Aug 21, 2003 — The more people inhabit the earth - the more sewage there is. Something has to be done with it. Before chemical fertilizers were invented, farmers used human manure to improve their crops. Some still do. About three million dry tons of treated sewage - called sludge - fertilize sod, pasture land and even food crops every year in the United States. The Great Lakes Radio Consortium's Amy Tardif looks at what the practice may be doing to the environment.