It has recently been discovered that 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. 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, prior to subsequent processing. Since the population is rapidly increasing, 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. A lot of waste is currently dumped on the outskirts of many towns and cities and is causing serious pollution, disease risk and general ecological harm. It also represents a considerable wasted resource, whereas the organic matter might be exploited usefully in growing food crops. The process of vermicomposting in this way 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 making it safe for everyone. How this possible one might ask? Well the worms' digestive system is apparently capable of detaching heavy metal ions from the complex aggregates between these ions and humic substances in the waste as it rots. Various enzyme-driven process 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. The separation of dead worms from compost is a relatively straightforward process allowing the heavy metal to be removed from the organic waste.
http://www.sciencedaily.com/releases/2012/08/120816133420.htm
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