The radioactive isotope tritium has found its way into half of more than 6,000 wells researchers examined world-wide. Even wells containing water more than 10,000 years old, termed "fossil water", showed contamination by tritium, overturning a long-held assumption that wells dug deep enough could avoid contamination with modern pollution. The study was published online in Nature Geoscience on April 25. PollutionOnline.com