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With new suggested EU threshold values for six heavy metals in fertilisers, the amounts of heavy metals found in mineral fertiliser are unlikely to harm soil organisms and as a consequence soil quality.

This has been established by scientists at Aarhus University after comparing the concentrations of a number of heavy metals in mineral fertiliser with relevant knowledge of ecotoxicity levels. The reason for the investigation is the proposal by the EU to introduce new thresholds for metals in mineral fertiliser; a proposal that has been designed to counter the potential environmental risks associated with high concentrations of heavy metals. The analysis involved a short-term and a long-term risk assessment of the heavy metals supplied with mineral fertiliser.

The scientists developed eight typical scenarios for the use of mineral and organic fertiliser in Danish farming. They estimated the quantities of heavy metals supplied with the different scenarios and the soil concentrations immediately following application.

To determine whether concentrations exceeded the limits, they compared them to the ecotoxicological thresholds that have been established previously. From this comparison they conclude that the metals do not constitute a short-term risk for soil quality.

To establish whether there is a long-term risk with repeated applications over many years, the scientists compared the estimated quantities applied with the so-called critical loads, which is the annual deposition of heavy metals that an ecosystem can cope with in the long term.

There are no up-to-date critical load figures for Denmark so figures for the Netherlands were used instead. From these figures they can conclude that there does not appear to be a long-term risk either.

However, a reduction of the thresholds for nickel, chromium and lead should be considered, the scientists recommend in their report ”Ecotoxicological evaluation of As, Cd, Cr, Pb, Hg and Ni applied with fertilisers in Denmark”.

The development and use of models and critical loads for calculating the long-term acceptable inputs of metals under Danish conditions will improve the basis for the evaluation.

February 2012