The fate of Escherichia coli and E. coli O157 in cattle slurry after application to land.

The fate of both faecal Escherichia coli and E. coli O157 in slurry following application to arable and grass plots on a clay loam soil was studied. Slurry (5% dry matter) containing 5.3 x 10(4) ml(-1) E. coli and 30 E. coli O157 100 ml(-1) was spread in early March. Initially, almost all E. coli were retained in the upper layers of the soil. Escherichia coli numbers steadily declined to less than 1% of those applied by day 29, and E. coli O157 were only detected in the soil and on the grass for the first week after application. There was some transport of bacteria to deeper layers of the soil, but this was approximately 2% of the total; transport to drains over the same period was mainly associated with rainfall events and amounted to approximately 7% of applied E. coli. However, there were indications that periods of heavy rainfall could cause significant losses of E. coli by both leaching and run-off. Experimental studies showed that E. coli O157 on grass, which was subsequently ensiled in conditions allowing aerobic spoilage, could multiply to numbers exceeding 10(6) g(-1) in the silage.