2. Natural sources modified by technology

Many products are naturally radioactive and only irradiate people if they are processed before use. Fertilizers, for example, are derived from natural minerals and irradiate the people who use them. Moreover, while irradiation by cosmic rays is inevitable, operating an airline exposes people to a level of irradiation that would not exist if transport were purely terrestrial. All these activities are sources of exposure to natural radiation brought about by the development of new technologies.