CHATTANOOGA, Tenn. (AP) - A University of Tennessee at Chattanooga professor says researchers need to keep an eye on the amount of medicines that make it into the Tennessee River. Professor of biological and environmental sciences Sean Richards has spent years analyzing samples from the Tennessee River between Chattanooga and Knoxville. He told the Chattanooga Times Free Press (http://bit.ly/1qvR2aX) that he and a team of researchers found trace amounts of 13 different drugs in 160 samples taken from the river. He says concentration levels will rise as the population increases. Richards says he tested for 14 active ingredients in various medicines that people take. He says although the concentrations were low, they were pervasive. Although the levels he found aren't harmful to humans, he said it's unclear whether they are harmful to the environment.