Literature Cited
(1) Marauart. J. R.. Dellow. G. B.. Freitas. E . R.. Anal. Chem.. 40, 163’3-7 (1968). (2) Kawahara, F. K., Enuzron Scc Technol , 3, 150-3 (1969). (3) Folmer, 0. F., Jr., Anal Chcm Acta, 60,37-46 (1972). ( 4 ) Stuckey, C. L., zhza , 10,47-56 (1972). (5) Mattson. J. $3.. Mark. H. B . Jr.. KolDack. R L.,Schutt, C. E.,Anal Chem., 42, 234 (1970). (6) Jeltes, R., den Tankelaar, W. A . M., Water Res, 6 , 271-8 (1972).
(7) Kawahara, F . K., J . Chromatogr. Sci., 10,629-36 (1972). (8) Williams, D. H., Ed. “Mass Spectrometry,” Vol. 1, The Chemical Society, Burlington House, London, 1971. (9) Cuthbert, J., Denney, E. J., Silk, C., Stratford, R., Farren, J.. Jones. T. L.. Poolev. D.. Webster. R. K.. Wells. F . H.. J . Phys. E , 5,698-704 (1972). (10) Dell’Acqua, R., Bush, B., Int J Enuiron Anal Chem , 3, 141-6 (1973).
Received for review Decemher31, 1973. Accepted October 9, 1974.
Mercury Levels in Lake Powell Bioamplification of Mercury in Man-Made Desert Reservoir Loren Potter,” David Kidd, and Donald Standiford The University of New Mexico, Albuquerque, N.M. 87131
Flameless atomic absorption analyses of samples from Lake Powell yield mean mercury levels in ppb of 0.01 in water, 30 in bottom sediments, 10 in shoreline substrates, 34 in plant leaves, 145 in plant debris, 28 in algae, 10 in crayfish, and 232 in. fish muscle. Trout were unique in having lower concentrations in muscle than in highly vascularized blood tissues. Concentrations increased with increased body weight and higher levels on the food chain. Muscle of some large fish over 2 kg whole body weight exceeded 500 ppb. Bioamplification of mercury up the food chain and association of mercury with organic matter are demonstrated. W
The vulnerability of freshwater habitats to mercury contamination was established by Swedish investigations ( I ) . Mercury levels exceeding the U.S. Food and Drug Administration “interim guideline” of 500 ppb for flesh have been found in fish from many North American locations. This level is a maxiimum, allowing an intake of two fish meals per week if the serving averages 150-200 grams. Levels above 500 ppb have been considered evidence for pollution, but these high levels have also been obtained for fish from habitats with no known pollution source (24 ) . This illustrates the difficulty of determining sources of mercury pollution--ii problem that becomes even more complex when we consider inputs from fossil fuel combustion. Lake Powell, a Cdorado River impoundment near Page, Ariz., is a new reservoir remote from major man-caused pollution sources and affords a unique opportunity to establish baseline mercury levels in a reservoir with concentrations resulting principally from the erosion of natural geologic deposits. The extent of bioamplification through the food chain in such a recent, relatively unpolluted lake is of interest. These baseline levels will be used to evaluate the impacts of rapid recreational development and future operation of large-scale coal-fired power generation facilities near the impoundment. Lake Powell, a Bureau of Reclamation storage and hydroelectric generation reservoir, was initially impounded in 1963 and reached a 1971 elevation of 1104.3 meters with a volume of 17,860.6 X 106 m3 (14 million acre ft). The lake has a potential storage capacity of 33,304.5 x 106 m3 (27 million acre ft), with a length of 300 km. Annual run-
off into the lake is about 14,800 X 106 m3 (12 million acre f t ) . The deeply dissected sandstones and shales of the canyons of the Colorado River system in southeastern Utah and northern Arizona produce a shoreline characterized by precipitous cliffs, sparse vegetation, and little soil development. Our purpose is to report baseline mercury levels in water, terrestrial substrates, bottom sediments, and various trophic levels; to provide concentration factors of mercury from one trophic level to the next; and to suggest the need for a clearer understanding of the mercury budget.
Analysis Procedure Water samples were preserved in glass or polyethylene containers with 3 ml/l. of 50% nitric acid added at the time of collection, and all samples were analyzed in less than two weeks. Samples were not filtered, but were analyzed after concentrating the mercury by the dithizone extraction method. Chau and Saitoh (5) reported losses of 35, 82, and 65% after one week if samples were not acidified. Since mercury species may be bound to suspended particulate matter, it is possible that our stated values for mercury are not valid for water alone, but reflect mercury concentration of the unfiltered water with the associated suspended materials. However, concentrations reported by us are low and do not indicate an undue bias. When sufficient material was available, sample sizes of 1 gram for organic material and 5 grams for mineral material were used, with from two to five replicates. When practical, materials were ground or blended to prepare homogeneous samples. Terrestrial soils and bottom sediment samples were analyzed in the form collected; biological materials, such as floating organic debris, aquatic organisms, and terrestrial plants, were analyzed as recovered from the frozen or air-dried condition. Tissue separation and homogenization were on fish still partially frozen. Portions of sediment and plant samples were weighed and saved for dry weight comparison. Concentrations of mercury for sediments, soils, and plant materials are expressed on an air-dry weight basis; crayfish and fish data are on a wet weight basis. In each case the material analyzed was in the condition or state in which it would be ingested or passed on through the food chain. Samples were analyzed using the flameless atomic absorption procedures outlined by Hatch and Ott (6) and Uthe et al. (7) as modified for use with a Perkin-Elmer Volume 9, Number
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Model 306 atomic absorption spectrophotometer equipped with a Perkin-Elmer mercury analyzer system. Mean percentage recoveries . and mean coefficients of variation (c.v.) for the types of materials analyzed were: water 92.2% (13.0); geological material 96.0% (7.1); plant material 99.8% (14.2); and fish 101.6% (9.81).
Mercury Levels of Water Mercury levels of unfiltered Lake Powell waters are low. We found mean levels of about 0.01 ppb ( a = 0.009 ppb, std dev = 0.001). These low levels are expected. Wershaw (8) concludes that mercury levels are 0.1 ppb or less in unpolluted fresh waters and reports USGS results of levels a t or below their 0.1 ppb detection limit for 34 of 73 samplings from the Colorado River. Our levels, averaging 0.01 ppb, are based on 12 water samples from nine widely scattered locations in Lake Powell. Samples were collected from the surface and at 4or 5-meter depths. Sample variation between locations and depths were expected on the basis of chance alone (0.95 probability level). Apparently there is little mercury even in the unfiltered water which contains suspended material. It is this water medium through which mercury must pass to become incorporated into mineral and organic matter sediments (9,
IO). Rocks, Soils, and Sediments Loose rock material collected from the Navajo Sandstone yielded levels less than 30 ppb, dry weight. Analysis of collections from unconsolidated sedimentary rock debris, low in organic material, gave mercury levels less than 30 ppb. Sand was particularly low in mercury content, with 76% of the 17 samples having levels below 5 ppb and only one sample having a level above 10 ppb. The USGS reports a wide range of mercury levels ( < l o to >6,000 ppb) in sedimentary rocks of this region (11). While most strata near the lake gave median levels of 100-260 ppb, the USGS found levels of
