Every year waste treatment facilities in
The practice helps solve storage issues and produces revenue to support the treatment plants, but what else is being spread in that sludge?
As industry invents new materials and chemicals for modern products, many find their way to our skin and bloodstream and, subsequently, into our sinks and toilet bowls. More than 500 different organic chemicals have been identified in the biosolids used as fertilizer across
Federal law regulates remnant levels of heavy metals and pathogens in the biosolid fertilizer, but chemicals are not currently accounted for because it has been prohibitively expensive to even begin sorting out which ones might be ecologically unfriendly, says
In a recent study, Gunsch and colleagues from
The team describes their new testing method and some of its early findings in the
"Because we're finding many emerging contaminants in biosolids, we wanted to develop a method where you could check them quickly and efficiently and flag the most potentially dangerous ones for more complex measurements," said
An important benefit of fertilizing soil is replenishing nitrate levels, which are crucial to growing plants. One indicator of the soil's health is the rate at which native bacteria are breaking down those nitrates through a process called denitrification. If antimicrobials or other chemical agents are affecting the bacteria's ability to complete this process, the soil's quality is degraded.
The new screening technique involves growing a bacterium commonly found in soil that is important to the nitrogen cycle -- Paracoccus denitrificans -- in pure laboratory cultures. Researchers then add various amounts of the chemicals in question to determine the minimum amount that affects the denitrification process.
"We chose the nitrogen cycle as an indicator because we wanted to represent an environmental process that is critical to agriculture," Holzem said. "Typically you have to use a complex,
To test the new screening technique, Holzem and Gunsch worked with
"These chemicals are everywhere," said Gunsch. "Our society loves products that prevent microbial growth."
The results showed not only that the technique works, but that it is more sensitive than laborious and more expensive testing methods involving measurements of gene expression and cell viability.
While the screening process only looked at the effects of six antimicrobial agents on one indicator of environmental health -- the nitrogen cycle -- Gunsch and Holzem say the technique could be used to test a variety of compounds through many different ecological indicators.
"We hope that companies developing new chemicals might use this method to start looking at potential environmental threats before incorporating them into consumer products," said Gunsch.
Their work was supported in part by the National Science foundation grant CBET-0854167.
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