Ontario’s nuclear plants are the country’s largest source of dangerous tritium emissions. This radioactive isotope is produced — and released to the atmosphere — constantly by CANDU nuclear reactors. Once tritium is inside us, because we breathe it in, absorb it through skin or consume contaminated food or water, it release radioactivity in our bodies. Tritium is a carcinogen (causes cancer), teratogen (causes deformations of the embryo during pregnancy) and mutagen (causes mutations to DNA). Even very low rates of tritium exposure can lead to cancer, leukemia, and birth defects.