F 81, R 16, OLU 3 MR 68, IR 13, SD 6, GD 6, CC 3, ER 2, AD 2 Clark Fork at Turah Bridge near Bonner, MT. . . . . . . . . 3 9,520 1,012 F 58, R 32, A 6, OLU 4 MR 29, CC 18, IR 14, ER 14, SD 13, AD 8, GD 3, OGT 1 Blackfoot River near Helmville, MT . . . . . . . . . . . . . . . 4 1,242 1,311 F 89, R 5, A 3, OLU 3 MR 66, GD 13, ER 10, AD 8, CC 1, OGT 2 Bitterroot River near Missoula, MT . . . . . . . . . . . . . . . . 5 7,250 948 F 72, R 13, A 9, OLU 6 IR 48, MR 27, MTR 9, AD 6, SD 3, OGT 7 Clark Fork at St. Regis, MT . . . . . . . . . . . . . . . . . . . . . . 6 27,819 806 F 72, R 18, A 6, OLU 4 MR 45, IR 18, AD 7, ER 7, SD 7, GD 5, CC 7, MTR 2, OGT 2 Middle Fork Flathead River near West Glacier, MT. . . . 7 2,939 954 F 71, R 15, OLU 14 MR 69, CC 17, GD 10, AD 3, OGT 1 Flathead River at Perma, MT2. . . . . . . . . . . . . . . . . . . . . 8 21,787 753 F 70, R 13, A 8, OLU 9 MR 64, GD 23, CC 6, AD 4, OGT 3 Priest River near Priest River, ID . . . . . . . . . . . . . . . . . . 9 2,460 637 F 93, R 2, OLU 5 IR 44, MR 24, AD 15, MTR 8, GD 4, OGT 5 North Fork Coeur d’Alene River at Enaville, ID . . . . . . 10 2,325 640 F 98, R 2 MR 100 South Fork Coeur d’Alene River near Mullan, ID . . . . . 11 18 1,100 F 97, OLU 3 MR 100 South Fork Coeur d’Alene River near Pinehurst, ID . . . 12 738 668 F 88, R 6, OLU 6 MR 97, IR 1, OGT 2 St. Joe River at Red Ives Ranger Station, ID . . . . . . . . . 13 275 1,128 F 91, R 8, OLU 1 MR 100 St. Joe River at Calder, ID. . . . . . . . . . . . . . . . . . . . . . . . 14 2,679 662 F 93, R 7 MR 79, MTR 17, IR 4 Hangman Creek at Spokane, WA . . . . . . . . . . . . . . . . . . 15 1,785 523 F 33, A 63, OLU 4 ER 48, MR 44, MTR 5, AD 2, IR 1 Spokane River above 7 Mile Bridge near 

 Spokane, WA. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 12,995 494 F 78, R 3, A 14, U 3, OLU 2 MR 65, ER 13, MTR 12, AD 6, IR 2, OGT 2

1Geologic types taken from Tuck and others (1996).2Includes portion of the basin in Canada.
Materials and Me

ble concern for sediment contamination,” the most 

severe contamination category in their assessment.

Andrews (1987) estimated that 91 million metric 

tons of tailings have been supplied to the headwaters of 

the Clark Fork during the period of mining from 1880 

to 1982. Metal enrichment remains evident in the Clark 

Fork sediments and biota for more than 280 km, from 

Butte to near Missoula, Mont. (Moore and Luoma, 

1990). Elevated trace-element concentrations in the 

Clark Fork in Montana have caused fish kills and suppression of fish production (Phillips and Lipton, 1995). 

Juvenile trout also have shown reduced growth and survival as a result of ingesting macroinvertebrates from 

the Clark Fork, where trace-element concentrations are 

elevated (Farag and others, 1994; Woodward and others, 1994). Contrary to this, the USEPA’s recent 

(1999) Ecological Risk Assessment has determined 

that these feeding studies are inconclusive and recommend further studies to evaluate trout growth and survival in the Clark Fork (D.S. Brown, U.S. Environmental Protection Agency, written commun., 2000).

MATERIALS AND METHODS

Materials and Methods

Sample Collection, Preparation, and 

Analysis

Trace elements in bottom sediment and fish tissue 

were sampled from 16 sites throughout the study area 

(table 1, fig. 1) at low-flow conditions during June to 

September 1998. Bed sediment and fish tissue were 

collected from the same 300- to 1,000-m reach at each 

site. Samples were collected in accordance with USGS 

NAWQA procedures (Meador and others, 1993; Shelton and Capel, 1994). Trace elements in tissue were 

analyzed by the USGS National Water Quality Laboratory in Arvada, Colo. (Hoffman, 1996). Trace elements 

in bed sediment were analyzed by the USGS Mineral 

Resources Laboratory in Lakewood, Colo. (Arbogast, 

1990; Briggs and Meier, 1999). 

The upper 2 cm of bed sediment was collected 

from undisturbed, continuously wetted, depositional 

zones by using a plastic scoop. Five to 10 subsamples 

of streambed sediment within the sampling reach were 

composited and sieved onsite at the <63-micron size 

fraction and submitted to the laboratory for analysis 

(Shelton and Capel, 1994). Because trace elements are 

not expected to significantly sorb to the >63-micron 

sediment particles, the smaller size fraction was chosen 

to normalize the size fraction and to maximize the concentration of trace elements. Because the <63-m

size fraction, rather than bulk sediment, was an

the likelihood of exceeding a guideline or scree

value (SV) based on bulk sediment concentratio

be increased. A bed sediment sample also was co

and sieved to retain the <2-mm particle for parti

analysis by the USGS laboratory in Vancouver, 

Fish were collected using electrofishing tech

from all habitats within a reach (Meador and ot

1993). Four to 17 adult fish of the same species 

similar sizes were collected at each site. At mos

livers and fillets were removed from different in

als of the same species and combined for a sing

posite sample. At a few sites, both liver and fille

ples were collected from the same individuals o

low numbers of adult fish of similar size at thos

Species collected included brook trout (Salvelin

tinalis), brown trout (Salmo trutta), cutthroat tr

(Oncorhynchus clarki), largescale sucker (Cato

macrocheilus), mountain whitefish (Prosopium 

iamsoni), and rainbow trout (Oncorhynchus my

Summary statistics about the fish sampled are p

in appendix B. Fish were identified, measured, 

ined for external anomalies, and processed indo

mobile laboratory to avoid contamination. Fish 

lected at all sites appeared in generally good hea

external anomalies were seldom observed. Com

samples of livers and fillets were obtained from 

collected at each site. Livers from each species 

placed in plastic containers; fillets from sportfis

obtained by removing a fillet from one side of th

and removing the skin (U.S. Environmental Pro

Agency, 1995). All samples were frozen onsite 

dry ice. Further details on tissue sampling meth

preparation used in this study are included in a 

by Crawford and Luoma (1993).

