Soil ingestion--a major pathway of heavy metals into livestock grazing contaminated land

An estimated 4000 km2 of agricultural land in England and Wales has been contaminated in varying degrees by past mining and smelting activities. Contaminants include one or more of the metals Cu, Pb, Zn, Cd and As. Studies conducted in southwest and central England conclude that only a small proportion of these metals are taken up into the leaf material of pasture plants and that plant uptake would not seem to constitute a major pathway to grazing animals. Using the titanium content of faeces as a stable indicator of soil ingestion, we found that grazing cattle involuntarily ingest from 1% to nearly 18% of their dry matter intake as soil; sheep may ingest up to 30%. Soil ingestion varies seasonally and with farm management. Calculations based on soil, plant and faecal analyses show that from 9% to 80% percent of the Pb and 34% to 90% of the As intake into cattle on contaminated land is due to ingested soil.