From Flush to Farm; October 2002; Scientific American Magazine; by Rebecca Renner; 2 Page(s)

Ten years ago the U.S. stopped dumping sewage sludge in the ocean because of concerns about polluting the marine ecosystem. Since that time, the dregs from our drains have been going to farmland-as fertilizer. This practice has been contentious from the onset. Advocates enthuse about the success of sludge recycling. Opponents cite health complaints from those living nearby. But in terms of the science, "we are doing something on a big scale, and we don't know enough about it," says Thomas A. Burke, a public health professor at Johns Hopkins University.

Treated sludge, also known as biosolids, makes good fertilizer because it is high in organic content and plant nutrients. But sludge also harbors low levels of metals, organic pollutants and disease-causing microbes, so the U.S. Environmental Protection Agency has regulated its use under Part 503, a 1993 regulation of the Clean Water Act. The rule divides treated sludge into two classes. Class A sludge contains no detectable pathogens and can be used anywhere. Class B sludge, which accounts for the bulk of the fertilizer, is treated to reduce pathogen levels to below certain thresholds. The EPA stipulates limited public access to sites where class B sludge has been applied.