There is concern that increased industrialization may be increasing the mineral content of river water. Ten years

Question:

There is concern that increased industrialization may be increasing the mineral content of river water. Ten years ago, the silicon content of the water in a certain river was 5 mg/L. Eighty-five water samples taken recently from the river have mean silicon content 5.6 mg/L and standard deviation 1.2 mg/L. Can you conclude that the silicon content of the water is greater today than it was 10 years ago?