Strontium is a metallic element with the chemical symbol Sr, chemically similar to calcium and therefore able to substitute for it in bone. Its food-safety relevance centres on the radioactive isotope strontium-90, a fission product that can contaminate milk, vegetables, and other foods after nuclear releases and accumulates in bone with long-term health consequences. Monitoring programmes test foods for strontium-90 in affected regions, and calcium-rich diets can reduce its uptake. The stable, naturally occurring isotopes are not a concern at normal dietary levels.