Fish tissue samples were prepared for trace

ment analyses using a nitric acid digestion at 70

lowed by the addition of hydrogen peroxide to 

pose biological material. The bed sediment sam

were digested using a mixture of hydrochloric, 

perchloric, and hydrofluoric acids. The resultan

tions from tissue and bed sediment were evapor

incipient dryness, reconstituted with 5 percent n

acid, and filtered. Fish tissue extracts were analy

methods outlined in a report by Hoffman (1996

included inductively coupled plasma-atomic em

spectrometry and inductively coupled plasma-m

spectrometry; Hg was analyzed by cold vapor-a

adsorption spectrometry. Bed sediments were an
8 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

for most trace elements by using inductively coupled 

plasma-mass spectrometry (Briggs and Meier, 1999); 

Se was analyzed by continuous hydride generationatomic adsorption spectrometry and Hg by cold vaporatomic adsorption spectrometry (Arbogast, 1990). 

Quality-Control Procedures

Field replicate samples were collected at three sites 

to determine environmental and sampling technique 

variability for bed sediment and (or) fish tissue. Triplicate samples of bed sediment to assess within-site variability were collected at sites 3 and 12. Triplicate samples of livers were collected at site 3, and duplicate 

samples of fillets were collected at site 7 (appendix B). 

Relative percent differences in trace-element concentrations among replicate sediment samples were greater 

than differences among replicate tissue samples. The 

differences among bed sediment replicates ranged from 

about 9 percent at site 3 to 107 percent at site 12. Differences were greatest at site 12 for Cd (107 percent), 

Pb (71 percent), and Zn (103 percent). The coefficients 

of variation among all elements detected in replicates 

of bed sediment ranged from 3 to 55 percent. Differences among triplicate liver samples at site 3 ranged 

from about 18 to 75 percent. The coefficients of variation among all elements detected in liver replicates 

ranged from 10 to 38 percent. Differences between 

duplicate fillet samples from the same fish at site 7 

ranged from about 8 to 38 percent. Contrary to these 

findings, Bonn (1999) observed a greater difference in 

concentrations, ranging from 20 to 200 percent for similar elements, among replicate tissue samples than 

among bed sediment samples. 

The large variability in concentrations among bed 

sediment field replicates may be due to where samples 

were collected. Replicates collected at mining-affected 

reaches (sites 3 and 12) exhibited higher concentrations 

of some trace elements relative to concentrations in 

samples from most other sites. Streams affected by 

mine-tailings deposits can exhibit variable mineral 

deposits along streambanks that reflect past mining 

practices and subsequent instream deposition. These 

replicate samples represent both spatial variability and 

the variability associated with collection and analysis 

of separate samples.

Laboratory quality control for bed sediment samples included analyses of a reference material (enriched 

soil) and an analytical replicate for each batch of samples analyzed. Values for elements in reference 

rial were within quality-assurance guidelines of 

standard deviations (Arbogast, 1990).

Laboratory quality control for fish tissue in

analyses of blank samples, duplicate samples, a

standard reference materials (National Institute 

Standards and Technology oyster tissue and bov

liver) for each batch of tissue samples. The NW

reported values were within ±3 standard deviati

the reference material certified values (Arbogas

1990). 

Data Analysis

Forty-five and 22 trace elements were analy

bed sediment and fish tissue, respectively. A co

list of all elements and their concentrations can 

found in the USGS National Water Information 

data base. Nine of these elements that are of env

mental concern—As, Cd, Cr, Cu, Pb, Hg, Ni, S

Zn—were selected for discussion. 

Matrices of bivariate correlations were cons

using SYSTAT (Wilkinson, 1998) to examine a

ble combinations of responses and explanatory 

ables. Mean concentrations were used in the da

ysis for replicate samples. Nondetections (below 

minimum reporting level) were set to zero prior 

analysis. 

Trace-element concentrations in bed sedim

were not normalized to organic carbon because 

nificant correlations (p<0.05) were found betwe

centrations and percent organic carbon. Particle

analysis prior to sieving determined that the bed 

ment samples were composed predominantly o

the <63-micron particle-size fraction ranged fro

40 percent for all samples. Organic carbon range

0.7 to 4.9 percent for all bed sediment samples.

Spearman’s rho was used as a measure of th

degree of association between trace-element co

tions and landscape variables that included land 

geology, and mining activity. This statistic also 

used to evaluate relations between concentratio

sediment and tissue samples. A Mann-Whitney t

used to test differences in median concentration

liver and fillet samples. 

Landscape variables upstream from each si

determined using a geographic information syst

(ArcView). Spatial coverages were obtained fro

Interior Columbia Basin Ecosystem Manageme
Trace-Element Occurrence and Relative Concentr

Project World Wide Web site (U.S. Forest Service and 

Bureau of Land Management, 1998).

 Land use was modified from 1:250,000-scale digital data (U.S. Geological Survey, 1986) consisting of a 

level-II classification scheme at a 16-ha mapping resolution (Anderson and others, 1976). Geologic information was obtained from a report by Tuck and others 

(1996). Trace-element enrichment measures were 

determined for each basin to provide indicators of significant natural mineral deposits and human disturbance from mining. Production mines for each basin 

were located using the U.S. Bureau of Mines (1995) 

Minerals Availability System. Significant deposits are 

defined by Long and others (1998) as large, natural 

source areas that, prior to being mined, contained at 

least one of the following: 50,000 metric tons of copper, 2 metric tons of gold, 30,000 metric tons of lead, 

85 metric tons of silver, or 50,000 metric tons of zinc. 

There are 66 significant deposits in the study area, and 

Long and others reported that these deposits accounted 

for more than 90 percent of past mine production of 

these elements. These deposits can be grouped into 

three mining categories—active (8 deposits), past (49 

deposits), and undeveloped (9 deposits). Densities of 

mine category groups were determined for a 250-m 

buffer area along each stream margin for all stream 

channels in each basin. Figure 2 summarizes the sample sites in relation to significant mineral deposits and 

production mines upstream from each site. Sites are 

grouped along the x-axis on the basis of whether they 

have significant deposits. Sites 1, 3, 4, 6, 10, 12, and 16 

are considered to be enriched with trace elements from 

these natural and human-caused sources relative to the 

other sample sites, whereas sites 2, 5, 7, 8, 9, 11, 13, 

14, and 15 are unenriched with trace elements.

Analyses of bed sediment and liver tissue of fish 

collected from streams across the Nation during 1992–

96 for the NAWQA Program were compared with analyses from this study (Rice, 1999; T. Short, U.S. Geological Survey, written commun., 1999). The USEPA 

SV (U.S. Environmental Protection Agency, 1995, 

1997) for selected trace elements was used to evaluate 

edible tissue (fillets) and bed sediment concentrations. 

