Question

A water supply has been contaminated with
an unknown mixture of toxic metal solutions
leaking from a nearby factory. One way to treat
the problem is to precipitate the metals from the
water. Environmental chemists are considering
using sodium carbonate and sodium sulfate for
this purpose. Based on the solubility table, which
compound would you recommend?

Answer 1

According to the provided table of solubility the metals that form a precipitate with carbonate and sulfate are Ba and Pb but the only toxic one of these two metals will be Pb (lead)

Answer 2

Metals which are from precipitate with sulfate and carbonate are barium and Lead.

The only toxic of these metals is lead. Lead is heavy metal which is denser with most common materials.
 It contains major decay chain which has heavier elements. It is unreactive post-transition metal.