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Evaluation of Metals in Bullhead, Bass, and Kokanee from Lake Coeur D'Alene



The 2001 Human Health Risk Assessment for the Coeur d'Alene Basin indicated that more information was neededabout fish in Lake Coeur d'Alene (TerraGraphics. 2001). The Coeur d'Alene Tribe and a collaborative inter-agencyteam agreed. As a result, these groups cooperatively conducted a study to determine the contaminant levels in fishfrom Lake Coeur d'Alene. The Agency for Toxic Substances and Disease Registry (ATSDR) and the IdahoDepartment of Health and Welfare, Idaho Division of Health (IDOH) were asked to review the data from this studyand evaluate the potential health risks for tribal and recreational fishers that may result from consumption of threefish species found in Lake Coeur d'Alene.

Fish were collected in May and August 2002, and analyzed for 18 metals (Table 1). Fish were collected at about the same time of year, and in areas used by tribal and recreational fishers. Fillet and gutted whole carcass samples were selected to represent the two major portion types used by both subsistence and sport/recreational fishers. Based on extensive discussions about use by tribal and sport/recreational fishers, ecological importance, relevance to other species, and patterns of exposure to contaminants, the three fish species selected were bass (mostly largemouth bass, Micropterus salmoides), bullhead (mostly brown bullhead, Ictalurus nebulosus), and kokanee (Oncorhynchus nerka). This health consultation evaluates the potential for adverse health effects associated with consuming these fish species.

Table 1.

Eighteen metals analyzed in Coeur d'Alene Fish Samples (USEPA 2003).
Antimony (Sb)Cobalt (Co)Nickel (Ni)
Arsenic (As)Copper (Cu)Selenium (Se)
Barium (Ba)Lead (Pb)Silver (Ag)
Beryllium (Be)Mercury (Hg)Thallium (Tl)
Cadmium (Cd)Manganese (Mn)Vanadium(V)
Chromium(Cr)Molybdenum(Mo)Zinc (Zn)


To conduct this evaluation, ATSDR and IDOH worked jointly with a collaborative inter-agency group todevelop and implement the Lake Coeur d'Alene Fish Investigation. The investigation plan was preparedby the U.S. Environmental Protection Agency (USEPA 2002a) and approved by IDOH, ATSDR, USEPARegion 10, the Coeur d'Alene Tribe, Idaho Department of Fish and Game (IDFG), Idaho Department ofEnvironmental Quality (IDEQ) and the U.S. Fish and Wildlife Service. The approval signatures on thesampling plan indicated that the entities participated in the development of the plan and believed ittargeted the appropriate species and locations within Lake Coeur d'Alene to assess human health implications of consuming fish from the lake.


Historical mining practices in the Coeur d'Alene Basin have resulted in contamination of soil, sediment, surface water, and groundwater. Currently, substantial portions of the Coeur d'Alene Basin containelevated concentrations of contaminants that are hazardous both to humans and to plants and animals(collectively termed ecological receptors). To evaluate and address the effects of mining contaminationin the Basin, USEPA conducted a remedial investigation and feasibility study (URS Greiner and CH2MHill 2001a, 2001b) and issued a Proposed Plan (USEPA 2001b) for cleanup of the Basin in October 2001. Following evaluation of public comments, USEPA issued a Record of Decision (ROD) in September of 2002 (USEPA 2002b).

The Bunker Hill Mining and Metallurgical Complex Operable Unit 3 (Coeur d'Alene Basin) ROD notedthat questions about potential risks from eating whole fish or fillets from Lake Coeur d'Alene needsfurther evaluation (USEPA 2002b). Previous evaluations of fish tissue from Lake Coeur D'Alene havenot included whole fish, and only limited numbers of fillets have been sampled. As a result, someuncertainty exists about the risks from eating fish caught in Lake Coeur d'Alene. The ROD also notedthat collaborative fish investigations are being implemented to address data gaps regarding fish in LakeCoeur d'Alene.

In support of the ROD, human health (TerraGraphics 2001; CH2M Hill and URS Greiner 2001) andecological (CH2M Hill and URS Greiner 2001) risk assessments were completed as part of the remedialinvestigation/feasibility study. The primary metals of concern identified include lead and arsenic forhuman health, and cadmium, lead, and zinc for ecological receptors. The human health risk assessmentconcluded that available data on contaminant concentrations in fish in Lake Coeur d'Alene areinsufficient to quantify potential risks (TerraGraphics 2001).

