Don't get too excited/worried--yet. The study found a correlation between Strontium 90 levels in baby teeth and cancer in later life.
As a statistician I have to remind you that correlation does
not imply causality. In this case, it could be that babies have genetic variability in their use of strontium in teeth, and this gene is also related to cancer risk. Or, and the sort of complex correlation that statisticians trace down all the time, smoking mothers may have been more likely to bottle feed babies, these babies are more likely to smoke in later life because their mothers did, and so on.
Notice that this possible scenario is a causal chain which has nothing to do with Sr90.
So where do you look for direct information on cancer rates
caused by Strontium 90 and other isotopes? Around the Windscale facility in England, Mayak (
http://en.wikipedia.org/wiki/Mayak) in Russia, and Chernobyl in the Ukraine, and in areas where food grown in the immediate areas was consumed. So far such studies do show a risk from Sr90, but a lot smaller one than this study, and original risk estimates postulated. (And just to be fair and balanced, cancer rates from Iodine-131, which gets concentrated in the thyroid, were worse than originally expected.)