The Canadian Interim Sediment Quality Guidelines 

(ISQGs) were used to evaluate the severity of the traceelement contamination in bed sediment (Canadian 

Council of Ministers of the Environment, 1995). 

Guidelines used in this report refer to any SV, action 

level, or elevated level (85th percentile, determined 

from the NAWQA Program) useful for assessin

taminant concentrations.

TRACE-ELEMENT OCCURRENCE AN

RELATIVE CONCENTRATIONS

Trace-Element Occurrence and Relative Concentrations

All nine trace elements were detected in all 

sediment samples; however, only the essential t

elements Cu, Se, and Zn were detected in all fis

samples. Hg, a nonessential trace element, was 

detected in 97 percent of the fish tissue samples

larly, the National Bioaccumulation Study detec

in 92 percent of the fish tissue samples collected 

rily in 1987 at more than 300 locations nationw

(U.S. Environmental Protection Agency, 1992). 

detected in only 45 percent of the fish tissue sam

The frequency of detection for the nonessential 

elements As, Cd, Hg, Ni, and Pb in tissue range

16 percent to 97 percent. 

Median concentrations of Cd, Cu, Se, and Z

significantly higher in liver than in fillet tissue (t

Further analysis of seven liver and fillet sample

the same fish of five different trout species (see 

dix B) resulted in similar significant differences 

median concentrations of these four trace eleme

Overall, median concentrations of Cu and Zn w

Trace-element

enriched

SIGNIFICANT DEPOSITS PER SQUARE

KILOMETER x 10-3

0.06

0.05

0.04

0.03

0.02

0.01

0

Figure 2. Densities of significant deposits in the 25

stream buffer and production mines upstream from e

pling site, Northern Rockies Intermontane Basins st

(Site names shown in table 1; locations shown in fig

2 7 5 8 4 10 9 11 1 3 6 13 14

SITE NUMBER

15

Production mines

Significant deposits

12 16
10 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

order of magnitude higher in livers than in fillets 

(table 2). 

Trace-element concentrations also can vary among 

species. Tissue of piscivorous species generally contains higher concentrations of Hg than does tissue of 

coexisting fish of lower trophic levels (Wiener and 

Spry, 1996). Hg concentrations in rainbow trout tissue 

have been found to be lower in muscle than in the liver 

and other organs, whereas concentrations in walleye 

(Stizostedion vitreum), carp (Cyprinus carpio), and 

largemouth bass (Micropterus salmoides) generally are 

highest in muscle tissue (Foster and others, 2000). It is 

apparent from these results that caution should be used 

when comparing tissue concentrations reported in other 

studies to those reported in this study, because results 

can vary depending on type of tissue and species 

analyzed.

Sites 1, 3, 4, 6, 10, 12, and 16 are considered 

enriched with trace elements relative to other sample 

sites on the basis of significant deposits (fig. 2, appendix A). Another characteristic of these enriched sites is 

that mining densities generally are higher than at sites 

with no significant deposits. 

Concentrations of As, Cd, Cu, Pb, Hg, and Zn in 

bed sediment were highest at these enriched sites, 

whereas concentrations of trace elements in fish tissue 

generally did not show this same pattern (fig. 3). A few 

exceptions included higher Cd concentrations in liver 

tissue and the detection of Pb in fillet tissue onl

enriched sites. 

The South Fork Coeur d’Alene River near P

hurst (site 12) contained the highest concentrati

Cd, Pb, Hg, and Zn in bed sediment. This site a

the highest concentrations of Cd, Pb, and Zn in 

sues. Some of these concentrations at this site ex

the national median by several orders of magnit

pilot study by Krabbenhoft and others (1999), w

consisted of 105 sampling sites nationwide, als

reported the highest concentrations of total Hg 

μg/g) in bed sediment at site 12. This concentra

similar to the range of Hg concentrations (4.5 to 

μg/g) in replicate samples collected at site 12 d

this study. Concentrations of Cu in bed sedimen

the upper Clark Fork (sites 1, 3, and 6) exceede

national median. According to a report by Phill

Lipton (1995), many of the past fish kills associ

with mining activities in the upper Clark Fork h

been caused primarily by Cu toxicity. 

 In the Clark Fork, concentrations of As, Cd

Pb, Se, and Zn in bed sediment decreased from 

downstream to site 6. This same decrease in con

tions of trace elements in bed sediment with dis

from mining sources on the Clark Fork was obs

by Andrews (1987). Deacon and Driver (1999) 

reported a decrease in trace-element concentrat

bed sediments of Colorado streams with distanc

mining source areas. This is the result of dilutio

Table 2. Minimum reporting levels and trace-element concentrations in bed sediment and fish tissue, Northern Rockie

Intermontane Basins study area

[Concentrations reported in micrograms per gram, dry weight; see appendix B for fish species analyzed; n, number of samples; <, less than]

Concentrations 

Tissue

 Bed sediment (n=16) Liver (n=16) Fillets (n=

Trace element sediment Tissue Median Range Median Range Median 

Arsenic . . . . . . . . . . . . 0.1 0.1 9.7 2.6–176 0.6 <0.1–1.5 0.2 <

Cadmium . . . . . . . . . . . .1 .1 .3 .1–51 11.8 <.1–10 1<.1 

Chromium . . . . . . . . . . 1 .05 43 35–65 .2 <.05–.6 .4 <

Copper . . . . . . . . . . . . . 1 .5 26 18–1,250 155 1.4–387 11.4 

Lead . . . . . . . . . . . . . . . 1 .1 42 12–6,600 .2 <.1–12 <.1 

Mercury . . . . . . . . . . . . .02 .1 .1 .2–5.5 .2 <.1–1.0 .2 

Nickel. . . . . . . . . . . . . . 2 .1 18 12–24 <.1 <.1–.3 <.1 

Selenium . . . . . . . . . . . .1 .1 .2 .1–.9 14.6 .4–24 11 

Zinc . . . . . . . . . . . . . . . 2 .5 98 46–6,133 1104 9.0–294 116 

1Medians significantly different (p<0.05) between fish liver and fillet tissue.

Bed

Minimum reporting

level
Trace-Element Occurrence and Relative Concentra

sediment from sources having lower concentrations of 

trace elements. Concentrations of Cr, Ni, and Se in bed 

sediments did not appear to be associated with traceelement-enriched sites. 

