MODEL RELEASED. Plant research with radioactive tracers. Researcher noting lysimeter results for plants that are being studied as part of an experiment on their uptake of tritium. Tritium is a naturally occurring radioactive isotope of hydrogen. It can be used as a radioactive tracer in plant experiments, but it is also a pollutant produced by nuclear power stations and nuclear research centres. Lysimeters are used to measure the amount of water evaporated and transpired by plants. This work is being carried out by the UK's Health Protection Agency.