Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 1999
Publication Date: March 1, 2000
Interpretive Summary: Contamination of food and water by microorganisms from animal manures has become a recent concern. Non-point source contamination may result from pastured animals, wild animals or from manure spread on fields as fertilizer or waste. Point source contamination may include animal feed lots and housing facilities or manure storage areas. Current federal regulations do not address pathogens from animal manure, though the Clean Water Act (40 CFR 122) covers pollutants (mainly nutrients) from point sources under the National Pollutant Discharge Elimination System (NPDES) permit program, though regulation stops when manure is spread onto a field. Risks assessed here include the ability of potential pathogens, namely E. coli O157:H7 and coliforms, to travel through different soil textures. We also assessed whether the presence of manure binds pathogens at the soil surface or is a source of nutrients enhancing pathogen survival. We found that manure slightly enhanced survival of E. coli in soil, though high levels surviving in and leaching from soil without manure represented the same level of risk. E. coli O157:H7 could replicate in all of the tested non-sterile soils, was distributed evenly through the soil profile, and would continue to travel vertically if there was rainfall or irrigation. If soil pores do not clog, E. coli O157:H7 will continue to leach through the soil from between 25 to 134 days after application. Leaching of E. coli O157:H7 correlated with some nutrients, indicating that management through NPDES may be effective for pathogen control, though more investigation is needed. To maintain a safe environment and reduce risks, on-farm pathogen management may be necessary prior to spreading manure onto agricultural fields.
Technical Abstract: Application of animal manures to soil as crop fertilizers is an important means for recycling the nitrogen and phosphorus they contain. These animal manures also contain bacteria, including many types of pathogens. Pathogen levels depend upon the source animal, the animal's state of health, and how the manure was stored or treated before use. Rainfall may result in pathogen spread to soils by runoff from stored or unincorporated manure, or by leaching through the soil profile. Steady rainfall of 1.65cm hr-1 was applied to 10cm disturbed soil cores treated with manure and inoculated with E. coli O157:H7 B6914. B6914 in leachate exceeded inoculum levels hourly for 8 hours, as did levels of B6914 in soil after 24 hours, indicating a high rate of growth. Bacterial movement through 3 different soil types was then compared in disturbed (tilled) and undisturbed (no-till) soil cores using a less intense rainfall of 2.54cm daily for 1 week then at 3-4 day intervals for 2 more weeks. Total B6914 in leachate exceeded the inoculum in all cores except intact clay loam cores due to clogging and disturbed sandy loam cores due to low fertility. B6914 in leachate decreased sharply over time, though levels from sandy loam cores were more constant. B6914 in soil after 18 days was near the inoculum level in all cores, but lowest in the sandy loam. Presence of manure did not significantly increase B6914 survival in leachate or soil. Ammonia levels positively correlated with B6914 and total coliforms in leachate. We conclude that tillage practice, soil type and method of pathogen delivery may affect but will not prevent vertical E. coli O157:H7 and coliform transport in soil.