The largest controlled isotopic tracer test that I’ve ever heard of is underway out in Arizona, in the huge “Biosphere 2” greenhouses. They’re simulating a drought in the rainforest section and comparing the carbon flux under normal and dry conditions through the use of 13C-labeled carbon dioxide. A few weeks ago the sealed system (under normal watering conditions) got a pulse of the labeled gas, and samples have been taken to quantify its uptake in the soil and all the plant species.
Now the irrigation in the rainforest area has been shut off for six weeks, and at the end of the drought another pulse of labeled CO2 will go in. Comparison of the two labeling experiments should give a unique view of how such ecosystems handle stress and what the differences in carbon flux might be – people have tried such experiments with semi-enclosed conditions in the wild, but as I understand it those results are not definitive. There’s no other place to do such an experiment under controlled conditions, and this seems like exactly the sort of experiment that the facility is suited for.
Isotopic labeling of this sort will be familiar to many chemists and biologists. It’s a mainstay of mechanistic experiments in both fields, and it’s a technique that has only increased in power and importance as mass spectrometry equipment has improved. One thing mass spec has done is shift some work away from radioactive isotopes to “cold” ones, which also allows for some very ingenious molecular-weight-bar-coding setups as well. The very first isotopic label/tracer experiments, though, were done by George de Hevesy, who later won the chemistry Nobel for the work (technically the 1943 prize awarded in 1944, because 1943 itself was actually a “no award” year for the chemistry prize, strangely). The technique was a revelation; the idea that you could track actual specific sources of matter through both in vitro chemical reactions and living organisms had been only a fantasy.
de Hevesy himself noted this in his 1934 paper on his personal ingestion of deuterated water (a gift from Harold Urey and a very exotic substance indeed in 1934). Having tea one day with Henry Moseley while he worked at Manchester (1910-1913), the two of them speculated about tracking the water in the tea through its journey through the body, and de Hevesy was glad both to reduce the experiment to practice and to memorialize his old colleague. Moseley had volunteered in WWI, despite pleas not to, and died at Gallipoli in a tremendous loss to science – of course, the losses to the human race in general as a result of that war are too numerous to count, and it’s better not to even start totaling them up. de Hevesy himself was drafted into the Austro-Hungarian army, bodies from whose campaign in the Alps have been recently re-emerging as the glaciers retreat. de Hevesy could have been one of them, but he fortunately ended up doing technical work in a copper factory.
Another de Hevesy/Manchester story, which I hope is true, is that one of his very first practical experiments with radioactive tracers was to prove that his landlady there was recycling uneaten roast beef from her tenants’ plates back into midweek hash. He was also the guy who dissolved von Laue and Franck’s gold Nobel medals in aqua regia at the Bohr Institute to hide them during the German occupation of Denmark during the next war, the one that World War I and its aftermath opened the door for. de Hevesy himself (who was Jewish) made it over to Sweden in 1943, and after the war returned to his old lab and found the bottle of acid sitting on the same shelf where he’d left it. Famously, the gold was then precipitated out and the medals recast. A man to reckon with!