Betsy Lynch
June 14, 2010

Worms in soil

A study in India showed worms will ingest soil toxins without re-polluting the soil when they die.

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It seems earthworms may be the key to reclaiming contaminated soils in India and around the world.

Suneet Dabke, PhD, a consultant with Concept Biotech, spear-headed a four-year vermiculture bioremediation effort with the help of a grant from the Blacksmith Institute in New York and support of farmers and villagers in western India’s Muthia village. He shared his results at the 10th annual North Carolina State University Vermiculture Conference last month in Durham, N.C.

Muthia village is a small agricultural community near the city of Ahmedabad (population 5 million) in Gujarat state. Textile and pharmaceutical companies used the region as a toxic waste site, contaminating the land so thoroughly that farmers can no longer grow crops there. Chromium, lead, iron and zinc turned the ground yellow and also leached into the water supply. Today, the streams continue to run a sickly yellow, and water must be trucked in for the 7,000 villagers.

For decades, many factories in India dumped their toxic wastes onto the ground soil, unchecked and unregulated. In 1996, laws were passed to prevent further soil degradation, but the toxic legacy left behind continues to plague people’s health, productivity and environment. The initial findings from Dabke’s vermiculture project, in which he used earthworms and beneficial microbes to “eat up” soil contamination on 4 acres of land, show the soil may be reclaimed.

Dabke’s team started work on the site by removing 3½ feet of soil and disposing of it at a landfill. Working with area farmers who donated tractors, seed and labor, they then tilled compost into the subsoil, applied a microbial solution, spread vermicast (worm manure), and applied a vermi-accelerator, an inoculation of beneficial microbes in order to balance pH and create a more suitable environment for the worms.

Muthia Village, India

Courtesy Blacksmith Institute

Workers in Muthia village, India, treated contaminated soil with active bacterial inoculants and vermi-castings.

Prior to adding worms, they also grew a cover crop, tilling in a portion of it and laying some of it on top of the soil as mulch. Finally, Dabke and his team introduced 300,000 earthworms and let them go to work.

In addition to the beneficial affects of aerating and fertilizing soil, the worms consumed and processed soil organic matter. In the process, the worms were able to remove the toxins from the land because they retain ingested toxins in their body tissues rather than excreting it.

Before the study’s conclusion, the toxic worms were harvested from the site and burned in an incinerator. The rationale was that disposing of the worms by incinerating them would disperse any residual heavy metals into the atmosphere and would be less harmful to the environment and area inhabitants than letting the heavy metal-laden worms remain in the soil.

Environmental scientist and vermiculture specialist Norman Aracon, PhD, from the University of Hawaii, points out that as long as the worm population remains healthy and active, the heavy metals the worms ingest remain contained inside the worms’ body tissue. When those worms die, other worms and microbes ingest the worm proteins so the toxins remain sequestered and aren’t released and taken up by plants.

Theoretically, the toxins from dead worms would not be released into the soil unless all the worms in a region died. However, more research is needed in this area.

In similar vermiculture studies done in the U.S. using worms to remediate contaminated soils (such as in mine-reclamation projects), it has also been observed that as worms migrate, they help disperse toxins, reducing contaminant concentrations in a given area.

In vermicomposting systems used to process biosolids, such as human waste and sewage sludge from municipal waste-treatment plants, the residual worm castings typically pass EPA requirements for heavy metals and harmful pathogens. In other words, it appears that worms work as Mother Nature’s purification plants.

In the final phase of the Muthia-village study, Dabke’s team planted maize. Tests showed only trace levels of heavy metals in the soil and crop. Since the project’s conclusion, the region’s farmers have united in trying to get industries to accept responsibility for more remediation land projects so they can raise crops and graze livestock on safer soils.

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