Harmless Titanium Dioxide Tracer (IMAGE) U.S. National Science Foundation Caption Scientists added a harmless titanium dioxide tracer to streams and rivers to track carbon flow. Credit Diana Karwan, Stroud Water Research Center Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.