THE SCIENTIFIC BASIS TO RECYCLING SEWAGE SLUDGE IN AGRICULTURE

摘要

The environmental effects of heavy metals in sewage sludge-treated agricultural soils are examined in this paper. The scientific evidence shows that the potential environmental risks from heavy metals applied to soil in sludge are small and that precautionary, technically based soil quality limits for metals can provide a pragmatic approach to facilitate recycling. Because they encourage recycling, they also provide an incentive to reduce metal discharges to sewers to enhance the environmental and operational sustainability of the agricultural outlet for sludge management. This is discussed within the context of current proposals to reduce the maximum permissible limit values for heavy metals in a revision of European Directive 86/278/EEC regulating the use of sludge in agriculture. The revised values are lower than precautionary, scientifically based soil limits. Copper is the most limiting element and the standard proposed for this metal would restrict the maximum number of applications of sludge to a particular field to 25, assuming an application rate of 5 t ds y~(-1). Unless the European Commission can be persuaded to adopt a moderately more flexible approach to regulating PTEs in soil in the revised Directive, this short horizon may compromise the operational viability of sludge recycling operations under UK conditions.