Long-term persistence and leaching of Escherichia coli in temperate maritime soils

Abstract

Enteropathogen contamination of groundwater, including potable water sources, is a global concern. The spreading on land of animal slurries and manures, which can contain a broad range of pathogenic microorganisms, is considered a major contributor to this contamination. Some of the pathogenic microorganisms applied to soil have been observed to leach through the soil into groundwater, which poses a risk to public health. There is a critical need, therefore, for characterization of pathogen movement through the vadose zone for assessment of the risk to groundwater quality due to agricultural activities. A lysimeter experiment was performed to investigate the effect of soil type and condition on the fate and transport of potential bacterial pathogens, using Escherichia coli as a marker, in four Irish soils (n = 9). Cattle slurry (34 tonnes per ha) was spread on intact soil monoliths (depth, 1 m; diameter, 0.6 m) in the spring and summer. No effect of treatment or the initial soil moisture on the E. coli that leached from the soil was observed. Leaching of E. coli was observed predominantly from one soil type (average, 1.11 +/- 0.77 CFU ml(-1)), a poorly drained Luvic Stagnosol, under natural rainfall conditions, and preferential flow was an important transport mechanism. E. coli was found to have persisted in control soils for more than 9 years, indicating that autochthonous E. coli populations are capable of becoming naturalized in the low-temperature environments of temperate maritime soils and that they can move through soil. This may compromise the use of E. coli as an indicator of fecal pollution of waters in these regions.

FIG. 1.

Sampling days, rainfall, and average cumulative amounts of leachate (n = 9) for the 4 soils during the experimental period.

FIG. 2.

Average (n = 3) total E. coli loads leached for the first 45 kg of leachate after application to soil by soil type (and treatment). Spr. Spring; Sum, summer.

FIG. 3.

E. coli loads leached for the 3 replicates for each RA treatment (C, control; Spr, treated in the spring; Sum, treated in the summer) and daily rainfall over the experimental period. The arrows indicate slurry application dates.

FIG. 4.

Average amounts of E. coli leached per ml of leachate from the control lysimeters (n = 3) for each soil type. The error bars indicate standard deviations.

FIG. 5.

Amounts of E. coli leached from the 3 replicates for each EL treatment (C, control; Spr, treated in the spring; Sum, treated in the summer) and daily rainfall over the experimental period. The arrows indicate slurry application dates.