Tuesday, November 27, 2007

Manure Happens

Have you ever wondered how our produce becomes contaminated with E. coli O157:H7 and Salmonella ?

According to USDA, a typical cattle feedlot, which contains approximately 1,000 head of cattle, produces up to 280 tons of manure per week. And the last time anyone checked (about 10 years ago), manure samples from 63 of 100 feedlots contained E. coli O157:H7.

Until now, runoff from cattle feedlots has been stored in large ponds and then either processed for disposal or used as irrigation water. But USDA researchers have come up with a “new and improved” system. They propose to collect runoff in a temporary “basin” at the bottom of each feedlot. After allowing several minutes for the “solids” to settle to the bottom of the basin, the liquid will be spread (using a series of pipes) over an adjacent grassy field. Each fall, the accumulated solids will be removed from the basin and used to fertilize nearby cropland.

USDA claims that this new system is more environmentally friendly and reduces the risk of groundwater becoming contaminated with nutrient rich material from the old-style runoff storage ponds. But the agency is silent on the risk of contaminating cropland with pathogens.

Pathogens such as E. coli O157:H7, Salmonella, and Listeria monocytogenes can survive for several weeks in manure and in soil that has been fertilized with manure. Using untreated runoff water for irrigation, and uncomposted manure to fertilize cropland, risks spreading these pathogens through an entire agricultural area. I have to ask myself why USDA didn’t mention the ramifications of this important risk factor in its report.

We have reached our present disturbing level of produce contamination in part because no one thought through the risks involved in juxtaposing cattle feedlots and irrigated cropland. Before we implement a significant change to an important (and distasteful) aspect of feedlot management, we must be sure that we won’t be exchanging one problem for an even greater one.

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