Agricultural Livestock: Assessment of Copper Exposure and of Toxicity and Deficiency

Published 2005

Summary

Copper and its compounds, together with other metals, are considered within the European Commission’s Technical Guidance Document on Risk Assessment (TGD) as a class of chemicals of natural origin. Ambient concentrations of copper in the environment can thus be attributed to natural geochemical sources of the metal together with anthropogenic inputs that may have accumulated over time. Inputs of copper to the soil are to a degree countered by outputs which include uptake and removal in crops and pasture herbage and removal through erosion, leaching and downward migration. For example, it has been estimated that pasture herbage removes some 40-60 g Cu per hectare per year from the soil and that a similar amount is ingested by grazing cattle (both as herbage and soil). This is roughly compensated for by the return of copper to the soil in animal feces (MAFF, 1982).

The TGD is also concerned with bioaccumulation resulting from all exposure routes – air, water, soil and food and biomagnification – “accumulation and transfer of chemicals via the food chain, resulting in an increase of the internal concentration in organisms at higher levels in the trophic chain.”

Secondary poisoning is concerned with “toxic effects in the higher members of the food chain which result from ingestion of organisms from lower trophic levels that contain accumulated substances.” Agricultural livestock can be regarded in this category as their diets largely comprise pasture and forage plants and/or feedstuffs manufactured from crop plants. Because copper is an essential micronutrient for both plant and animal growth and health, this assessment must take into account issues concerned with deficiency as well as toxicity.

This review is restricted to agricultural livestock – cattle, sheep, pigs and poultry – that are primarily destined for human consumption and to the food chain transfer (soil to plant to plant-eating animal and soil to animal). It is based almost exclusively on cattle and sheep, as pigs and poultry are reared on formulated rations, which meet their dietary requirements, are usually raised under housed conditions, and may receive additions of copper compounds to promote growth. However, copper-rich excreta and slurry from pigs and poultry are sometimes intentionally applied or accidentally discharged onto pasture resulting in elevated copper exposure in grazing livestock.

The approach taken will be based on the concept that soil is an important source of copper to agricultural livestock (ruminants) via the food chain and that natural copper concentrations in soils vary widely in relation to the geochemical nature of the soil parent material. An assessment will be made of ranges in natural and ambient background concentrations of copper and of factors influencing the pathways soil-plant-animal and soil-animal (i.e., direct soil ingestion). Exposure will also be related to dietary feedstuffs, including hay and silage, growth promoters and mineral supplements. Information on copper levels in edible animal tissues will contribute towards human health risk assessment.

Critical values of copper in soil will be derived taking into account both natural and ambient background values for copper and will aim to provide a safe threshold for both toxicity and deficiency. It will be important to assess copper concentrations in soils related to the range of copper sufficiency in the diet within which neither deficiency nor toxicity may be expected in grazing ruminants.