Report No FR/D0029

Feb 1998

EXECUTIVE SUMMARY

The present report integrates the results from these research programmes, and discusses their implications for food safety and for animal health and production in relation to current limits on PTE concentrations in sludge-amended soils. Tissue accumulation of cadmium (Cd), lead (Pb) and copper (Cu) is assessed, both in a worst case situation with respect to soil intakes and soil PTE concentrations (soil at statutory limits) and under current operational condition. The main conclusions, taking into account PTE intakes from other sources, particularly herbage, are:

• Carcase meat from animals grazing sludge-amended pasture should be acceptable for the human food chain, as concentrations of Cd, Pb and Cu in muscle remained low during all of the trials.
  
• Cd concentrations in liver and kidneys, based on Cd transfer from ingested sludge-amended soil, do not suggest a need to tighten soil limits for Cd. However, elevated Cd concentrations in grass grown on sludge-amended soil combined with ingested soil Cd may result in unacceptable Cd concentrations in offal, particularly for a worst case scenario and the kidneys of aged livestock. Further information is needed on the relative bioavailabilities of Cd in soil, sludge and herbage, and on the supply of available Cd from other sources. Typical sewage sludges applied to previously unsludged soil will have little effect on offal Cd concentrations, but clarification is required on the extent of transfer of Cd after recent applications of sludge to grassland amended historically with sewage sludge.
  
• Soil ingestion by lambs and ewes grazing pasture sludged to the current statutory limit concentration for Pb is likely to result in kidney Pb concentrations approaching or exceeding the current limits for Pb in food but, due to the present higher limit for Pb in liver, most livers should be acceptable. There were wide variations in the accumulation of Pb in offal, both between animals and treatment groups, which could not necessarily be explained by differences in dietary Pb levels, but the dietary conditions under which offal Pb concentrations would comply with current legislation on Pb levels in food have not been clearly established. Small increases in soil Pb concentrations above background values resulted in disproportionately large increases in liver and kidney Pb concentrations.
  
• There are several possible consequences when sheep and cattle graze sludge-amended pasture, ranging from Cu depletion to accumulation of liver Cu, and potential Cu toxicity with sheep. The actual outcome will be highly dependent upon the balance between Cu supply and the presence of interacting factors, chiefly molybdenum (Mo), sulphur (S) and iron (Fe). Accumulation of liver Cu is most likely with low soil ingestion and elevated herbage Cu due to sludge-amendment. With inherently low soil Cu concentrations and high soil ingestion rates, sludge-borne Cu may alleviate marginal Cu deficiencies. Due to the general unpredictability of the Cu status of livestock, it is good agricultural practice to monitor Cu whenever the mineral status of soil is attenuated.
  
• Soil factors, such as physical type, chemical composition and pH, variously influence offal Cd and Pb concentrations, although their effects were generally relatively small, and not fully clarified. Copper from recently applied sludge appears to be more available to sheep than Cu from sludge which has equilibrated with soil.
  
• Transfer of Pb but not Cd across the placenta and in the milk was observed during the indoor feeding trials, but there are likely to be few consequences in practice for finished animals. Concentrations of Cu in the milk were not influenced by the ingestion of sludge-amended soils.

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