Since 1992, freight trains from distant cities such as New York have been making daily deliveries of two hundred tons of specially treated sewage sludge to the small town of Sierra Blanca, Texas, near the U.S.-Mexico border. On the outskirts of town, sludge from processed toilet and sewer waste is spread along more than one hundred thousand acres of farmland.

In virtually every U.S. state, specially treated sewage sludge is being applied to agricultural land. However, observers, including the residents of Sierra Blanca, are divided concerning the agricultural use of sewage sludge. Opponents of this technique argue that such sludge is laden with toxic ingredients including asbestos, dioxins, pathogens, petroleum, and heavy metals such as lead. According to writer Weston Kosova in Audubon magazine, “The blunt reality is there are dozens of potential toxins in sludge...