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Vegetables clean up in Leadville

A US study is increasing understanding of how common garden plants such as carrots, spinach, radish and mustard absorb heavy metals. Bill Holdsworth reports.

A 'greenhouse' built deep in a 3km long toxic mine tunnel in the Rocky Mountains could revolutionise the way hazardous concentrations of trace metals are removed from water.

Using common garden plants such as carrots, spinach, radish and mustard, the technology now being developed allows for the recycling of the extracted metals and a benign product use of the extracting agent.

The man behind the greenhouse is Frank Burcik. With more than 40 years' experience in the mining industry, he had long sought ways to reduce the environmental damage that mining can bring. In 1993 he established Water Treatment and Decontamination International (WTDI), one of the first companies to investigate cost-effective technologies aimed at reducing environmental liability and operational cost. Its application of the biological properties of certain plants allows a multiplicity of heavy metals and other contaminates to be removed.

Early pilot studies using spinach and mustard plants in the Leadville Mine Drainage Tunnel proved that 71% of heavy metals could be removed from 22 litres of water per minute over a 1.8m run of plant shelves.

Sitting at an elevation of more than 3000m in the Rocky Mountains, Leadville, Colorado has a colourful mining history.

Silver and other precious metals have been mined there since the Spanish arrived from Mexico in the 16th century. It lies at the centre of a vast river system flowing into the Missouri and Mississippi to the east and the Rio Grande to the south, cutting through the Grand Canyon with the Colorado River to feed the populous cities of western California.

In Colorado, the highest state in the US, agriculture comes into environmental conflict with mining.

It is the main US producer of coal and uranium. Radium, vanadium, gold, zinc, silver and lead are also mined. At Leadville, the world's largest mine, Climax, extracted molybdenum - a metallic element resembling chromium and tungsten, used for strengthening and hardening steel.

Climax and many other mines are now closed. Jobs are hard to find and, like the polluted waters from the mines, people are leaching away.

Leadville has a reputation as one of the 'dirtymen' of the nation, with some of the highest concentrations of toxic and hazardous trace elements leaching into river and water supply systems.

Frank Burcik's deep mine 'greenhouse' is being seen as a catalyst for reviving the fortunes of an ailing town, creating new jobs and cleaning away its reputation of being a 'dirty old town'. The importance of Burcik's work has brought much needed federal government investment from the Environmental Protection Agency (EPA) via its 'Superfund'.

The fund became a critical part of the US National Environmental Policy Act signed by President Nixon in 1970. The programme was initiated in the wake of the waste hazard that developed at Love Canal in Niagara Falls, New York. The EPA has an inventory of hundreds of hazardous sites across the US and the programme allows the agency to support individual states in cleaning up dangerous sites. In 1989 the programme was given further clout by the requirement for each state had to assure the EPA of its capacity to dispose of all hazardous wastes by 2001, or face the loss of federal funds.

At election time environmental issues tend to become a political football, but Superfund activities have generated intense public interest, involvement and political support. The public, through the Community Right to Know Acts, are able to gain access to information about the presence of hazardous chemicals in the community and any potential releases into the local and regional environment. This legislation enables federal, state, local government and industry to report emergency planning actions to the community. Such legislation and its attendant democratic action is still absent in the UK.

In Leadville, Frank Burcik's entrepreneurial ideas have led to the creation of a budding non-profitmaking Institute of Science and Technology and the promise of a new global impactive industry.

Since January of this year a phytoremediation system - as the technology is called - has been designed to treat 38 litres a second along a 140m length of the Leadville tunnel.

The tunnel allows complete control of air and water temperatures, water pH, growth medium, humidity, and light intensity and duration. All are growth factors that can be controlled to maximise growth and thus remediation.

The involvement of three different departments of Colorado State University (CSU) - Environmental Health, Biology, and Soil and Plant Sciences - shows a growing interdisciplinary effort in the project.

Quinoa, Indian mustard and yarrow are being grown in three 15m long hydroponic channels.

Each channel has four compartments, one for each of the plant types, while the fourth has a mixture of all three. Each channel is divided longitudinally into three different growth media: sand, nutrient film technique (NFT) or glass beads.

Flow rates through the channels are varied while all channels are supplied with constant levels of fertiliser and light. The plants grown in the NFT are first propagated at Colorado State University in a greenhouse on agar nutrient and then sand before transfer to the Leadville Mine Drainage Tunnel. Samples of water and plant material (roots and shoots) are then analysed for metal content in Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES).

