Regarding longer-term hazards, a number of hazardous waste constituents are also carcinogenic, or cause non-cancer toxicity to different organs over long low level exposure periods, while many others have thresholds for toxicity below which exposure is expected to have no adverse effects. For HLW, the limescale for the radioactivity to decay to around the level of the original uranium ore is around 100 000 years whereas for LBLW, many of the isotopes have half-lives less than around 30 years. Some hazardous wastes (e.g. some organic chemicals) biodegrade and their hazards reduce over time. These wastes can thus be theoretically considered as having an infinite “half-life”.