Determination of Total Mercury in 

Whole-Body Fish and Fish Muscle

Plugs Collected from the South Fork

of the Humboldt River, Nevada,

September 2005

Prepared in cooperation with the U.S. Bureau of Reclamation

U.S. Department of the Interior

U.S. Geological Survey

Open-File Report 2007–1059

Determination of Total Mercury in Whole-Body Fish and 

Fish Muscle Plugs Collected from the South Fork of the 

Humboldt River, Nevada, September 2005 

By Thomas W. May and William G. Brumbaugh

Prepared in cooperation with the U.S. Bureau of Reclamation 

Open-File Report 2007–1059 

U.S. Department of the Interior 

U.S. Geological Survey 
U.S. Department of the Interior 

DIRK KEMPTHORNE, Secretary 

U.S. Geological Survey 

Mark D. Myers, Director 

U.S. Geological Survey, Reston, Virginia 2007 

For product and ordering information: 

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Telephone: 1-888-ASK-USGS 

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its natural and living resources, natural hazards, and the environment: 

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Suggested citation:

May, T.W., and Brumbaugh, W.G., 2007, Determination of total mercury in whole-body fish and fish muscle plugs 

collected from the South Fork of the Humboldt River, Nevada, September 2005: U.S. Geological Survey Open-File 

Report 2007–1059, 4 p. 

Any use of trade, product, or firm names is for descriptive purposes only and does not imply 

endorsement by the U.S. Government. 

Although this report is in the public domain, permission must be secured from the individual 

copyright owners to reproduce any copyrighted material contained within this report. 
Contents 

Abstract.....................................................................................................................................................................................................................1 

Introduction...............................................................................................................................................................................................................1 

Sample History .........................................................................................................................................................................................................1 

Methods.....................................................................................................................................................................................................................2

Muscle Plugs, Homogenization and Lyophilization .......................................................................................................................................2 

Instrumental Analysis and Data Reporting .....................................................................................................................................................2

Results and Discussion...........................................................................................................................................................................................2

Quality Control..........................................................................................................................................................................................................3 

References Cited......................................................................................................................................................................................................4

Tables 

1. Total mercury concentrations in whole-body fish and fish muscle plugs from the South Fork of the Humboldt River, 

Nevada, 2005 ............................................................................................................................................................................................3 

2. Total mercury concentrations in dry tissue powders submitted with whole-body fish samples, 2005 ....................................3 

Conversion Factors 

Multiply By To obtain 

Mass 

gram (g) 0.03527 ounce (oz) 

milligram (mg) .000035 ounce (oz) 

Length 

millimeter (mm) 0.0394 inches (in) 

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

°F=(1.8×°C)+32 

Concentrations of chemical constituents in solid materials are given in microgram per gram (μg/g). 

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Determination of Total Mercury in Whole-Body Fish and 

Fish Muscle Plugs Collected from the South Fork of the 

Humboldt River, Nevada, September 2005 

By Thomas W. May and William G. Brumbaugh 

Abstract 

This report presents the results of a study by the U.S. Geological Survey, done in cooperation 

with the U.S. Bureau of Reclamation, to determine mercury concentrations in whole-body fish and fish 

muscle plugs from the South Fork of the Humboldt River near Elko in the Te-Moak Indian Reservation. 

A single muscle plug was collected from beneath the dorsal fin area in each of the three whole-body fish 

samples. After homogenization and lyophilization of the muscle plugs and whole-body fish samples, 

mercury concentrations were determined with a direct mercury analyzer utilizing the process of thermal 

combustion-gold amalgamation atomic absorption spectroscopy. Mercury concentrations in whole-body 

fish ranged from 0.048 to 0.061 microgram per gram wet weight, and 0.061 to 0.082 microgram per 

gram wet weight in muscle plugs. All sample mercury concentrations were well below the U.S. 

Environmental Protection Agency’s fish consumption advisory of 0.30 microgram per gram wet weight. 

Introduction 

The U.S. Geological Survey (USGS) conducted a study in cooperation with the U.S. Bureau of 

Reclamation (USBR) to determine the concentrations of mercury in whole-body fish and fish muscle 

plugs from the South Fork of the Humboldt River near Elko in the Te-Moak Indian Reservation. The 

whole-body fish mercury data represents the total mercury body burden available to wildlife fish 

consumers; whereas the fish muscle plug data are used to evaluate human consumption risks. The 

USBR will use the data from this study to make future management decisions concerning fish harvests 

from the South Fork of the Humboldt River. The data will be provided to state and local agencies 

responsible for evaluating the potential risk to the public from fish consumption. Fish health advisories 

will be issued if necessary. 

