Accumulation of potentially toxic elements by sheep given diets containing soil and sewage sludge. 1. Effect of type of soil and level of sewage sludge in the diet

Abstract

Increasing amounts of sewage sludge will be applied to agricultural land over the next 10 years as a result of the prohibition of its disposal to the sea. The addition of potentially toxic elements (PTEs) to the soil via sewage sludge is controlled by European legislation designed to limit the accumulation of PTEs in soil which could give rise to toxicity to plants or livestock. However the possibility exists that direct ingestion of sewage sludge and soil together with grazed herbage may result in accumulation of PTEs in body tissues. To assess the extent of accumulation of PTEs by direct ingestion of soil and sewage sludge 12 groups of housed weaned lambs were given diets ad libitum comprising dried grass (900 g/kg total diet dry matter (DM)) and three different soils (100 glkg total diet DM). Soil was replaced by dried digested sewage sludge at levels ofO (level 0), 75 (level 1), 150 (level 2) and 300 g/kg soil DM (level 3). Voluntary intake of DM was markedly depressed by the inclusion of sewage sludge in the diet (on average by 24 g DM per g sewage sludge DM addition). There was no effect of sewage sludge on diet apparent digestibility. Live-weight gain was depressed (P < 0·001) by the addition of sewage sludge to the diet from 236 glday (level 0) to 141 glday (level 3). Liver and kidney weights were also reduced (P < 0·01). The apparent availability coefficients for Cd, Pb and Cu increased with increasing level of sewage sludge in the diet fP < 0·05), as did their concentrations in the liver and kidney (P < 0·01). Concentrations of Cd and Pb in liver increased from <0·07 mg/kg DM and <0·40 mg/kg DM (level 0) respectively to 0·61 mg/kg DM and 4·60 mg/kg DM (level 3) respectively at the end of the trial. Similarly the concentrations of Cd and Pb in kidneys increased from 0·19 mg/kg DM and <0·56 mg/kg DM (level 0) respectively to 0·80 mg/kg DM and 7·10 mg/kg DM (level 3) respectively by the end of the trial. No increases were observed in concentrations of Cd or Pb in muscle tissue. The main effect of type of soil on concentrations of PTEs in body tissues was not significant The daily rate of accumulation ofPb in kidney ranged from 1·1 to 51·5 uglg daily tissue DM growth during the first 57 days of the experiment and from 0·33 to 6·78 /xg/g daily tissue DM growth between day 57 and day 112. A decrease in the second period was also observed for Cd, with accumulation in kidney ranging from 0·31 to 4·44 fig/g daily tissue DM growth during the first 57 days and from 0·21 to 1·44 /jg/g daily tissue DM growth between day 57 and 112. Concentrations of Pb in liver of lambs given the highest level of sludge approached the statutory limit set for human food. The results indicate that in relation to accumulation of PTEs in liver and kidney there would appear to be little margin of safety with respect to the current United Kingdom statutory limits for the concentrations of Cd and Pb in sludge-amended soils. Confirmation of these results is required in the grazing situation.

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

“…Despite the fact that Cu concentrations were slightly higher in T than C plots, concentrations were lower in T than C lamb tissues. This is also consistent with previous reports (Hill et al, 1998a and b) but in the present study this difference was shown to occur in ewe tissues as well as in lambs, although concentrations were generally higher in the latter. This apparent anomaly in the patterns of soil and tissue concentrations with respect to Cu, is probably a reflection of the many factors that affect assimilation in animal tissues.…”

“…While exposure to sludge had no significant effects on any of the tissue concentrations of Cd, Cr, Hg or Ni, as reported previously (Hill et al, 1998a and b), the results indicated that the patterns of accumulation of other metals differed with age and/or stage of development. Despite the fact that Cu concentrations were slightly higher in T than C plots, concentrations were lower in T than C lamb tissues.…”

“…While previous studies addressing PTM assimilation in weaned lambs offered sewage sludge (Hill et al, 1998a and b) or grazed on sludge-treated pastures ( Wilkinson et al, 2001 and2003a) have yielded much valuable information, they were not designed to address the effects of exposure to PTM at different stages of development. The present study illustrates the pattern of accumulation during the foetal stages of development and allows the effects of prenatal exposure to be separated from those of exposure postnatally, when animals had consumed either milk from exposed dams together with sludge-treated pasture (present study), or treated pasture only (previous studies).…”

Accumulation of potentially toxic elements by sheep given diets containing soil and sewage sludge. 2. Effect of the ingestion of soils treated historically with sewage sludge

“…An investigation of the accumulation of potentially toxic elements (PTEs) by sheep given diets containing different levels of sewage sludge (Hill et al, 1998) found significant increases in the concentrations of Cd and Pb in liver and kidney but not in muscle tissue. The rate of accumulation of PTEs, especially Cd and Pb, declined with increasing animal age and as the level of PTEs in the diet was reduced.…”

Determination of Heavy Metal in Agricultural Soils near and Far From the Cement Factory in Tehran, Iran

“…When evaluating livestock exposure to HMs it is important to consider that dietary exposure will be highly conditioned by husbandry practices, dietary ingredients, soil ingestion or spurious soil contamination in foliage being responsible for the main HM exposure [7][8][9].The HM contamination soils has become serious environmental issue around the world for various reasons, including industrial activities, solid waste disposal, fertilizers, pesticides, sludge application, irrigation with wastewater, and automobile exhausts [10][11][12][13].Beside, anthropogenic and geologic materials, soil character, mobility of the elements, weathering processes and environmental factors have remarkable effects on distribution [14,15]. It is important to have in mind how management practices can contribute to enhancing livestock metal exposures in order to minimize their toxic effect on animals, as well as to limit metal transfer to human feeds as much as possible.…”