Results of this study indicate that concentrations of 

some trace elements in bed sediment and liver tissue of 

fish from NROK streams generally are higher than 

national median concentrations in sediment and fish 

tissue determined from the NAWQA Program, 1992–

96 (fig. 3). At one or more sites, As, Cd, Cr, Cu, Pb, Hg, 

Se, and Zn in bed sediment exceeded national median 

concentrations. The median concentrations of As, Pb, 

and Hg in bed sediment samples from all NROK sites 

(table 2) exceeded national median concentrations 

(fig. 3). Similarly, As, Cd, Cu, Pb, Hg, Se, and Zn in 

fish liver samples from one or more sites exceeded 

national median concentrations (fig. 3). Median concentrations of As, Cd, Cu, Pb, Hg, and Se in liver samples (table 2) also exceeded national median concentrations (fig. 3). The median concentration of Zn in liver 

samples was equal to the national median concentration (104 μg/g). It is worth noting that Cr, Ni, and Se 

concentrations in bed sediment and tissue were generally below national median concentrations, an indication that anthropogenic or natural sources for these 

trace elements may be more prevalent in other areas.

Trace-Element Concentrations in Bed 

Sediment and Fish Tissue

As, Cr, Pb, and Ni concentrations were higher in 

bed sediments than in fish tissue at all sample sites 

(fig. 3). Heiny and Tate (1997) also noted that As, Cr, 

and Pb concentrations were higher in bed sediments 

than in fish livers. In addition, correlations between 

most trace-element concentrations in bed sediment and 

fish tissue (liver and fillet) were not significant 

(r<±0.50, p>0.05); however, the correlation between 

Cd concentrations in bed sediment and liver tissue was 

significant (r=0.74, p<0.05). Because there are speciesspecific differences in trace-element tissue concentrations, a separate correlation analysis was performed 

only on liver samples of largescale suckers. These 

results also showed no significant correlations between 

bed sediment and liver tissue. Bonn (1999) and Heiny 

and Tate (1997) also noted poor correlations between 

most trace elements in bed sediment and fish tissue in a 

recent study of an Oregon river. Trace-element concentrations in bed sediment do not appear to be good predictors of concentrations in fish tissue. The use 

another bed sediment extraction method that de

mines bioavailable trace elements would perhap

strengthen this relation.

A comparison of the ratios of concentration

sue (liver and fillet) samples to those in bed sed

samples from the same sites illustrates those tra

ments that tend to bioaccumulate. Liver and fille

accumulated Hg and Se at higher concentration

did bed sediment (ratio >1, fig. 4). Cd tended to 

mulate in liver but not in fillet tissue. Ratios of 

Cu and Zn concentrations in liver were near 1. L

tissue accumulated all five of these trace elemen

whereas fillet tissue accumulated only Hg and S

Hg and Se are known to accumulate in muscle t

fish because these elements can be converted to 

available forms of organometallic compounds i

sediment, which can be ingested and, thus, can 

mulate in aquatic biota (Lemly, 1996; Weiner an

1996). The highest Hg concentration of 1.9 μg/

fillets of brown trout from Rock Creek near Cli

Mont. (site 2), were near the USEPA SV. Ratio

concentrations in liver tissue to those in bed sed

were among the highest of the trace-element rat

examined. Se concentrations of 24 μg/g in liver 

ples from sites 2 and 7 exceeded the toxic effec

threshold of 12 μg/g for most freshwater fish (L

1996). Concentrations of Se above this threshol

affect fish health or reproductive success. Heiny 

Tate (1997) also noted that Se concentrations w

order of magnitude higher in fish livers than in 

sediments in the South Platte River Basin in Co

Nebraska, and Wyoming. Other elements, such 

and Pb, also form organometallic compounds, b

elements did not appear to accumulate in tissue

findings are consistent with those reported for t

Willamette River Basin (Wentz and others, 199

Bonn, 1999). Although concentrations of Pb we

(>100 μg/g) in bed sediment at some NROK sit

did not tend to accumulate in fish livers or fillet

finding is particularly important because Pb has 

identified as a pollutant of concern to humans an

life as a result of mining activities in this study 

Trace-Element Concentrations Repor

Other Studies and Guidelines

The Canadian ISQG Probable Effect Levels 

(PELs), USEPA SVs, and NAWQA 1992–96 st
12 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

1,000

100

10

1.0

0.1

0.01

5,000

500

50

5

0.5

500

50

5

0.5

CONCENTRATIONS, IN MICROGRAMS PER GRAM 10,000

1,000

100

10

1.0

0.1

1,000

100

10

1.0

0.1

Figure 3. Trace-element concentrations in bed sediment and fish tissue (livers and fillets) at all sampling sites in the N

Rockies Intermontane Basins study area. [Site names shown in table 1; locations shown in figure 1. Sites are grouped 

degree of trace-element enrichment from significant natural deposits (see figure 2). Dashed lines represent National W

Quality Assessment Program median concentrations in bed sediment (number of samples, 541) and fish liver tissue (n

samples, 179) from across the Nation, 1992–96 (Rice, 1999; T. Short, U.S. Geological Survey, written commun., 1999). 

indicates no sample collected. Blanks indicate trace element was not detected in fish tissue at that site]

2 7 5 8 4 10 9 11 1 3 6 13 14

SITE NUMBER

15 16 12 2 7 5 8 4 9 11 1 3 6 13 14

SITE NUMBER

15 

500

50

5

0.5

1,000

100

10

1.0

0.1

500

50

5

0.5

1,000

100

10

1.0

0.1

5,000

500

50

5

0.5

10,000

1,000

100

10

1.0

0.1

500

50

5

0.5

0.05

Arsenic Cadmium

Chromium Copper

Lead Mercury

Trace-element

enriched

Trace-element

enriched

Trace-element

enriched

Trace-element

enriched

Trace-element

enriched

Trace-element

enriched

*

Bed sediment

 (National median)

Liver

 (National median)

Fillet

Liver

 (National median < 0.1)

*

*

*

*

*
Trace-Element Occurrence and Relative Concentra

500

50

5

0.5

CONCENTRATIONS, IN MICROGRAMS PER GRAM

1,000

100

10

1.0

0.1

Figure 3. Trace-element concentrations in bed sediment and fish tissue (livers and fillets) at all sampling sites in the N

Rockies Intermontane Basins study area—Continued.

2 7 5 8 4 10 9 11 1 3 6 13 14

SITE NUMBER

15 16 12

2 7 5 8 4 9 11 1 3 6 13 14

SITE NUMBER

15 

500

50

5

0.5

1,000

100

10

1.0

0.1

5,000

500

50

5

0.5

10,000

1,000

100

10

1.0

0.1

Nickel Selenium

Zinc

Trace-element

enriched

Trace-element

enriched

Trace-element

enriched

Bed sediment

 (National median)

Liver

 (National median)

Fillet

*

* *

results used to compare trace-element concentrations 

analyzed in this study are listed in table 3. The PEL is 

defined as the concentration above which adverse 

effects to aquatic life are predicted to occur frequently. 

The USEPA SVs were used to compare concentrations 

in bed sediment and fish fillets and are defined as those 

at which “associated adverse effects to aquatic life or 

human health are possible, but expected infrequently”

(U.S. Environmental Protection Agency, 1997). 

