Accumulation of potentially toxic metals in the liver tissue of sheep grazed on sewage sludge-treated pastures

Abstract

2005). Accumulation of potentially toxic metals in the liver tissue of sheep grazed on sewage sludge-treated pastures. AbstractConcentrations of potentially toxic metals ( PTMs) in the livers of pregnant, mature ewes and their 110 day foetuses, and in 6-month old lambs born to other ewes, were determined. The animals had been reared on pastures fertilized for 5 years with either sewage sludge (treated; T) or conventional inorganic fertilizer (control; C). The effects of treatment on patterns of accumulation of PTMs differed with stage of development and with individual PTM. In the liver of lambs, concentrations of Pb were elevated in T compared with C liver ( P < 0·01), while Cu and Zn were lower ( P < 0·001) in T than C liver. By contrast, in ewe liver, Cu concentrations were lower in T than C liver ( P < 0·05), as in lambs, but there were no other treatment differences in PTM concentration. Ewe and lamb tissue data were not directly comparable because they were exposed to different diets but mean concentrations of Cd, Ni and Pb were approximately two-to four-fold higher in ewe than lamb liver while mean Cu concentrations were approximately five-fold lower, suggesting that more prolonged exposure to PTMs may have enhanced treatment differences in tissue PTM concentrations. Mean foetal PTM concentrations were not significantly affected by treatment. It is concluded that the repeated application of sludge to pasture is associated with altered, but not necessarily increased, rates of accumulation of PTMs in liver tissue, that rates of accumulation depend on the individual PTM measured and that they are probably influenced by duration and route of exposure and source of nutrient. Limited observations suggested that there was little effect of year, and associated variation in climatic conditions and herbage growth, on PTM accumulation.

Exposure to pastures fertilised with sewage sludge disrupts bone tissue homeostasis in sheep

“…accumulation of several pollutant groups have been assessed for ruminants grazing pastures treated with sludge (Fries and Marrow, 1977;Smith, 1996) and concentrations of selected organic pollutants and heavy metals in sheep maintained on the same pastures as those in the present study have been reported (Rhind et al, 2007;Rhind et al, 2005a;Rhind et al, 2005b). Both predicted and actual concentrations of various pollutants in tissue, following exposure to treated pastures, including heavy metals and organic pollutants were low and not consistently increased, relative to control pastures.…”

“…Since these are known to exert adverse effects on animal and human physiology and health (IEH, 1999;Toppari et al, 1996), potential effects on wildlife, domestic animals and humans are of concern. Theoretical and empirical studies, designed to investigate the issue of accumulation of pollutants in domestic animal products, generally indicate that exposure to sewage sludge is associated with only limited tissue accumulation (Rhind, 2005;Rhind et al, 2005a;Rhind et al, 2005b;Smith, 1995) and so the risks to humans of exposure to pollutants through the consumption of animal products is likely to be small. On the other hand, previous studies of sheep grazing pastures fertilized with either sewage sludge or inorganic fertiliser have shown that exposure to EDCs and other pollutants through the sewage sludge can disrupt the development and function of the foetal testis (Paul et al, 2005), ovary (Fowler et al, 2008) and adult offspring behavior (Erhard and Rhind, 2004).…”

Bioavailability: Exposure, Dose and Risk Assessment

“…For example, it has been shown that small, individually nontoxic amounts of certain environmental pollutants can cause significant changes in animal physiology when combined with other pollutants at nontoxic levels [91]. Investigations looking at physiological responses of sheep grazing on pastures amended with sewage sludge applied at levels below regulatory limits have also revealed toxic responses [92][93][94], although the statistical significance of these findings is marginal. Measured concentrations of potentially toxic elements in sheep tissues have also been nonintuitive.…”

Anthropogenic pollutants: a threat to ecosystem sustainability?

“…to environmental (low) concentrations of multiple pollutants, through physiological routes and at all stages of the life cycle. In this study, the twice yearly application of sludge to the pastures resulted in only minimal increases in environmental (soil) concentrations of the organic pollutants phthalate and alkyl phenol (Rhind et al 2002) and variable but generally small increases in PAHs, PCB and PBDE (S. M. Rhind, C. E. Kyle, C. Mackie & L. Macdonald, unpublished observations) and heavy metals (Rhind et al 2005b), relative to concentrations found in pastures treated with inorganic fertilizer. These results agree with a review of earlier observations by Smith (1996) who reported that even extremely high rates of application resulted in increases in soil concentrations of not more than a few fold.…”

“…While much has been learned about both the potential effects and the mechanisms of action of individual compounds from such studies, they are usually a poor representation of normal, real-world exposure and are often based on single chemicals, often at very high concentrations and applied for short periods. In practice, massive exposures to single pollutants in the natural environment are rare but long-term exposure to low concentrations of multiple organic and heavy metal chemicals has become commonplace, as indicated by reports of detectable concentrations of some of the classes in air (Lee et al 2004;Tonne et al 2004), soil (Smith 1996;Rhind et al 2005b) and water (IEH 1999). However, controlled studies of the effects of exposures to these low-concentration mixtures are also rare.…”