Sample History 

A shipment of five samples was received by the Inorganic Chemistry section of the USGS on 

October 21, 2005. Three whole-body fish and two tissue powder samples were collected by USBR on 

September 30, 2005. Upon receipt, the samples were assigned USGS batch number 1212 and USGS 

identification numbers 35336–35340. 

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Methods 

Muscle Plugs, Homogenization and Lyophilization 

After partial thawing, a single muscle plug was collected with a 5-mm (millimeter) stainless 

steel biopsy punch from beneath the dorsal fin area in each of the three whole-body fish samples 35337–

35339. Using clean forceps, the skin from each plug was removed with a stainless steel scalpel and the 

remaining tissue was transferred to a pre-cleaned polyethylene cryovial. Once created, the muscle plug 

samples were given new USGS identification numbers 35341–35343. Each whole-body fish sample was 

minced with a titanium meat cleaver. These minced samples, muscle plug samples, and the two tissue 

powder samples were then lyophilized with a Virtis Genesis®

 35EL freeze dryer and percent moisture 

was determined as part of the lyophilization procedure. Once dried, each minced whole-body fish 

sample was further homogenized by hand-kneading in a sealed plastic bag. All dried samples were 

stored in glass vials in a desiccator.

Instrumental Analysis and Data Reporting

Mercury was determined with a direct mercury analyzer. With this method, a dried sample of 

approximately 31 to 69 mg (milligrams) was combusted in a stream of oxygen. All mercury in the 

sample was volatilized and trapped by amalgamation on a gold substrate and was thermally desorbed 

and quantitated by atomic absorption spectrophotometry (U.S. Environmental Protection Agency, 

2003). The entire sequence was conducted with a Milestone Direct Mercury Analyzer (DMA-80) 

equipped with an automated sample carousel. Triplicate determinations were conducted for the wholebody fish and tissue powder samples and the mean of the three analyses was reported. Because of the 

limited biomass, only one determination could be performed for each muscle plug sample. The 

concentrations of mercury measured in whole-body fish samples and fish muscle plugs were converted 

to wet weight for reporting. Concentrations of samples received as powders were reported “as received.” 

Based on historical measurements, residual moisture of homogenized, lyophilized, and desiccator-stored 

fish fillet tissue typically is 3 to 5 percent, but no attempt was made to apply a correction for residual 

moisture of individual dry samples because the mercury analyzer is calibrated with dried certified 

reference tissues having similar ranges of moisture content. The uncertainty of reported wet-weight 

concentrations, potentially because of moisture differences among the individual dried unknown 

samples and the certified reference samples used for the calibration, is expected to be considerably less 

than the overall method uncertainty (plus or minus 5 to 10 percent for mean concentrations at least three 

fold above the method quantitation limit). Furthermore, the uncertainty associated with moisture 

variation among dry sample determinations should be no greater than the uncertainty associated with 

moisture variation among fresh or frozen fish fillet sample analyses. 

Results and Discussion 

Percent moisture and mean concentrations of total mercury measured in whole-body fish and a 

muscle plug from each of those fish are presented in table 1. Percent moisture in whole-body fish 

ranged from 71.8 to 73.8 percent and averaged 73.0 percent, whereas moisture content of muscle tissue 

ranged from 75.1 to 79.4 percent. Mercury concentrations in whole-body fish ranged from 0.048 to 

0.061 μg/g (microgram per gram) wet weight and averaged 0.054 μg/g wet weight. The concentration of 

mercury in each fish muscle plug was about 30 percent greater than the corresponding whole-body 

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residue. These ranged from 0.061 to 0.082 μg/g wet weight and averaged 0.070 μg/g wet weight. All 

sample concentrations were well below the U.S. Environmental Protection Agency’s fish consumption 

advisory of 0.30 μg/g wet weight (U.S. Environmental Protection Agency, 2001). 

Percent moistures and concentrations (μg/g as received) of total mercury in submitted tissue 

powder samples are presented in table 2. Percent moistures were 5.4 and 5.2 percent. As mentioned 

earlier, mercury concentrations were not corrected for this residual moisture because the DMA-80 is 

calibrated using dried reference tissue powders with comparable residual moisture values. 