The uncertainty section of the human health risk assessment indicated that potential exposure tocontaminants from consumption of fish taken from Lake Coeur d'Alene has not been quantified. Whilesubstantial fillet data for three species are available for the lateral lakes, these data do not accuratelyrepresent risks for persons practicing a subsistence lifestyle in which other tissues, organs, or whole fishare consumed. Metal concentrations in fillets tend to be lower than metal concentrations in other fishorgans or in whole body fish. Use of fillet data typically under-estimate risks for a subsistence lifestyle(TerraGraphics 2001).

Available fillet data for the lateral lakes was obtained from specimens too small for quantifying humanhealth risks from consuming fish from Lake Coeur d'Alene. The species collected in the lateral lakeswere not considered to be sufficiently representative for quantifying human health risks from Lake Coeurd'Alene fish. While risks were not found for sport/recreational fishers in the lateral lakes, their risks fromconsuming Lake Coeur d'Alene species could not be quantified using the existing data (TerraGraphics2001). Nor do the lateral lakes data address concerns about subsistence consumption of fish from LakeCoeur d'Alene.

In addition to information provided in the human health risk assessment, the Coeur d'Alene Tribe has alsoidentified the lack of data on fish in Lake Coeur d'Alene as a data gap (Coeur d'Alene Tribe 2001). Thetribe submitted a preliminary fish sampling plan to EPA, portions of which were incorporated in the FishInvestigation Plan (USEPA 2002a).

ATSDR has examined lead issues in and around Lake Coeur d'Alene since 1989. Issues have included the relationship of lead and cadmium levels with fish consumption (ATSDR 1989), risk factors for elevated blood lead levels in children (ATSDR 1995), health effects in female former smelter workers (ATSDR 1997a), and lead exposures in current and previous residents (ATSDR 1997b). ATSDR has evaluated metals in fish from the lateral chain lakes (ATSDR 1998) and in soils of residential properties in the panhandle counties of Benewah, Kootenai and Shoshone (ATSDR 2000a). ATSDR also reviewed a preliminary fish sampling plan (Coeur d'Alene Tribe 2001) and the Fish Investigation Plan prepared by USEPA (2002a).


Collection of fish from Lake Coeur d'Alene was performed in accordance with the Fish InvestigationPlan (USEPA 2002a). This plan was collaboratively developed and detailed the protocol to be followedduring collection of fish from the lake, shore processing of fish, and processing of fish samples at thelaboratories.

The three species selected for capture and analysis were kokanee (Oncorhynchus nerka), largemouth bass(Micropterus salmoides), and bullheads (Ictalurus sp.) Based on input from IDFG, ATSDR, and others,these species were targeted for this investigation because of their use by both tribal and sport/recreationalfishers. Tribal subsistence fishers extensively consume all three species, and a sport/recreational fisheryexists for all three species. These three species are also of ecological importance to the Lake Coeurd'Alene fishery. They encompass a variety of feeding habits and home ranges, thus likely have differentexposure patterns to contaminants.

Kokanee primarily feed on plankton found in the water column and range throughout the lake. The largehome range of kokanee means that they should be good integrators of contaminant concentrationsthroughout Lake Coeur d'Alene. Largemouth and smallmouth bass are predatory on other fish, and haverelatively small home ranges compared to kokanee. Bass should be more indicative of contaminants inlocalized areas of the lake. Bullhead species are mostly bottom feeders, usually associated closely withbottom sediments, and are not considered highly mobile. They should also help identify sediment-associated contaminants in localized areas of the lake.

Sampling locations on the lake are shown in Figure 1. The three specific Lake Coeur d'Alene locations targeted for fish sampling in this effort were:

Northern end of lake (Mica Bay to Wolf Lodge Bay)
Central basin (mouth of Coeur d'Alene River north to Driftwood Point)
Southern basin (lake areas at least 1 mile south of the mouth of the Coeur d'Alene River)

Recreational and subsistence fish consumers use all three sampling locations. These locations alsoprovide a geographically balanced sampling of the lake. Statistically significant sample sets of bullheadand bass were collected from all three locations. Because of the difficulty in collecting suitable numbersof kokanee from all three sampling locations, the lake was treated as a single sampling station for thisspecies (USEPA 2003).

