Contaminants Management

Anecdotal evidence has suggested that vermiculture will reduce heavy metals through the accumulation of the metals in the worm biomass. Our research on this phenomenon is inconclusive. Reductions of 10 to 20% have been identified, but not uniformly across all metals.Notwithstanding the above, the impact of heavy metals is reduced by two mechanisms.

Firstly through dilution. The relatively clean additives provide a 20 to 30% reduction in concentration. Secondly, vermicast is used at relatively low application rates compared with traditional biosolids and compost application rates.

The maximum recommended application rate is 5 tonnes per hectare compared with over 40 tons per hectare for biosolids. This reduces the potential soil metals loading by over 80%.

A report by the Queensland Department of Natural Resources (DNR) "concluded that the impact of heavy metals on the soil could not be detected using standard analytic techniques". 

The Department of Natural Resources report was prepared using the data on Redland sourced vermicast and can not be extrapolated to all sludge. Local contamination levels must be assessed. However, the principle should be considered in establishing the regulatory framework for metal load levels.

Vermitech has developed a model for determining soil loading levels of different metals with varying concentration levels and application rates.