 

Table 1. Total mercury concentrations in whole-body fish and fish muscle plugs from the South Fork Humboldt River, Nevada, 2005. 

[USGS, U.S. Geological Survey; ID, identification; g, gram; mm, millimeter; n, number; μg/g, microgram per gram wet weight]

 Fish fork Fish total Mean total 

USGS ID Field ID Fish weight length length Percent mercury 

number number Sample type (g) (mm) (mm) moisture n (μg/g) 

35337 LCCSIF002 whole-body 70.4 175 184 73.5 3 0.048 

35338 LCCSIF003 whole-body 148. 232 239 73.8 3 0.061 

35339 LCCSIF004 whole-body 475. 338 351 71.8 3 0.053 

 

USGS ID Field ID Percent Total mercury 

number number Sample type moisture n (μg/g) 

35341 P130-LCCSIF002 muscle plug 77.3 1 0.061 

35342 P131-LCCSIF003 muscle plug 79.4 1 0.082 

 35343 P132-LCCSIF004 muscle plug 75.1 1 0.068 

Table 2. Total mercury concentrations in dry tissue powders submitted with wholebody fish samples, 2005. 

[USGS, U.S. Geological Survey; ID, identification; n, number; μg/g, microgram per gram as received] 

 

 Mean total 

USGS ID Field/lab ID Percent mercury 

number number moisture n (μg/g) 

35336 LCCSIF001 5.4 3 2.85 

35340 LCCSIF005 5.2 3 2.88 

Quality Control 

The samples were handled in one group, or block, through the instrumental analysis. Quality 

control included blanks, replicates, pre-combustion spikes, and tissue reference materials. During the 

instrumental run, additional quality control included independent calibration verification checks. 

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For the group or block of samples, two independent calibration verification samples [National 

Research Council Canada (NRCC) DOLT-2 and International Atomic Energy Agency (IAEA) 407] 

were analyzed at the beginning and end of the instrumental run to confirm the calibration status of the 

DMA-80 system; each measured calibration sample was within plus or minus 10 percent of the certified 

concentration. Five reference tissues were analyzed for mercury: NRCC DORM-2 (n=1), National 

Institute of Standards and Technology (NIST) RM50 [n=1 (one sample)], IAEA 407 (n=2), NRCC 

DOLT-2 (n=2), NIST 2976 (n=3); recoveries of mercury were within certified or recommended ranges. 

Method precision can be estimated from the percent relative standard deviation (RSD) from triplicate 

analysis of a sample. Percent RSDs from triplicate analyses of whole-body fish samples (n=3) and 

unspecified dry tissue powders (n=2) were less than or equal to 13 percent. Percent recovery of 

methylmercury hydroxide from pre-combustion tissue spikes (n=2) were 110 and 112 percent. Although 

all spike recoveries were above 100 percent, the mean recovery was well within quality-control protocol 

target limits (80 to 120 percent). Moreover, spike recoveries are not necessarily the best indicator of 

accuracy for the DMA-80 method because the instrumental response for liquids is sometimes slightly 

different than for solids. The blank equivalent concentration for total mercury (0.00003 μg/g dry weight) 

was less than the method detection limit. The instrument detection limit was 0.007 μg/g dry weight 

mercury. The method detection limit was 0.011 μg/g dry weight mercury, and the method quantitation 

limit was 0.038 μg/g dry weight. Overall, the quality control was within acceptable limits as specified 

by the USGS. 

References Cited 

U.S. Environmental Protection Agency, 2001, Water quality criterion for protection of human health—

Methylmercury: Washington, D.C., U.S. Environmental Protection Agency, Office of Water, EPA823-R-01-001, 269 p. 

U.S. Environmental Protection Agency, 2003, Draft update IVA of SW-846, 7000 series, Method 7473, 

Mercury in solids and solutions by thermal decomposition, amalgamation, and atomic absorption 

spectrophotometry: accessed July, 2005 at URL http://www.epa.gov/epaoswer/hazwaste/test/ 

up4a.htm#7_series. 

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For more information concerning the research described 

in this report, contact: 

U.S. Geological Survey 

Columbia Environmental Research Center 

4200 New Haven Road 

Columbia, MO 65201 

(573) 875–5399 

http://www.cerc.usgs.gov

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May and Brumbaugh—Determination of Total Mercury in Whole-Body Fish and Fish Muscle Plugs Collected ,—Open-File Report 2007-1059

from the South Fork of the Humboldt River, Nevada, September 2005