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<br />. <br /> <br />o <br />~ <br />N <br />CJ1 <br /> <br />. <br /> <br />. <br /> <br />OTHER WATER QUALITY ASPECTS (Continued) <br /> <br />Radioactive pollution from industrial wastewater effluents, i.e., <br />uranium mills, was, prior to 1960, the major source of radioactive <br />pollution in the basin. The majority of the mills have been closed down <br />but a significant portion of the increase of radioactivity originates <br />from the abandoned tailings piles. <br /> <br />Radioactivity does impair the water for beneficial use when concen- <br />trations exceed certain limits. For example, the National Interim <br />Primary Drinking Water Regulations stipulate mandatory limits of 8 <br />picocuries/l for Sr-90 or 5 picocuries/l for combined Ra-226 and <br />Ra-228 in community water systems. Maximum contamination levels such as <br />these are derived on the basis that an individual ingesting two liters <br />of water daily will not receive an annual dosage to the body or any <br />internal organ of more than 4 mil lirems . Moreover, if two or more <br />radionuclides are present in the water supply, the sum of their dose <br />equivalent must not exceed the 4 millirem per year limit. <br /> <br />9. Mercury <br /> <br />A report by ~he Lake Powell Research Project on mercu\%,ublished <br />in 1973 and reprinted in 1975 gives the following information. <br /> <br />Samples analyzed by the flame less atomic absorption method showed <br />that mercury levels in mean parts per billion (mg/l) were .01 (.00001) <br />for the lake water, 30 (.030) in bottom sediments, 10 (.010) in shore- <br />line substrates, 145 (.145) in plant debris, 34 (.034) in plant leaves, <br />28 (.028) in algae, 232 (.232) in fish muscle and 10 (.010) in crayfish. <br />The concentrations were based upon a wet-weight condition for the <br />animals and a dry-weight basis for the rest of the samples. It was <br />found that the mercury content was higher in the sediments with the <br />higher organic content and that the lake transported plant debris had <br />higher contents than the shoreline plants. In the rainbow and brown <br />trouts, bloody tissues had higher mercury levels than the muscles while <br />in the six other .pecies analyzed the levels of bloody tissues heart, <br />kidney, liver, etc., were lower than the muscles. Larger fish of a <br />given species and fish of higher trophic levels have higher mercury <br />concentrations, with the muscle of some large walleye and largemouth <br />bass exceeding the 500 ppb. (.50 mg/l) guideline of the U.S. Food and <br />Drug Administration. <br /> <br />An estimated mercury budget suggested that due to the restriction <br />of flow by the impoundment, the mercury could be accumulative. <br /> <br />10. Sediment <br /> <br />Prior to construction of the storage units of the Colorado River <br />Storage Project, most of the larger tributaries and the main stem of the <br />Colorado River carried large loads of sediment, particularly in their <br />middle and lower reaches. <br /> <br />106 <br />