Sewage sludge is the mucky residue of municipal wastewater treatment operations, consisting largely of human feces. Repackaged as “biosolids,” sludge is sold or given away to farmers and homeowners for use as a nutrient-rich fertilizer.

But when used to grow food, our turds may bite back: sludge can contain heavy metals, pharmaceuticals, toxic chemicals, disease-causing bacteria (including e. coli and salmonella), viruses (hepatitis and polio), and parasites that can contaminate soil and potentially food crops. More than 330 synthetic chemical contaminants that have been detected in sludge are known or suspected toxins.

There has been little study of the health consequences of sludge use in farming. The Cornell University Wastewater Management Institute found just one published research review of illnesses in communities near sludge-applied land. This 2002 paper concluded that reports of “illnesses and even death” near farmland that used sludge suggested chronic and acute risks from exposure to contaminants in sludge. The researchers concluded that risks from sludge “suggests that [its] use should be eliminated.”

Fifteen years ago, Toxic Sludge is Good for You, the seminal book on the public relations industry, outlined in detail the birth of the sludge industry, exposing how the EPA funded an industry front-group to re-brand sludge as “biosolids” and promote its use as fertilizer (you can download the full chapter on sludge free of charge). Using taxpayer money, EPA concluded that sludge desperately needed an image-makeover to overcome the “widely held perception” that it is “malodorous, disease causing or otherwise repulsive.”

Convinced perhaps that their shit didn’t stink, EPA dismissed concerns about odors from sludge use as “irrational.”  The agency mused, “It is difficult to say to what extent odors emanating from sludge may be imagined.”

Today, sludge promoters are at it again and farmland isn’t the only sludge hazard. Some cities and towns offer fertilizer giveaways to home gardeners. In San Francisco, public interest groups led by the Center for Food Safety recently petitioned the city to end its “composted biosolids” giveaway program, citing potential health hazards.