The two sample types obtained were gutted carcass and fillet. For gutted carcass samples, the caudal (tail)fin, gills, and guts, with the exception of the kidney, were removed. Gutted, whole-fish carcass sampleswere collected to represent the most common preparation method for fish which are smoked, canned, orused in soups and stews. Fillet samples were collected to represent a portion commonly consumed by sport, recreational and tribal fish consumers.

Lake Coeur d'Alene
Figure 1. Lake Coeur d'Alene


One of the most important steps in assessing exposure to contaminants in the environment is to estimatethe amount of a chemical to which people could be exposed (ATSDR 1992). For non-cancer healthconcerns, this is typically done by using the building blocks shown in the following calculation:

Estimated Exposure Dose (EED) equals Contaminant Concentration (CC) times Ingestion Rate (IR) times Annual Exposure Factor (AEF) times Absorption Factor (AF) divided by Body Weight (BW)

The estimated exposure dose (EED) may also be referred to as the annual exposure dose, and is calculated fromavailable site specific information. In this health consultation, contaminant concentration (CC) refers to the metalconcentrations reported for fish samples from Lake Coeur d'Alene by USEPA (2003).

The amount of fish that people eat is referred to as ingestion rate (IR) and may also be called consumption rate.Frequency and duration of exposure on a yearly basis are expressed as an annual exposure factor (AEF) to makecalculations easier. The amount of a specific metal that is absorbed by people eating fish is estimated by using anabsorption factor (AF). Estimated body weight (BW) for people consuming fish is the denominator of the equation.

The basic formula above is used to estimate the exposure dose for non-carcinogenic effects. For assessing cancer,the lifetime excess cancer risk calculation assumes a 70 year exposure period and is calculated as follows:

Estimated Annual Exposure Dose (mg/kg/day) Cancer Slope Factor (mg/kg/day -1)

Excess cancer risk for an exposure less than an entire lifetime is calculated using the following equation:

(Estimated Annual Exposure Dose Cancer Slope Factor) No. of Years Exposed
70 year lifetime

A typical less than lifetime exposure period is the residence time in the community where the exposure occurred.Two residence times typically used are 30 years for maximum time at one residence and 9 years for the median timeat one residence (USEPA 1997).

Metal Concentrations in Fish

Eighteen metals (Table 1) were analyzed in three fish species collected from Lake Coeur d'Alene by USEPA (2003).Bullhead specimens were collected from all three sampling areas. The highest average values for arsenic and leadwere found in the bullhead gutted carcass samples from the center lake sampling area (Table 2).

Bass specimens were collected from all three sampling areas. Results for bass gutted carcass samples were reportedfrom all three lake sampling areas. Bass fillet samples were collected only in the center lake sampling area. Thehighest average mercury concentration (0.188 ppm) reported by USEPA (2003) was found in bass fillets (Table 2).

A limited number of kokanee samples were collected. Because of the highly mobile nature of kokanee, sampleresults were not divided by lake area. A lake-wide average was calculated for gutted carcass and fillet samples.

Average concentrations for arsenic, cadmium, lead, and mercury are shown in Table 2. Included are averageconcentrations for the three lake sampling areas shown in Figure 1 (north, center and south), the overall average foreach fish species analyzed, and an estimated average for each metal by sample type (gutted carcass and fillet). Metalconcentrations were typically higher in gutted carcass samples than in fillets with the exception of mercury (Table 2). Appendix A and B both show additional data for As, Cd, Pb and Hg. Other metals are summarized in Appendix C.

For our initial evaluation, the highest concentration for each metal reported by USEPA (2003) was used to determineworst case exposure conditions. If this indicated that no problems were likely from exposure to a specific metal, thenthat metal was ruled out as a contaminant of concern and not evaluated further. If our worst case scenario evaluationindicated a potential problem, then further, more detailed evaluations were done and the maximum average concentration was used.

Table 2.

