This rarely seen metal is most typically associated with nuclear pollution. Finding the strontium-90 isotope in the atmosphere around your neighborhood is bad news indeed and should be cause for immediate plans to relocate to your mother-in-law's for a while. But don't worry, that should only happen if you live near a malfunctioning nuclear power plant.
Strontium's other isotopes are considerably less harmful. In fact, one big use of it goes into toothpaste because it coats teeth in a microscopic film that protects against cavities. The piece here would be enough to seal a city's worth of its denizen's teeth. We really don't recommend chewing on it though.