But most of the 42,000 tons of sewage sludge spread across Minnesota farm fields last year is lower grade, Class B sludge, which typically contains measurable levels of pathogens. Jorja DuFresne, the biosolids coordinator with the Minnesota Pollution Control Agency, says Class B sludge is safe when properly applied. She points out that the state insists on certification and training for those who spread it.
In her 22 years working in the field, DuFresne says she has yet to come across a single documented case of a human health problem arising from the use of sludge in Minnesota.
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At the Met Council and NEFCO, meanwhile, officials maintain that the levels of fecal coliform (an indicator of the presence of pathogens) and heavy metals remain well below EPA allowable limits. There is one main reason for that, according to Met Council spokesman Tim O'Donnell: an 85 percent decrease in the amount of heavy metals found in metro waste water, thanks to "pre-treatment" of sewage by industrial users.
None of that impresses sludge critics like Laura Orlando. "If you say the only thing we have to be concerned about is these nine heavy metals, many municipalities are doing a good job. I contend, along with thousands of other people, that sewage sludge toxicity goes well beyond the nine heavy metals," Orlando says.
In fact, she asserts, there are "tens of thousands of chemicals" that enter the sewage treatment plant and cannot be mitigated by conventional treatment. Those chemicals--most of which are never identified through existing testing protocols--wind up on farm fields and, eventually, dinner plates.
Concerns over one particularly ubiquitous group of chemicals--called PBDEs--have led the Swiss government to impose an outright ban on the use of municipal sludge as fertilizer, and other countries are poised to follow suit. But, Orlando adds, PBDEs "aren't even on the EPA's radar."
"There's no alchemy here," Orlando says of the treatment of sludge. "No magic that can make all this stuff just disappear."