Skip Links

USGS - science for a changing world

Data Series 309

Trace-Element Concentrations in Tissues of Aquatic Organisms from Rivers and Streams of the United States, 1992–1999

By Lawrence R. DeWeese, Verlin C. Stephens, Terry M. Short, and Neil M. Dubrovsky


Home
Abstract.html
Introduction
Methods
Results
Acknowledgments
References Cited
Conversion Factors and Notes

Methods

NAWQA was designed to be a nationally uniform and consistent program, and therefore methods were prescribed to be followed by all study units. Due to regional variability around the United States, however, some methods had to be modified for local conditions. The methods used in the tissue-sampling program are discussed in the sections that follow.

Site Selection

A total of 824 sites were selected to be sampled for aquatic tissue. Typically, 20 to 30 sites were selected within each study unit. These study-unit sites included four to eight periodic surface- water monitoring sites and multiple synoptic sites. The periodic monitoring sites were selected to represent large stream basins (integrator sites) or principal land uses (indicator sites) (Gilliom and others, 1995). The most common land uses monitored were agriculture, cropland, pasture, urban, commercial/industrial, residential, forest, rangeland, point source, and mining. Usually one or two monitoring sites within each study unit were selected to represent natural background environments where concentrations of trace elements might be expected to represent background (reference) conditions with minimal anthropogenic effects; typically, these reference sites were located in forest or rangeland land uses. Synoptic sites were selected to fill in geographic gaps between monitoring sites within a study unit, or to represent less prevalent land uses.

Species Targeted for Collection

From 1993 to 1995 whole bodies of caddisfly larvae (Hydropsyche spp.) and soft bodies of asiatic clams (Corbicula fluminea) were targeted as the two best indicators of trace elements in streams and rivers (Crawford and Luoma, 1993). From 1996 to 1999 liver tissue taken from adult common carp (Cyprinus carpio) and white sucker (Catostomus commersonii) served as the primary targeted tissue because these two species are more widely distributed and could be obtained at a larger number of collection sites, thereby better serving the goal of achieving a nationally consistent data base. Dace (Cyprinidae) and sculpin (Cottidae) were targeted in the Pacific Northwest region because common carp and white sucker were not consistently available in this region. Largemouth bass (Micropterus salmoides), smallmouth bass (Micropterus dolomieu), rock bass (Ambloplites rupestris), and asiatic clams (Corbicula spp.) were collected in the Southeast and at scattered sites elsewhere, where they are common. In extreme cases where fish and invertebrates were not available, aquatic plants were collected for the trace-element analysis. Collection sites for fish and invertebrate species are shown in figures 2 and 3, respectively. Although not discussed in this report, samples of streambed sediment were collected along with the tissue samples and were analyzed for the same suite of trace elements.

Figure 2. Locations of fish-tissue collection sites, 1993-1999.

Figure 3. Locations of invertebrate-tissue collection sites, 1993-1999.

Sample Collection and Compositing Methods

Samples were collected, processed, preserved, and transported according to the recommendations of Crawford and Luoma (1993). For quality assurance purposes, two or three samples of the same species were collected at 1 or more sites in each study unit to provide replication at approximately 10 percent of the sites.

Fish were collected using various types of electro fishing gear or nets. Asiatic clams were collected from the stream bottom either by hand-picking or using a clam rake.  Caddisfly larvae and other aquatic insects were collected using a D-frame or similar type of kick-net sampler. Immediately following collection, all invertebrate organisms, such as clams and aquatic insects, were stored overnight in native water to evacuate gut contents and then were immediately frozen.

Composite samples were taken for all tissue types. For fish liver samples, composites consisted of liver tissue from five to eight individuals of a given species.  At a few stations, extracting liver samples from small-sized fish species was not practical, and a whole fish composite from 10 to 20 individuals was collected.  The number of asiatic clams collected for a single composite sample typically ranged from 20 to 30 individuals. The number of caddisfly larvae composing a single composite sample generally ranged from 40 to 60 individuals.

Multiple samples were collected at some sites at time scales varying from hourly to annually.  Two samples were collected at 122 sites, three samples were collected at 40 sites, four samples at 8 sites, five samples at 3 sites, and six samples at 1 site.  Multiple samples at a site commonly consisted of different organisms or different tissue types, but in other cases the same organism and tissue type were collected. The data presented here also include the results of a special mercury synoptic study done in the NAWQA Red River of the North study unit (REDN). For this study, 221 samples of channel catfish and carp were collected.  Information regarding this special study is discussed in detail by Goldstein and others (1996). 

Chemical Analysis

Trace-element concentrations were determined in tissues at the USGS National Water Quality Laboratory using the methods described in Hoffman (1996).  A low temperature (85 degrees Celsius) nitric acid digestion, followed by the addition of hydrogen peroxide (30-percent solution), was used to decompose the biological material.  The digested solutions were evaporated to incipient dryness, reconstituted with 5 percent nitric acid, and filtered.  After filtration, the solutions were diluted to a known volume and analyzed by inductively coupled plasma–mass spectrometry (ICP–MS), inductively coupled plasma-atomic emission spectrometry (ICP–AES), and cold vapor-atomic absorption spectrophotometry.  Many of the trace elements were determined by both ICP–MS and ICP–AES.  Minimum reporting levels for the trace-element concentrations were the following: mercury, 0.005 μg/g (microgram per gram dry weight); tin, beryllium, lead, nickel and uranium, 0.01 μg/g; iron, 0.13 μg/g; boron, 0.15 μg/g; cadmium, 0.03 μg/g; cobalt and molybdenum, 0.045 μg/g; barium, manganese, strontium, arsenic and selenium, 0.05 μg/g; silver, 0.10 μg/g; iron, 0.13 μg/g; chromium, 0.165 μg/g; and copper and  zinc, 0.025 μg/g. Samples spiked with known concentrations of trace elements were used as a quality-control method to evaluate the efficacy of the sample extraction and processing technique; recoveries from spiked samples ranged from 92  to 110 percent. Percent moisture in the raw tissue sample also was measured, so dry weight concentrations reported here can be recalculated back to wet weight concentrations.



Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: https://pubs.usgs.gov/ds/309/index.htm
Page Contact Information: Contact USGS
Page Last Modified: Wednesday, 05-Dec-2007 14:48:39 EDT