Because no guidelines exist for fish liver tissue, the 

USGS NAWQA 85th percentile was used to evaluate 

whether liver tissue concentrations measured for this 

study were elevated.

Concentrations of As, Cd, Cu, Pb, Hg, or Zn 

sediment exceeded the PEL at sites 1, 3, 6, 10, 

16, which are associated with mining activities a

significant mineral deposits (fig. 2, table 3). Co

tions of one or more of these trace elements at 4

cent of the sites sampled exceeded levels at whi

adverse biological effects to aquatic biota could 

This indicates potential problems with benthic o

isms that provide an important food source for 

Although this study did not address effects to st

biota directly, other studies have shown that adv

effects to aquatic biota can occur at sites in this 

area that are downstream from mining activities

at which trace-element concentrations most freq
14 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

exceeded the PEL included the upper Clark Fork (sites 

1 and 3) and the South Fork Coeur d’Alene River near 

Pinehurst (site 12). These sites are downstream from 

major past mining activities and Superfund sites. Concentrations of all trace elements except Se, for which 

no SV data are available at this time, exceeded USEPA 

SVs. However, no Se concentrations exceeded the toxicity threshold for sediment of 4 μg/g, dry weight, 

established by the National Irrigation Water Quality 

Program for the protection of aquatic life (U.S. Department of the Interior, 1998). Concentrations of one or 

more trace elements exceeded the SV at 14 of 16 sites 

sampled; concentrations at sites 7 and 9 were th

exceptions. 

On the basis of USEPA SVs, bed sediments 

of the NROK study area are enriched with trace 

ments. Both the USEPA SVs and the Canadian 

PELs are based on total concentration in bulk (t

particle-size fraction) sediment, whereas all bed 

ment samples in this study represent the <63-m

size fraction. Therefore, comparison of trace-el

concentrations in this study with PELs may resu

overestimating concentrations that adversely af

aquatic life. Deacon and Driver (1999) compare

element concentrations in the <63-micron size f

and in bulk sediment samples from mining sites 

orado. They noted that, although trace-element 

trations generally were higher in the smaller siz

tion, concentrations overall were higher in samp

from mined sites, regardless of the sediment siz

tion analyzed. 

Although many of the NROK sites exhibite

element enrichment, none of the trace-element 

trations in sportfish fillets exceeded USEPA SV

3). This is noteworthy, because Hg and Pb can b

mulate in aquatic biota and are pollutants of con

around mining sites in the study area. Accordin

Luoma (1983), the mechanisms of trace-elemen

mulation and storage in aquatic organisms are c

and diverse, varying with chemical form of the 

mode of uptake, and species. It is apparent fro

study that trace elements in bed sediment may n

readily bioavailable for uptake by some fish (fig

especially the trace elements As, Cd, Pb, Hg, an

which are known to bioaccumulate. Because bi

ability of trace elements was not specifically ad

in this study, reasons for this lack of bioavailabi

unclear; however, the cause may be low concen

of organic carbon in wetlands in the watersheds

elements in such habitats can, through various p

cesses, change to more bioavailable forms, such 

methylation of Hg into methylmercury, which t

more easily incorporated into the aquatic food c

addition, the salmonid species analyzed in this 

may be less likely to bioaccumulate some of the

elements than are other more piscivorous specie

as walleye and largemouth bass.

Even though Pb is a known health risk to hu

when ingested and has been found in fish tissue

USEPA criteria or SVs exist. Pb was detected in 

tissue samples only at sites 10, 12, and 16, all lo

in the Spokane River Basin. The highest Pb con

TISSUE CONCENTRATION/SEDIMENT CONCENTRATION

Figure 4. Distribution of ratios of trace-element concentrations

in fish tissue (livers and fillets) to concentrations in bed sediment, Northern Rockies Intermontane Basins study area.

(Ratios for nondetections were calculated by substituting the

minimum reporting level. Dashed line represents equal concentrations for tissue and bed sediment)

Arsenic

Cadmium

Lead

Nickel

Selenium

Copper

Chromium

TRACE ELEMENT

Mercury

Zinc

Livers

Fillets

1,000

100

10

1.0

0.1

0.01

0.001

0.0001

500

50

5

0.5

0.05

0.005

0.0005

1,000

100

10

1.0

0.1

0.01

0.001

0.0001

500

50

5

0.5

0.05

0.005

0.0005

Maximum

75th percentile

Median

25th percentile

Minimum
Trace-Element Occurrence and Relative Concentra

Table 3. Comparison among various trace-element guidelines and concentrations detected in bed sediment and fish tissue, Northern Rockies Intermontane Basins 

study area

[ISQGs, Canadian Interim Sediment Quality Guidelines; PEL, Probable Effect Level; USEPA SV, U.S. Environmental Protection Agency screening values for bed sediment and edible tissue (fillets); NAWQA 85th percentile, National Water-Quality Assessment Program 85th percentile for fish livers. Concentrations are in micrograms per gram, dry weight; screening values for tissue were converted to dry weight by assuming a moisture content of 74 percent, which was the mean for fish sampled in this study; na, not available; see table 1 for site names and figure 1 for site locations]

Sites with concentrations above

Guidelines Canadian PEL; USEPA SV; NAWQA 85th percentile

Canadian NAWQA Canadian

ISQGs 85th ISQGs NAWQA

PEL1 USEPA (SV)2 percentile3 PEL1 USEPA (SV) 85th percentile3

Bed Bed Fish Fish Bed Bed Fish Fish 

Trace element sediment sediment fillet liver sediment sediment fillet liver

 Arsenic . . . . . . . . . . . . . . . . . . 17 7.24 12 0.6 1, 3, 6, 12 1, 2, 3, 4, 6, 10, 11, 12, 0 1, 3, 6, 8, 11, 15, 16

13, 15, 16

Cadmium. . . . . . . . . . . . . . . . . 3.53 .68 38 3.4 1, 3, 12 11, 12 0 1, 3, 10, 12, 14Chromium . . . . . . . . . . . . . . . . 90 52.3 na 1.0 0 1, 3, 4 na 0Copper. . . . . . . . . . . . . . . . . . . 197 18.7 na 109 1, 3 1, 2, 3, 4, 5, 6, 8, 10, na 2, 11, 12

11, 12, 13, 14, 15, 16

Lead. . . . . . . . . . . . . . . . . . . . . 91.3 30.2 na .3 1, 3, 10 11, 12 1, 3, 5, 6, 10, 11, 12, na 3, 10, 11, 12, 14, 15, 16

15, 16

Mercury. . . . . . . . . . . . . . . . . . .49 .13 2.3 .4 1, 3, 12 1, 3, 6, 11, 12 0 5, 7, 10Nickel . . . . . . . . . . . . . . . . . . . 35.9 15.9 na 1.0 0 1, 3, 4, 6, 8, 10, 11, 12, na 0

13, 14, 16

Selenium . . . . . . . . . . . . . . . . . na na 192 7.1 na na 0 2, 7, 10, 11Zinc . . . . . . . . . . . . . . . . . . . . . 315 124 na 469 1, 3, 6, 12, 16 1, 3, 6, 10, 11, 12, 16 na 0

1 Canadian ISQG PELs are concentrations above which adverse effects to aquatic life are predicted to occur frequently (Canadian Council of Ministers of the Environment, 1995).2 USEPA bed sediment SVs are defined as “associated adverse effects to aquatic life or human health are possible, but expected infrequently”; USEPA tissue SVs are for protection of human health, based on 1 X 10-5 risk factor 

for an average-sized adult (70 kilograms) and a consumption rate of 6.5 grams of fish per day (U.S. Environmental Protection Agency, 1995, 1997).

