The current U.S. recommended buffer zone between cattle feedlots and vegetables may be too narrow, say scientists writing in the journal Applied and Environmental Microbiology.
“The high percentages of leafy greens contaminated with E. coli suggest great risk for planting fresh produce 180 m (590 feet) or less from a feedlot,” the investigators write. That suggests that current buffer zone guidelines of 120 metres (400 feet) from a feedlot may be inadequate.
A news release on the study says investigators sampled leafy greens growing in nine plots; three each at 60, 120, and 180 metres downwind from a cattle feedlot over a two-year period. The rate of contamination with the pathogenic E. coli O157:H7 bacteria declined with distance from an average of 3.5 per cent of samples per plot at 60 metres to 1.8 per cent at 180 metres.
This is the first comprehensive and long-term study of its kind, says first author Elaine D. Berry, of the U.S. Department of Agriculture, Agricultural Research Service, U.S. Meat Animal Research Center, in Clay Center, Nebraska.
A variety of conditions can affect the level of contamination, says Berry. For example, following a period of high cattle-management activity when the feedlot was dry and dusty, including removal of around 300 head of cattle for shipping, the rate of total non-pathogenic E. coli-contaminated samples per plot at 180 metres shot up to 92.2 per cent.
Conversely, total E. coli-positive leafy green samples were notably lower on one August sample date than on any other date, a finding the investigators attribute to cleaning and removal of feedlot surface manure from the nearby pens a few weeks earlier.