Agroscope, Institute for Plant Production Sciences IPS, 1260 Nyon, Switzerland

Contamination of soil by sewage sludge and other fertilisers

The heavy metal load to Swiss soils decreased significantly in past years. Nevertheless, the input still is considerably higher than crop uptake. Fertilisers contribute around 50 % to the load of most metals, except for chromium and zinc with 90 % and 80 % respectively. Sewage sludge contributes 42 % of the lead, 26 % of the copper and 24 % of the cadmium load but only 9 % of the phosphorus input in fertilisers. In comparison to other fertilisers the quality of mineral fertilisers and manure, expressed as metal to nutrient ratio, is considerably better than that of sewage sludge. Nevertheless, this comparison and an assessment of the ecological relevance of different metals show that the uality of sewage sludge is better than that of compost produced from separately collected organic wastes and of other organic residues used as fertiliser.

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