3 85th percentile calculated from a total of 179 composite fish samples made up of 92 percent liver and 8 percent whole fish samples, 1992–96 (T. Short, U.S. Geological Survey, written commun., 1999).
16 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

tion (1.7 μg/g) was observed in brook trout fillets from 

the South Fork Coeur d’Alene River near Pinehurst 

(site 12). This value is well below the International 

Legal Limit of 7.7 μg/g, dry weight, established for 

removing fish from the marketplace to protect human 

health (Nauen, 1983).

One or more concentrations of As, Cd, Cu, Pb, Hg, 

or Se in liver tissue at 13 of 16 sites exceeded the 

NAWQA Program 85th percentile (table 3). None of 

the Cr, Ni, or Zn concentrations in liver tissue ex

this percentile.

RELATIONS AMONG TRACE-ELEME

CONCENTRATIONS, LAND USE, AND 

GEOLOGY

Relations Among Trace-Element Concentrations, Land Use, and Geology

Relations among trace-element concentrati

bed sediment and fish tissue and the landscape 

Table 4. Spearman’s correlation coefficients for production mine densities, significant deposit densities, and trace-elem

concentrations in fish tissue (livers and fillets) and bed sediment, Northern Rockies Intermontane Basins study area

[Mine densities and significant deposits are given for the entire area upstream from each sample site (basin) and within a 250-meter buff

streams upstream from the sample site (buffer area). Significant coefficients shown in bold (r>±0.50, p<0.05); n, number of samples]

Sample type Production Production Significant Sign

and mine density mine density deposit density depos

trace element (basin) (buffer area) (basin) (buff

Tissue

Liver (n=16)

Arsenic . . . . . . . . . . . . . . . . . . . . . 0.33 0.03 0.04 -0

Cadmium. . . . . . . . . . . . . . . . . . . . .54 .73 .75 

Chromium . . . . . . . . . . . . . . . . . . . -.62 -.71 -.62 

Copper. . . . . . . . . . . . . . . . . . . . . . .41 .07 .22 

Lead. . . . . . . . . . . . . . . . . . . . . . . . .31 .22 .19 

Mercury. . . . . . . . . . . . . . . . . . . . . -.30 -.13 .09 

Nickel . . . . . . . . . . . . . . . . . . . . . . -.12 .06 .13 

Selenium . . . . . . . . . . . . . . . . . . . . -.21 -.59 -.26 

Zinc . . . . . . . . . . . . . . . . . . . . . . . . .07 .36 .30 

 Fillet (n=15)

Arsenic . . . . . . . . . . . . . . . . . . . . . -0.01 -0.31 -0.22 -0

Cadmium. . . . . . . . . . . . . . . . . . . . .42 .42 .45 

Chromium . . . . . . . . . . . . . . . . . . . -.26 -.21 -.31 

Copper. . . . . . . . . . . . . . . . . . . . . . .24 -.05 .01 

Lead. . . . . . . . . . . . . . . . . . . . . . . . .36 .43 .49 

Mercury. . . . . . . . . . . . . . . . . . . . . -.38 -.08 -.13 

Nickel . . . . . . . . . . . . . . . . . . . . . . .14 .14 .39 

Selenium . . . . . . . . . . . . . . . . . . . . .19 -.03 .19 

Zinc . . . . . . . . . . . . . . . . . . . . . . . . .10 .01 -.09 

Bed sediment (n=16)

Arsenic . . . . . . . . . . . . . . . . . . . . . .88 .66 .70 

Cadmium. . . . . . . . . . . . . . . . . . . . .83 .61 .69 

Chromium . . . . . . . . . . . . . . . . . . . .30 .31 .26 

Copper. . . . . . . . . . . . . . . . . . . . . . .74 .62 .75 

Lead. . . . . . . . . . . . . . . . . . . . . . . . .77 .46 .61 

Mercury. . . . . . . . . . . . . . . . . . . . . .62 .39 .58 

Nickel . . . . . . . . . . . . . . . . . . . . . . .67 .68 .62 

Selenium . . . . . . . . . . . . . . . . . . . . .59 .35 .38 

Zinc . . . . . . . . . . . . . . . . . . . . . . . . .81 .64 .76 
Relations Among Trace-Element Concentrations, Land Use, and Geo

ables of land use and geology were examined. No significant correlations between land use categories and 

trace-element concentrations in either bed sediment or 

fish tissue were apparent. There were also no significant correlations between geology and trace-element 

concentrations in fish tissue. However, there were a few 

significant correlations (p<0.05) between Se (r=0.72) 

and Hg (r=0.60) concentrations in bed sediment and 

percent sedimentary rock. Because these traditional 

landscape variables of land use and geology did not 

explain the differences observed in trace-element concentrations, other measures of trace-element enrichment were explored. 

Because of the extent of mineralization in the 

NROK study area, natural conditions can affect traceelement concentrations in the environment. However, 

mining practices also can cause increased concentrations of trace elements (Axtmann and Luoma, 1991). 

Two measures of trace-element enrichment, production 

mine density and significant deposits, for each basin 

were examined in relation to trace-element concentrations in fish tissue and bed sediment (appendix A). Significant correlations (r>±0.50, p<0.05) among the tissue types, bed sediment, and trace-element enrichment 

measures are listed in table 4. In general, the determination of production mine density and significant 

deposits within stream channel buffers did not improve 

the relation between landscape variables and trace-element concentrations in tissue or bed sediment. 

Cd and Cr in liver tissue and Pb in fillet tissue were 

the only trace elements significantly correlated with 

mining measures of enrichment (r>±0.50, p<0.05). The 

negative correlations between Cr and measures of 

enrichment indicate that concentrations of this trace 

element in tissues are associated with something other 

than natural mineralization or mining. Pb in fillet tissue 

was correlated with significant deposits in the stream 

buffer but not with production mine density. 