Summary of average arsenic, cadmium, lead and mercury results (mg/kg, wet weight) for fish samples from Lake Coeur d'Alene (USEPA 2003).
  Gutted Carcass Samples Fillet Samples
Fish Species and Sampling Location Arsenic
Arsenic Cadmium Lead Mercury
Bass–North 0.126 0.021 0.156 0.174 - - - -
Center 0.115 0.008 0.197 0.171 0.064 0.015 0.020 0.188
South 0.146 0.015 0.034 0.111 - - - -
Lake Average 0.129 0.015 0.129 0.152 0.064 0.015 0.020 0.188


Kokanee (Entire Lake) 0.145 0.139 0.115 0.075 0.083 0.018 0.020 0.092


Bullheads–North 0.072 0.034 1.42 0.028 0.024 0.006 0.029 0.038
Center 0.218 0.077 3.85 0.045 0.116 0.016 0.232 0.065
South 0.05 0.020 0.479 0.052 0.028 0.005 0.026 0.063
Lake Average 0.113 0.044 1.92 0.042 0.056 0.009 0.096 0.055
Overall Lake Average 0.125 0.045 0.893 0.094 0.063 0.012 0.065 0.089

Fish Ingestion Rates

The amount of fish eaten by people can be difficult to accurately estimate. It can vary by age, sex, lifestyle, or health status. Fish consumption rates used in this health consultation were provided by the Coeur d'Alene Tribe; IDOH, IDFG, and IDEQ; and by USEPA (Table 3). They cover a wide, but reasonable, range of fish-eating habits that reflect various lifestyles of people who eat fish from Lake Coeur d'Alene. These lifestyles include traditional and contemporary tribal subsistence fish consumers, and sport, recreational or incidental fish consumers. Consideration was also given to fish consumption rates that reflect resident and tourist lifestyles.

To estimate exposures, consistent units are used to describe fish consumption for the purpose of making the calculations. To do this, units of grams per day (g/d) are typically used. Because many people think of their fish consumption in other terms, Table 3 compares fish consumption rates expressed in different ways, including number of fish meals per month. Our calculations were made with (1) portion sizes used by IDOH (adults: 227 grams/meal, 8 oz.; children 114 grams/meal, 4 oz.) and (2) using 30.44 days per month.

The number of fish meals eaten per month can vary widely depending on age, lifestyle and other factors. The information in Table 3 is provided to compare the numbers used solely for calculating exposure doses (grams/day) with other ways, including meals/month, which people may think about fish consumption. Also, IDOH provides guidance in fish consumption advisories based on meals/month. Adults eating 72 eight-ounce fish meals/month or children eating more than 90 four-ounce meals/month is very unlikely, however, these are provided to show how many fish meals/month would be needed to eat 540 grams of fish /day.

Table 3.

Fish consumption rates compared in equivalent units and amounts.*
Consumer type Grams, kilograms and ounces per day Grams, kilograms and ounces per month Meals per month Lbs/year
Recreational Fish Consumer 46g; 0.046kg; 1.6oz 1,400g; 0.140kg; 49oz 6 (adult)
12 (child)
Recreational Fish Consumer 65g;0.065kg 2.3oz 1,979g; 0.198kg; 70oz 8-9 (adult)
17 (child)
Contemporary Subsistence Fish Consumer 170g; 0.170kg; 6oz 5,175g; 0.518kg; 182oz 22-23 (adult)
45 (child)
Traditional Subsistence Fish Consumer 540g; 0.540kg; 19oz 16,438g; 1.644kg; 579oz 72 (adult)
>90 (child)

* Note that meals per month are based on an 8 oz (227 g) portion size for adults and a 4 oz (114 g) portion size for children. Using a different portion size would change the number of meals per month.

Of course not every adult may eat an 8 oz portion size, or every child a 4 oz portion size. These are standard portions sizes used for calculation purposes. They are also often used by many states to relay fish consumption advisory information to the general public.

Annual Exposure Factors

An annual exposure factor of one represents someone who consumes a given amount of fish every day of the year. This typically is used to consider worst case exposure scenarios, and is often used to assess exposures to subsistence consumers. Using an annual exposure factor eases the calculation burden, and provides another way to explain exposure duration and frequency. Table 4 shows a range of annual exposure factors that reflect different exposure frequencies and durations. These are provided to help show how frequency and duration of exposure are included in calculations of exposure estimates. It is important to note that only two annual exposure factors were used in this consultation. An annual exposure factor of one (365 days per year) was used for all exposure estimates except those for non-residents. For non-resident exposures, an annual exposure factor of 0.28 (104 days per year) was used.

Table 4.

