The significance of lead entering the human food chain via livestock ingestion from the agricultural use of biosolids, with special reference to the UK

Long-term application of biosolids to agricultural soils results in the slow accumulation of potentially toxic elements (PTEs), which are regulated by maximum permitted limit values to protect human health and the environment. Two programmes of UK government-funded (MAFF/DoE) research were commissioned in the 1990s to investigate the safety of the controls on PTEs in relation to the potential transfer to the food chain via the animal ingestion route by sheep grazing biosolids-amended soil. Here, we re-examine this evidence in the light of other recent research and revised food quality standards, to determine the significance of lead (Pb) accumulation in soil from the agricultural use of biosolids. Direct ingestion of biosolids-amended soil is the main transfer pathway of Pb to grazing livestock. The concentrations of Pb in muscle tissue of animals grazing biosolids-amended soil observed in the MAFF/DoE trials, and reported in the scientific literature, were generally small and similar to background, control values. Lambs and ewes ingesting biosolids-amended soil with a total Pb concentration > 200 mg kg−1 ds at a rate of 10 % in the diet exceeded the current maximum permitted concentration of Pb in offal (0.5 mg kg−1 fresh weight (FW)). However, the decline in PTE concentrations found in biosolids, due to improved industrial practices and stricter controls on the emissions of contaminants to the environment in general and wastewater in particular, has mitigated the risk of Pb accumulation above the food quality standard for this element in offal. Given the significant improvements in biosolids quality, and particularly the Pb content, regulatory soil and sludge limits for Pb are no longer likely to have a practical or significant impact on the amount of Pb entering the food chain through the animal ingestion route from biosolids-amended agricultural soil.