In bed sediment, all trace elements except Cr were 

significantly correlated with one or more mining measures of enrichment. Among all correlations between 

mining measures and trace-element concentrations in 

bed sediment, basinwide production mine density and 

As, Cd, Cu, Pb, and Zn correlations produced some of 

the highest coefficients (r>0.70). Regression of mine 

density and the sum of the nine trace-element concentrations in bed sediment at each site (fig. 5) identified 

two statistically significant relations (r2=0.95 and 0.99, 

p<0.001) that respectively corresponded with the distinct groups of unenriched and enriched sites (fig. 2). 

These strong relations warrant further study usin

density as an explanatory variable for trace-elem

concentrations in bed sediment. 

Highest concentrations of As, Cd, Cu, Pb, a

(fig. 3) in sediment at sites located on the upper 

Fork (sites 1, 3, and 6) and at South Fork Coeur 

d’Alene River near Pinehurst (site 12) correspo

some of the highest production mine densities. 

centrations at these sites were 1 to 2 orders of m

tude higher than concentrations at most other sa

sites. Concentrations at the least-enriched sites 

ally were between 100 and 200 μg/g (fig. 5), wh

concentrations at enriched sites ranged from ab

300 μg/g (site 4) to more than 13,000 μg/g (site 

Sites 11 and 12, both located on the South F

Coeur d’Alene River, represent the most upstre

downstream locations in relation to the most nu

significant deposits and production mines (fig. 

enlargement). Production mine density (three m

for site 11 is depicted as high in figure 5 becaus

small basin size (18 km2), and there are no sign

deposits upstream from this site. Mine density f

12 is similar, but there are 24 significant deposi

upstream from this site, and 12 of these deposit

within the 250-m stream buffer (appendix A).

SUM OF TRACE-ELEMENT CONCENTRATIONS,

IN MICROGRAMS PER GRAM

100,000

10,000

1,000

100

0

50,000

5,000

500

50

Figure 5. Relations between production mine dens

sum of trace-element concentrations in bed sedime

ern Rockies Intermontane Basins study area. [Sam

are identified according to trace-element enrichmen

and figure 2).

0.001 0.005 0.1 0.01 0.05

Unenriched site

Enriched site

Regression line

1 3

6

1

10

4

15

16

5 8

7 14

9

2

13

r2 = 0.99

p < 0.001

n = 7

r2 = 0.95

p < 0.001

n = 9

PRODUCTION MINES PER

SQUARE KILOMETER
18 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

Enrichment measures of significant deposits and 

production mine density generally were helpful for 

explaining the increased trace-element concentrations 

observed in bed sediment. In this study, however, 

enrichment resulting from natural mineralization and 

enrichment resulting from mining activities could not 

be differentiated. For future evaluations, if some sample sites could be found in basins that contain natural 

mineral deposits but are not influenced by past or current mining activities, trace-element concentrations in 

these two types of enriched areas could be compared. 

SUMMARY

Summary

All nine trace elements evaluated for this report 

were detected in all bed sediment samples; however, 

not all trace elements were present above detection levels in fish tissue. Median concentrations of Cd, Cu, Se, 

and Zn were significantly higher in liver tissue than in 

fillet tissue.

Sites 1, 3, 4, 6, 10, 12, and 16 are considered 

enriched with trace elements relative to other sample 

sites on the basis of significant deposits summarized 

for each basin. Concentrations of As, Cd, Cu, Pb, Hg, 

and Zn in bed sediment were highest at these enriched 

sites. Concentrations of trace elements in fish tissue 

generally did not show this same pattern, except for 

high Cd concentrations in liver tissue and the detection 

of Pb in fillet tissue. Bed sediment from the South Fork 

Coeur d’Alene River contained the highest concentrations of Cd, Pb, Hg, and Zn. Fish tissue at this site also 

contained the highest concentrations of Cd, Pb, and Zn. 

Some concentrations at this site exceeded the national 

median by several orders of magnitude. Concentrations 

of Cu in bed sediment from the upper Clark Fork 

exceeded the national median. Results from this study 

indicate that concentrations of some trace elements in 

bed sediment and liver tissue of fish from NROK 

streams generally are higher than national median concentrations in sediment and fish tissue determined from 

the NAWQA Program, 1992–96.

Correlations between most trace-element concentrations in bed sediment and tissue (livers and fillets) 

were poor; however, there was a significant correlation 

between Cd in bed sediment and liver tissue. Trace-element concentrations in bed sediment did not appear to 

be good predictors of concentrations in tissue.

Liver and fillet tissues accumulated Cd, Cu, Hg, 

Se, and Zn at higher concentrations than did bed sediment. All five of these elements were detected at high 

concentrations in liver tissue, whereas only Hg 

were found at detectable levels in fillet tissue. C

trations of Se in liver tissue relative to bed sedim

were higher than any of the other four elements

Although concentrations of Pb in bed sedim

were high at some sites, Pb did not tend to accu

in fish livers or fillets. This finding is particular

important because Pb has been identified as a p

of concern to humans and wildlife as a result of 

activities in this study area.

Concentrations of As, Cd, Cu, Pb, Hg, or Zn 

sediment exceeded the PEL primarily at sites as

ated with significant deposits and (or) mining ac

Concentrations of one or more of these trace ele

at 44 percent of the sites sampled exceeded leve

which adverse biological effects to aquatic biot

occur. This indicates potential problems for the 

organisms that provide an important food sourc

fish. Sites at which concentrations most frequen

exceeded the PEL included the upper Clark For

the South Fork Coeur d’Alene River near Pineh

downstream from major past mining activities. 

centrations of one or more trace elements excee

SV at 14 of 16 sites sampled. 

Even though many of the sites exhibited tra

ment enrichment, no trace-element concentratio

sportfish fillets exceeded USEPA SVs. This is n

thy, because Pb and Hg can bioaccumulate in aq

biota and are pollutants of concern around mini

in the study area. It is apparent from this study 

trace elements in bed sediment are not readily b

able for uptake by fish, especially the trace elem

As, Cd, Pb, Hg, and Se, which are known to bio

mulate in aquatic food chains. One or more con

tions of As, Cd, Cu, Pb, Hg, or Se in liver tissue 

16 sites exceeded the NAWQA Program 85th p

tile.

No significant correlations between land us

gories and trace-element concentrations in eithe

sediment or fish tissue were apparent. There we

no meaningful significant correlations between 

ogy and trace-element concentrations in fish tis

Most trace-element concentrations in tissue did 

correlate with significant deposits or production 

density. In bed sediment, all trace elements exc

were significantly correlated with one or more m

measures of enrichment. Correlations between 

tion mine density and As, Cd, Cu, Pb, and Zn pr

some of the highest coefficients (r>0.70). Highe

trace-element concentrations at sites located on 
References C

upper Clark Fork and South Fork Coeur d’Alene River 

corresponded to some of the highest production mine 

densities; concentrations were 1 to 2 orders of magnitude higher than at most other sample sites.