The project is also testing the efficiency of duckweed, a generic term for several species of small aquatic plants with 90% water content. Duckweed allows for very high concentrations of contaminants after drying of the plant matter, greatly reducing the amount of material requiring disposal.

Burcik says: 'While plants found in wetlands have been used with only modest success in other clean-up efforts, my secret has been to harvest the saturated plants and reseed new ones.'

He has invented a technology that can mill profitable amounts of metal from the crop and allow the crop residue for the manufacture of particle boarding.

'Our investigative work has already proved the ability of WTDI's proprietary phytoremediation system to remove 80-95% of toxic trace elements and other contaminants from mine water in a range of conditions, ' he says.

Burcik talks about mine tailing contamination, stream and river pollution and radioactive materials including nuclear soil's contamination. The successful testing at Leadville has already provided ample data to move from the demonstration project into a fullscale underground agricultural remediation enterprise, he says.

Robin Littlepage, who on the strength of the new technology founded the Leadville Institute of Science and Technology last September, believes that a new dawn is breaking over the town.

'Leadville need not flounder any longer. Our goal has been to come up with long-term economically viable solutions, and ours are not just pipe dreams, ' she says.

'The EPA is hoping that the intense six-month experiment will enable the future clean-up of nine retaining ponds of highly acidic waste-rock drainage and thousands of gallons [tens of thousands of litres] of toxic waste water that looks just like Turkish coffee.

'We believe that we can do this, and it will need further help from the Superfund to ensure that we can extend our capacity deep in the mountain. We are also aware of other spin-offs that can expand the use of the plants after phytoremediation to post-treatment medicinal, agricultural and other markets, ' Littlepage remarks.

'Leadville can become the centre of a new vision in the environmental business and create new regional, national and global industries.'

Test plants

Quinoa (Chenopodium quinoa).

Because of its high productivity and nutritional values, this was considered in NASA's Controlled Ecological Life Support System. The plant also has a high amino acid and mineral content. It is unclear how much metal accumulation will affect nutritional properties, so Duane Johnson of Colorado State University's Department of Soil and Plant Sciences has been given a special brief.

Indian mustard (Brassica juncea).

This has several properties that make the process of phytoremediation more efficient. One of those is the genetic manipulation of the host plant.

Elizabeth Pilon-Smits of the Department of Biology at CSU has the task of developing transgenic lines of Indian mustard that overproduce heavy metal binding peptides (properties) and show enhanced cadmium accumulation and tolerance. This will be the first time that transgenics are being tested for their metal tolerance and accumulation.

Yarrow (Achillea millefolium).

Yarrow was used in the early experiments by Frank Burcik and displayed high promise for metal removal. It is a medicinal plant which has been used for a variety of treatments, from nosebleeds to antiinflammatories. Its historic name, Soldier's Woundwort, refers to its ability to stop bleeding. The demonstration study will also investigate how elevated metals' concentrations affect its medicinal properties.

Duckweed (Lemna minor)

An important plant for safe extraction of heavy metals. Several laboratory experiments have shown that Lemna minor can absorb up to 4000 ppm of zinc, measured by dry weight, copper 6714 ppm, 1.33% cadmium and 0.47% silver also by dry weight. However field usage has been restricted up to now to municipal wastewater treatment, livestock and industry.

In the Leadville Mine Drainage Tunnel demonstration treatment water from the yarrow process was used for the preliminary testing of duckweed. The duckweed was then grown in static trays with the LMDT run-off water.

Samples of water and duckweed tissues are taken every 12 hours for a 14-day acid digestion and ICP-AES analysis. The results are being marked on a timeconcentration curve, which will then indicate the optimal time for future retention treatment.

Techniques

Phytoremediation is the use of plants to remediate environmental pollution. The Leadville Mine Drainage Tunnel demonstration project was principally concerned with phytoextraction and rhizofiltration.

In phytoextraction, metals are bioaccumulated in the plant shoots. When the shoots are harvested, the metals are recovered (phyto-mining). The safe disposal or beneficial use of the harvested biomass and the safe storage of the highly toxic metals extracted are a critical part of the demonstration project.

Rhizofiltration is similar to phytoextraction, except that accumulation is in the roots.

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