Public water systems often add fluoride to drinking water because, in the proper amounts, fluoride improves dental health and prevents cavities. Too much fluoride, however, can cause fluorosis, which stains teeth. In 2015, the U.S. Public Health Service (PHS) revised its 1962 recommenda- tions for the amount of fluoride in public water systems. The 1962 recommendations depended on the average temperature for the region in question as shown here. because U.S. citizens are now getting fluoride from other sources, including toothpaste and mouthwash. The rec- ommended level balances the need for fluoride to im- prove dental health with the risk of developing fluorosis from too much fluoride. Examine the data in the table and answer the following questions: (a) Determine the percent change in optimum recom- mended fluoride concentration for a water system with annual average maximum daily temperatures of 17.8–21.4 °C. Hint: the percent change is given by 1962 Fluoride Recommendations final value – initial value Annual Average of Maximum Daily Air Temperatures (°C) Recommended Fluoride Maximum % change = x 100%. Concentration (mg/L) Allowable Fluoride initial value Concentration (b) Sodium fluoride (NaF) and sodium fluorosilicate (Na,SiF6) are commercially available in 100.0-lb bags. Calculate the mass in kg of fluoride in a 100.0-lb bag for each of these compounds. If the compounds cost about the same per 1000.0 lb, which compound would bc the better choice from an cconomic point of Lower Optimum Upper (mg/L) 10.0–12.0 0.9 1.2 1.7 2.4 12.1–14.6 0.8 1.1 1.5 2.2 14.7-17.7 0.8 1.0 1.3 2.0 17.8-21.4 0.7 0.9 1.2 1.8 view? (c) The National Institutes of Health (NIH) recommends a fluoride intake of 3.1 mg/day for adult females and 3.8 mg/day for adult males. If drinking water contains 0.7 mg/L, how much water should a person consume daily to meet the NIH recommendation for women? For men? 21.5-26.3 0.7 0.8 1.0 1.6 26.4-31.5 0.6 0.7 0.8 1.4 The new recommendation is simply for municipalities to fluoridate public water systems at a level of 0.7 mg/L. Notice that this level is at the lower end of previous rec- ommendations. The recommended level was lowered