Range of annual exposure factors.
Exposure Exposure Frequency Exposure Duration Number of Days Exposure Occurs Annual Exposure Factor
Daily 1
12 months
9 months
6 months
Five days per week 5/7 (= 0.71)
12 months
9 months
6 months
Two days per week 2/7 (= 0.28)
12 months
9 months
6 months
One day per week 1/7 (= 0.14)
12 months
9 months
6 months

Note: 30.44 days per month used for calculations. Only annual exposure factors of 1 and 0.28 were used in this health consultation.

Bioavailability and Absorption Factors

In estimating exposure doses, cadmium, lead, selenium and zinc measured in fish samples were assumed to be completely (100 percent) available. This is reflected in our calculations by using an absorption factor (AF) of 1. Thus, the total values for these four metals were used as they were reported by USEPA (2003). We used this assumption because the actual bioavailability of these metals in fish to humans, while likely to be less than 100%, is difficult to measure and often not known.

For mercury, the total values reported by USEPA (2003) were assumed to be all methyl mercury. Because this form of mercury is highly bioavailable to humans, we assumed that the total mercury values reported by USEPA (2003) were 100% bioavailable. To reflect this in our calculations, we used an absorption factor of 1.

For the total arsenic levels reported by USEPA (2003), we conservatively assumed that 20% was inorganic arsenic, the most toxic form. Fish can absorb inorganic arsenic from water or sediment, and rapidly convert most of it to organic forms. This is a natural process and many fish and shell-fish have high levels of organic arsenic. Organic forms of arsenic are not harmful to people because they are easily and quickly eliminated through the urine. An absorption factor of 0.20 was used to reflect inorganic arsenic levels in our calculations.

Body Weight

We used a body weight of 70 kg (154 lbs.) for adult men and women (including pregnant women) in our calculations (ATSDR 1992). This is a slightly lower body weight than routinely used by the IDOH (80 kg) and makes our exposure estimates a bit more conservative. For children, the body weight used varies from 10 kg (22lbs.) to 35 kg (77lbs) depending on age group. Table 5 shows adult and child body weights used by ATSDR and IDOH. In this consultation, we used a 10 kg body weight for children, (instead of 16 kg or 35 kg), adding to the conservative nature of our evaluation.

Table 5.

Body weights for children and adults.
  Body Weights
Children ATSDR Idaho
1 yr old child 10 kg (22 lbs) ----
2-6 yr old children 16 kg (35 lbs) 20 kg (44 lbs)
7-14 yr old 35 kg (77 lbs) ----
Adults ATSDR Idaho
General Population 70 kg (154 lbs) 80 kg (176 lbs)
Pregnant Women 70 kg 70 kg

Now that all the individual components of the exposure dose calculation have been presented, the equation shown earlier in this section is given below with abbreviations and units:

EED (mg/kg/day) = CC (mg/kg) IR (kg/day) AEF (1 or 0.28) AF (usually 1)
BW (kg)

Ingestion rate is shown here as kg/day to eliminate converting between grams (g) and milligrams (mg). Inverting thedenominator (1/BW) and multiplying solves the equation. The result is an estimated exposure dose (EED) expressedas mg of contaminant per kg of body weight per day. This is how estimated exposure doses were calculated for thisconsultation.


Our initial evaluation used conditions that reflect worst case exposures to clearly determine which metals are not ofconcern and identify metals needing further evaluation. Using this approach, metals that do not present a problemunder worst case exposure conditions would not be expected to be of concern under more typical exposureconditions. Our worst case evaluations used the highest concentration for each metal reported by USEPA (2003), themaximum fish consumption rate (540 grams/day) to represent traditional subsistence exposure, an annual exposurefactor of 1 (365 days/year) and an absorption factor of 1 (100%). Bioavailability was assumed to be 100%. Foradults, a body weight of 70 kg was used and for children a body weight of 10 kg was used. This conservativeevaluation resulted in 14 of the 18 metals reported by USEPA (2003) being ruled out from further consideration.Antimony, beryllium and thallium were eliminated from further consideration because they were not detected.Details on the other 11 metals eliminated as contaminants of concern are provided in Appendix C.

Arsenic, cadmium, lead, and mercury were identified as the primary metals of concern. Each of these metals is givenfurther, more detailed, consideration in the following Discussion section. Additional information on arsenic, cadmium, lead, and mercury is provided in Appendix D.

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