Animal and human health is unlikely to be at risk when generations of sheep graze bauxite residue (Alkaloam®)-amended pastures

Bauxite residue (Alkaloam®) applied to pasture has been shown significantly to improve pasture production on sub-fertile soil, such as those found in south-west Western Australia, because it increases soil pH. There are concerns that animals grazing Alkaloam-amended pasture may suffer ill health through heavy metal accumulation in tissues, and that this effect could be amplified over generations. There are additional concerns that eating exposed animals, or direct exposure to Alkaloam, may be detrimental to human health. Although some literature exists there are no studies that address these issues when the application of Alkaloam occurred several years (20) before grazing. This investigation examined the heavy metal and trace element accumulation in the tissues of Dorper lambs (1 year old) and their dams, Dorper ewes (4–5 years old) grazing Alkaloam-amended pasture. The experiment was conducted on two sites grazed in the Peel region of Western Australia: one site in Coolup, the Control site (Site C), that had had no application of Alkaloam and one site in Wagerup, the Treatment site (Site T), that had had 20 tonnes per hectare of Alkaloam applied in 1993. Both sites had uniform soil and pasture type during the growing season. Samples of soil and pasture were collected at each site. Differences in trace element concentrations, pH and conductivity between sites were determined. Ten ewes and 10 lambs were randomly selected at each site, removed and killed on the same day for gross examination of the kidney, liver and lung tissue. Samples of the tissues were collected for histopathological examination and chemical analysis to determine concentrations of trace elements. Depending on the concentration of trace elements in each sample, a logistical regression with binomial regression or an ANOVA was performed to determine differences in concentrations between ages, sites and any interactions between age and site. Sheep from Site T had significantly higher concentrations of copper, manganese and molybdenum, whereas sheep from Site C had significantly higher concentrations of cobalt, iron, lead, nickel, selenium, strontium and zinc in tissues. Ewes had significantly higher concentrations of barium, cadmium, cobalt, iron and strontium whereas lambs had significantly higher concentrations of copper, manganese and molybdenum in tissues. Ewes had higher concentrations of cadmium in the kidney compared with lambs, and ewes from Site C had significantly higher concentrations than ewes from Site T. Ewes and lambs from Site C had significantly higher concentrations of selenium in the liver compared with ewes and lambs from Site T. Concentrations of heavy metals (As, Hg, Pb, Th and U) were low in tissues of all sheep. The results show that whereas there were different elemental tissue concentrations between sites and between ages of sheep, there were no detrimental trace element imbalances or accumulation of heavy metals that would cause ill health in any of the sheep that could be associated with the application of Alkaloam to pasture. It is unlikely that humans will suffer any ill effects as a consequence of eating exposed animals. This result supports the premise that bauxite residue can be safely applied to pasture to significantly improve pasture and animal production where animals graze pasture growing on sub-fertile soil.