Sludge's dirty secret is that it may contain anything that goes down the drain—from Prozac flushed down toilets to motor oil hosed from factory floors. While sludge sold to consumers must be virtually pathogen free, sludge used on farms and industrial sites is permitted to contain low levels of human pathogens. A federal radiation task force recently warned that sludge might be contaminated with radioactive waste; in January, shipments of Canadian sludge with elevated radioactivity levels were turned back at the border. Food companies such as Del Monte and H.J. Heinz won't accept produce grown on sludge-treated land. The Netherlands and Switzerland effectively ban the use of sludge on farmland, and 37 states regulate it more strictly than the EPA.
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