Regression of production mine density and the sum 

of trace-element concentrations in bed sediment identified two statistically significant relations (r2=0.95 and 

0.99, p<0.001) that respectively corresponded with the 

distinct groups of unenriched and enriched sites. These 

strong relations warrant further study using mine density as an explanatory variable to predict trace-element 

concentrations in bed sediment. 

For future evaluations, if some sample sites could 

be found in basins that contain natural mineral deposits 

but are not influenced by past or current mining activities, trace-element concentrations in these two types of 

enriched areas could be compared. 

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SUPPLEMENTAL INFORMATION

Supplemental Information

Appendix A. Hard-rock mining activities in the Northern Rockies Intermontane Basins study area and within a 250-meter buffer area along perennial streams in each subbasin[Production mines are locations where active and past mineral commodities were extracted. Sand and gravel mines are not included. Data were taken from the Minerals Availability System, compiled by the U.S. Bureau of Mines (1995). Significant mineral deposits of the United States, including gold, silver, copper, lead, and zinc, were identified in the U.S. Geological Survey data base (Long and others, 1998); No., number; km2, square kilometers; m, meters]

 Basin Buffer (250 m)

Predominant Production Significant Production Significant

Site commodities mines Production deposits Significant mines Production deposits Significant

No. mined (1,353)a mines/km2 (66)a deposits/km2 (660)b mines/km2 (31)b deposits/km2

1 Manganese, gold, silver . . . . . . . 149 0.0860 6 0.0030 42 0.0590 2 0.00282 Gold, silver, sapphires . . . . . . . . 20 .0090 1 .0004 11 .0120 0 03 Gold, manganese, silver. . . . . . . 433 .0450 20 .0021 186 .0500 7 .00194 Gold, lead, silver . . . . . . . . . . . . 36 .0290 7 .0056 23 .0380 6 .00985 Gold, silver, copper . . . . . . . . . . 51 .0070 0 0 27 .0100 0 06 Gold, silver, copper . . . . . . . . . . 666 .0240 31 .0011 333 .0300 14 .00137 Copper, coal . . . . . . . . . . . . . . . . 5 .0020 0 0 0 0 0 08 Copper, gold, silver . . . . . . . . . . 50 .0020 1 .0001 21 .0020 0 09 Lead, silver, gold . . . . . . . . . . . . 19 .0080 0 0 13 .0140 0 0

10 Lead, gold, silver . . . . . . . . . . . . 62 .0270 5 .0022 28 .0330 4 .004611 Copper, lead, silver . . . . . . . . . . 3 .1680 0 0 0 0 0 012 Lead, silver, gold . . . . . . . . . . . . 172 .2330 24 .0325 102 .4170 12 .049013 Gold, copper. . . . . . . . . . . . . . . . 3 .0110 0 0 3 .0340 0 014 Gold, copper, lead . . . . . . . . . . . 18 .0070 0 0 13 .0140 0 015 Stone, clay, tungsten . . . . . . . . . 42 .0240 0 0 31 .0260 0 016 Lead, stone, silver . . . . . . . . . . . 349 .0270 29 .0022 182 .0400 16 .0035

a Total number in study area upstream from site 16.b Total number in study area stream buffers upstream from site 16.

Supplemental Inform
26 Trace Elements in Fish Tissue and Streambed Sediment, Washington, Idaho, and Montana, 1998

Appendix B. Species, sizes, and tissue types of fish collected in the Northern Rockies Intermontane Basins study are

[Site locations shown in figure 1; names shown in table 1; No., number; mm, millimeters; g, grams]

No. Total Mean

Site Tissue of length length W

No. Species type fish (mm) (mm) 

1 Largescale sucker. . . . . . . . . . . . . . . liver 8 428–615 512 72

Mountain whitefish . . . . . . . . . . . . . fillet 5 350–412 386 45

Brown trout . . . . . . . . . . . . . . . . . . . fillet 5 376–426 400 46

2 Brown trouta. . . . . . . . . . . . . . . . . . . liver 7 352–478 410 45

Brown trouta. . . . . . . . . . . . . . . . . . . fillet 7 352–478 410 45

3 Largescale sucker. . . . . . . . . . . . . . . liver 8 422–531 451 70

Largescale sucker. . . . . . . . . . . . . . . liver 8 440–536 477 77

Largescale sucker. . . . . . . . . . . . . . . liver 8 430–520 481 76

Mountain whitefish . . . . . . . . . . . . . fillet 6 325–376 350 39

4 Largescale sucker. . . . . . . . . . . . . . . liver 8 407–551 467 7

Mountain whitefish . . . . . . . . . . . . . fillet 4 260–335 282 15

5 Mountain whitefisha. . . . . . . . . . . . . fillet 8 280–340 318 20

Mountain whitefisha. . . . . . . . . . . . . liver 17 280–350 317 20

6 Largescale sucker. . . . . . . . . . . . . . . liver 6 440–580 505 1,02

Mountain whitefish . . . . . . . . . . . . . fillet 5 310–385 331 25

7 Mountain whitefisha. . . . . . . . . . . . . liver 8 295–404 337 22

Mountain whitefisha. . . . . . . . . . . . . fillet 8 295–404 337 22

Mountain whitefisha. . . . . . . . . . . . . fillet 8 295–404 337 22

8 Largescale sucker. . . . . . . . . . . . . . . liver 6 445–490 463 94

Mountain whitefish . . . . . . . . . . . . . fillet 6 270–330 303 18

9 Largescale sucker. . . . . . . . . . . . . . . liver 8 375–468 428 44

10 Mountain whitefisha. . . . . . . . . . . . . liver 7 282–415 332 23

Mountain whitefisha. . . . . . . . . . . . . fillet 7 282–415 332 23

11 Rainbow trouta,b. . . . . . . . . . . . . . . . liver 7 250–330 300 16

Rainbow trouta,b. . . . . . . . . . . . . . . . fillet 7 250–330 300 16

12 Brook trouta . . . . . . . . . . . . . . . . . . . liver 6 215–325 298 14

Brook trouta . . . . . . . . . . . . . . . . . . . fillet 6 215–325 298 14

13 Cutthroat trouta . . . . . . . . . . . . . . . . liver 8 261–374 322 18

Cutthroat trouta . . . . . . . . . . . . . . . . fillet 8 261–374 322 18

14 Largescale sucker. . . . . . . . . . . . . . . liver 8 445–540 485 82

Mountain whitefish . . . . . . . . . . . . . fillet 8 210–324 292 2

15 Largescale sucker. . . . . . . . . . . . . . . liver 8 365–497 445 47

Rainbow trout . . . . . . . . . . . . . . . . . fillet 5 225–260 239 12

16 Largescale sucker. . . . . . . . . . . . . . . liver 8 430–500 471 79

Rainbow trout . . . . . . . . . . . . . . . . . fillet 5 330–460 366 39

a Same fish used for analysis.

b Hatchery fish.
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