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Sludge Application to Land Compared with a Pasture and a Hayfield: Reduction of Biological Health Hazard Over Time¹

ABSTRACT

Economic and environmental pressures favor the disposal of sewage sludge on agricultural land. In order to assess this hazard, this study investigated the occurrence and survival of primary and secondary bacterial pathogens, parasite eggs, and enteroviruses in sludge injected by machine into a fallow field, sludge spread on a grass plot (Poa spp. and Fescue spp.), a pasture grazed by cows (Bos taurus), and on soil taken from a control hayfield (dominated by Bromus spp.). It was assumed that the unsludged hayfield represented an acceptable level of "risk."

The sludged plots compared favorably with the control hayfield with respect to the occurrence and survival of nematode parasites, enteroviruses, and primary bacterial pathogens. Secondary bacterial pathogens persisted on all fields throughout the study, but levels declined more slowly on the sludged grass plot than the injected sludge field, the pasture, or the control hayfield. Despite the persistence of secondary pathogens (which are normally present on grazed fields), the health hazards to humans and animals were judged to be comparable to those on a hayfield and a pasture that had not been sludged.

Key Words: coliforms • Salmonella • Staphylococcus • parasites • viruses • health hazard • sludge

¹ Work supported through contract no. 80-9108 from Alberta Environment (Research Management Division) and a grant from the Alberta Environmental Research Trust.

² Research scientists, Kananaskis Centre for Environmental Research, Univ. of Calgary, Calgary, Alberta, Canada T2N 1N4.

Received for publication March 12, 1984.