Effects on lambs of ingestion of soil treated with sevage sludge

Abstract

Sewage sludge contains a range of essential and non-essential elements for livestock nutrition, many of which are toxic at elevated levels. Where sludge is applied to the surface of pasture regularly, contaminants principally heavy metals will accumulate in the surface layer (Davis et al 1988), and may represent a potential health hazard for grazing animals through the direct ingestion of contaminated soil much greater than that from plant uptake. Whilst it is known that soil ingestion can supplement mineral intake with benefits to grazing animals in some situations, the potentially toxic effects of ingesting soil from heavily sludged pastures are of principal concern (Stark 1988). Bearing in mind the strategic importance of grassland for sludge disposal, it must be demonstrated whether existing soil metals limits (DoE 1988) will adequately protect grazing animals. The principal objective of the trial was to study animal growth performance as well as mineral balance from a diet with elevated copper levels derived from a sludge treated soil. Lambs were used for their greater sensitivity to copper than cattle, and the length of the trial simulated the normal finishing period of five months for lambs on pasture.