Overpowering manure. (Livestock Issues).

U.S. Department of Agriculture (USDA) scientists have lab-tested a cheap method for killing pathogenic bacteria in dairy cattle manure. If the technique passes upcoming field tests, it could help address growing concerns about the spread of disease by animal manure, and could possibly someday be used with other nondairy manures as well.

High concentrations of cattle urine can kill many bacteria in manure. Ammonia once got credit for the bactericidal effect, but research published in the 1 April 2000 issue of Environmental Science & Technology by a team under USDA research microbiologist James Russell indicates that carbonate ions released during enzymatic degradation of urea (a natural product of protein metabolism found in urine) are responsible. Russell says carbonate ions react with magnesium, an element essential to bacterial survival, forming magnesium carbonate and depriving the pathogens of magnesium.

To increase carbonate levels, Russell created the mild (pH 8.5) alkaline conditions necessary for carbonate to react with magnesium in dairy cow manure, then added sodium carbonate, a cheap and readily available chemical. Within 5 days, 4 grams of sodium carbonate per kilogram of manure reduced counts of Escherichia coli O157:H7 from several million per gram to less than 10--below the detection limit of their equipment. Russell found that sodium carbonate also kills many other human pathogens, including Salmonella typhimurium, Staphylococcus aureus, and Enterococcus faecalis.

The need for decontamination of manure is growing. E. coli O157:H7 is a deadly, hemorrhagic variant of the common bacterium that killed six people in Walkerton, Ontario, in 2000 when the municipal water supply was contaminated by farm manure runoff. A 1996 survey by the U.S. Environmental Protection Agency found E. coli bacteria in 40% of rural wells (however, most of that E. coli is not the O157:H7 variety, and not all E. coli comes from animal manure).

Dairy cattle alone produce more than 100 billion kilograms of manure per year. The increasing concentration of livestock operations, where thousands of animals produce large amounts of waste that are often spread at high concentrations on nearby farmland, is raising concerns about odor, overfertilization, and pathogens. Scientists now realize that E. coli can move rapidly through soil, a medium that was once thought to immobilize the bacteria. Researchers have found found that E. coli can percolate down through the soil and eventually reached groundwater, says Russell.

Mark Sobsey, a professor of environmental microbiology at the University of North Carolina at Chapel Hill, has studied contamination by animal wastes. In a paper delivered at the 3-5 October 2001 international symposium "Addressing Animal Production and Environmental Issues," held in Research Triangle Park, North Carolina, Sobsey wrote that millions or billions of human pathogens may live in 1 gram of fresh feces. "Therefore," he wrote, "the pathogens in animal manure and other wastes pose potential risks to human and animal health both on and off animal agriculture production facilities if the wastes are not adequately treated and contained."

Russell calculates that the carbonate treatment would cost $10 per cow per year. He expects that it might first be adopted in city watersheds or areas such as western New York State, where cow manure fertilizes vegetables.

Although human illnesses are seldom blamed on manureborne pathogens, Russell says the number of hidden cases could be substantial. "It's known that the vast majority of [foodborne illnesses] are not reported to epidemiologists; people just think they got a case of stomach flu," he says. "Whether or not the same pertains to water supplies, I don't know. There are probably cases where people get diarrhea and don't know the source at all. In some cases, [contaminated] water is probably the source."