Earthworms could be used to extract toxic heavy metals, including cadmium and lead, from solid waste from domestic refuse collection and waste from vegetable and flower markets, according to researchers at Pondicherry University, in Puducherry, India.
Writing in scientific journal, the International Journal of Environment and Waste Management, the researchers explained how three species of earthworm, Eudrilus eugeniae, Eisenia fetida and Perionyx excavates can be used to assist in the composting of urban waste and to extract heavy metals, cadmium, copper, lead, manganese, zinc, during subsequent processing.
The researchers - Swati Pattnaik and M Vikram Reddy of the Department of Ecology and Environmental Sciences, at Pondicherry University - explained that with rapid increases in urban populations particularly in the developing world, there is a growing problem of how to manage organic waste and to find alternatives to landfill disposal particularly for domestic food waste and that from vegetable markets.
According to the research team, in India much of this waste is currently dumped on the outskirts of towns and cities and is causing serious pollution. It also represents a considerable wasted resource.
The process of vermicomposting using these species of worms allows such waste materials to be remediated and the compost used subsequently for use in growing human food without the risk of accumulating heavy metals in crops.
The team claimed that up to 75 per cent of the various heavy metals can be removed by the worms from solid waste.
The researchers found that the Eudrilus eugeniae species was the most effective worm for remediating solid waste and producing rich compost, with tests demonstrating that the heavy metal content of such waste can be reduced to levels significantly below the permissible safe limits.
The worms’ digestive system is said to be capable of detaching heavy metal ions from the complex aggregates between these ions and humic substances in the waste as it rots.
According to the researchers various enzyme-driven processes then seem to lead to assimilation of the metal ions by the worms so that they are locked up in the organism’s tissues rather than being released back into the compost as worm casts or vermicompost.
The separation of dead worms from compost is a relatively straightforward process allowing the heavy metal to be removed from the organic waste.
