This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Dental
Plasma  fluoride  level expected in a  healthy, fasting, long-term resident of a community with a water fluoride level of 1 ppm is approximately? 
Select and explain. 
A. 0.01 ppm, B. 0.012 ppm, C. 0.015 ppm, D. 0.019 ppm
D: 0.019 ppm
Answer: D: 0.019 ppm 
Explanation: The  ionic  fluoride  is of  public health significance. It varies  according  to the concentration of fluoride in the drinking water.  Its  plasma  concentration  is approximately  twice  as  high  as  that associated with the blood cells. Since plasma fluoride  levels  are  not  homeostatically regulated, there is no normal physiologic concentration.  Plasma  fluoride  level expected in a  healthy, fasting, long-term resident of a community with a water fluoride level of 1 ppm is approximately 1 µM (0.019 ppm). There is evidence that plasma fluoride levels increase slightly with age.