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<br />. <br /> <br />of Des Moines in the 50-80 mg/t range; this was in contrast to <br />the spring and summer chloride levels which were below 20 mg/t <br />at both sampling points." <br />Other studies on chloride levels of major rivers have shown <br />similar results. Hutchinson (1967) analyzed seven major rivers <br />in Maine for sodium and chloride levels over the period 1965-67. <br />These ions were generally "1-2 mg/t at the headwaters and <br />increased to as high as 15-18 mg/t at the mouths of the respec- <br />tive rivers." Highest levels of sodium and chloride were shown <br />in the southern section of the state where highway miles were <br />greatest. <br />Special additives present within much of the highway salts <br />sold today may create pollutional problems even more severe than <br />caused by chloride salts. Ferric ferrocyanide and sodium ferro- <br />cyanide are commonly used to minimize the caking of salt stocks. <br />This sodium form is quite soluble in water, and will generate <br />cyanide in the presence of sunlight (Hanes, et al., 1970). <br />Tests showed that "15.5 mg/t of the sodium salt can produce 3.8 <br />mg/~ cyanide after 30 minutes." The maximum levels of cyanide <br />allowed in public water supplies range from 0.2 to 0.1 mg/~ <br />(USPHS. 1962). <br />Other special additives to highway salts have been chromate <br />and nutritious phosphate, used to inhibit corrosion (Hanes, et <br />al., 1970). As with cyanide, chromate is highly toxic, and <br />limits permitted in drinking and other water are in the same low <br />range. A study in the St. Paul-Minneapolis area during the <br /> <br />, <br /> <br />19 <br />