Studies were conducted to determine: (a) the heavy metal concentrations in Halton Region agricultural soils; and (b) whether a 1984 estimate of at least 39 yr for practicing land application of sludge in the Region was valid. Soil samples were taken on a regular grid pattern from the agricultural area of the Region. In a very large proportion of the samples, heavy metal concentrations were less than the maximum permissible values for sludge application to land in Ontario and in most of the samples, they were less than or approximately equal to the mean values for uncontaminated soils in Ontario. In a small proportion of the samples, heavy metal concentrations exceeded the maximum permissible values for sludge application to land in Ontario. These samples were obtained mainly west of the Niagara Escarpment in the southwest corner of the Region and the offending metals were primarily Pb and Zn. High Pb and Zn concentrations in these soils were not related to sludge application but were naturally occurring and probably were derived from Pb and Zn sulfides in the soil parent material. It was concluded that sludge may be applied on a very large proportion of the agricultural land in Halton Region and that the 1984 estimate of at least 39 yr for continuing this practice was valid. Moreover, in view of recent reductions in annual sludge quantity for land application in the Region and in sludge Cd concentration, the 39-yr estimate was considered to be conservative. Key words: Heavy metals, cadmium, Halton Region, municipal sludge, land application
Risk assessment of Escherichia coli in bioaerosols generated following land application of farmyard slurry
