August 20, 2012
Heavy Metal Soaked Up By Earthworms
redOrbit Staff & Wire Reports - Your Universe Online
Using Worms For Bioremediation Of Toxic Metals
According to researchers writing in the International Journal of Environment and Waste Management, earthworms could be used to remove toxic heavy metals, including cadmium and lead, from solid waste from domestic trash collection and waste from vegetable and flower markets.
Three species of earthworm, Eudrilus eugeniae, Eisenia fetida and Perionyx excavates can be used to help in the composting of urban waste and to extract heavy metals, cadmium, copper, lead, manganese, zinc, prior to subsequent processing, explained Swati Pattnaik and M. Vikram Reddy of the Department of Ecology and Environmental Sciences, at Pondicherry University, in Puducherry, India.
With urban populations rapidly increasing, particularly in the developing world, managing organic waste and finding alternatives to landfill disposal, particularly for domestic food waste and that from vegetable markets, has become a growing problem. It is an unfortunate fact of life that much of this waste is now being dumped on the outskirts of many towns and cities and causing serious pollution, risk of disease and general ecological harm, according to the research team. It also represents a big wasted resource because the organic matter might be useful in growing food crops.
Waste materials can be remediated through the process of vermicomposting in this way and the compost used for use in growing human food without the risk of heavy metals accumulating in crops. The worms can remove up to about three-quarters of the different heavy metals from solid waste, the team said. The E. eugeniae species was the most effective worm at remediating solid waste and producing rich compost. The heavy metal content of such waste can be reduced to levels significantly below the permissible safe limits, the team's tests on vermicomposting revealed.
The worms' digestive system is apparently capable of removing heavy metal ions from the complex accumulation between these ions and humic substances in the waste as it rots. Various enzyme-driven process then seem to lead to absorption 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. The separation of dead worms from compost is a relatively straightforward process allowing the heavy metal to be removed from the organic waste.