Long term use of heavy metal-rich sewage sludge could potentially harm soil quality and fertility, according to results of a DEFRA-funded study.

Elevated levels of metal-rich sludge were applied over four years at seven sites across England and Wales during the mid-90’s and it was found that cadmium, zinc and copper impacted on some microbial groups, resulting in potential long term soil quality implications.

But, the findings are by no means conclusive. Application rates used in the study exceeded current ‘Sludge Use in Agriculture Regulations’ and it would take over 100 years to reach such concentrations with normal field practice.

In addition, DEFRA said the sludge applied in the trial contained much higher concentrations of metals than were allowed in sludge used today and therefore did not represent current quality.

Further work was planned to understand the interactions between the heavy metals and soil quality and how they could be influenced by management practices.

The full report is available at the DEFRA website.