(a) The EPA threshold for acceptable levels of lead ions in water is <15 ppb. What is the molarity of an aqueous solution with a concentration of 15 ppb?

(b) Concentrations of lead in the bloodstream are often quoted in units of μg/dL. Averaged over the entire country, the mean concentration of lead in the blood was measured to be 1.6 μg/dL in 2008. Express this concentration in ppb.