A CITYSCAPE, snow, children shrieking with pleasure as they play in the
dwindling light of a winter afternoon鈥攖he scene could come from countless
urban locations. But a few months ago you would not have found kids playing in
Maria Carvelho鈥檚 back yard in a residential suburb of Boston. Nobody knows how,
but the land was contaminated with up to three times the recommended safe levels
of lead. The heavy metal was poisoning Carvalho鈥檚 two daughters, but now with
the help of some mustard plants they can play in safety. How the yard came to be
reborn is the story of an extraordinary collaboration between art and
science.
New York sculptor Mel Chin was in search of inspiration. He had spent most of
the 1980s building things, now he was looking for a new concept. The hunt led
him through a maze of social, political and economic ideas until one day in 1989
he chanced upon an article in the American environmental quarterly, The
Whole Earth Review, about using jimson weed to clean soil contaminated with
heavy metals. It sparked his imagination. Chin had a creative vision of taking
contaminated soil and fashioning it into a work of art鈥攃lean land. 鈥淭here
is this poetic idea that there is something dead, and through this process it
becomes alive again,鈥� he says.
There was only one problem: Chin knew nothing about plants. Enter Rufus
Chaney, a botanist with a passion for phytoremediation, the process by which
plants absorb pollutants from soil. In his lab at a US Department of Agriculture
centre in Beltsville, Maryland, Chaney had been testing the abilities of crop
plants to tolerate metals. Some, such as turnips, lettuce and lovegrass, die at
the merest whiff, while others, including maize and red fescue Merlin, thrive in
metal-rich soil.
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Toxic garden
Until then, phytoremediation had been an academic curiosity but, with Chin鈥檚
help, Chaney saw a way of taking it out of the lab and into the field. Chin鈥檚
idea was to design a garden or 鈥淩evival Field鈥� that would rejuvenate a
contaminated industrial site. Chaney suggested using some of his crop plants
together with small weeds known for their ability to extract metals from soil.
Plants like the white-flowered European alpine pennycress, a member of the
mustard family, accumulate toxic metals inside cellular compartments called
vacuoles as protection against chewing insects and infection.
Very little, however, was known about how to increase the metal uptake of
such plants, so Chaney suggested varying the conditions under which they were
grown so that Chin鈥檚 work of art would also be a scientific testing ground.
While Chaney pulled together appropriate plant species from around the world,
Chin went to work on getting a site. His attention was drawn to the old Pig鈥檚
Eye landfill in St Paul, Minnesota, near the Walker Art Center where he had some
art on display. Until the 1970s, this 120-hectare site had been used as a dump
for waste from incinerated sewage sludge, which was contaminated with cadmium
and zinc. But before Chin could get to grips with the site, he had to negotiate
with politicians, community members and lawyers working for and against the
polluting company.
It took almost two years, but in spring 1991 Chin at last began work on the
Pig鈥檚 Eye site. First he had to learn how to garden. But with a few tips from
Chaney and some durable gloves and face masks to keep the toxins at bay, Chin
and his two assistants created a space for the garden 20 metres square. The
design, a circle within a square, had walkways that formed an X, symbolically
targeting the site for cleaning. Chin was pleased with the result. 鈥淚t was
illegal to go on this field because of the contamination, but I had to know it
might some day be seen.鈥�
The pattern contained 96 test areas where maize,
Merlin red fescue, bladder campion, alpine pennycress and lettuce鈥攁s a
control鈥攚ere grown, using a variety of fertilisers and soil acidifiers.
Chaney hoped to identify which fertilisers worked best with each plant to
increase growth and the amount of metal absorbed. Acidifying the soil ionises
the metals, increasing their solubility and making them easier for plants to
absorb.
For the next three years, Chin鈥檚 assistant Tam Miller tended the garden,
adding fertilisers and acidifiers as required and monitoring growth. Each spring
the team dug up the plants to analyse their metal content, then replanted the
plots.
Alpine pennycress grown at low pH was best at getting rid of zinc and
cadmium. Normal plants cannot tolerate more than about 500 parts per million dry
weight of zinc, but the pennycress stored up to 25 000 parts per million. Chaney
calculated that pennycress could absorb the metal at an annual rate of 125
kilograms per hectare if the soil was acidified to a pH of 5 or 6. So a typical
contaminated site might take 16 years to clean. Chaney believes that with the
right strain of pennycress, or some genetic tinkering, this could be reduced to
four years.
Second revival
In 1993, with the first Revival Field well under way, Chaney suggested
another site to Chin. A zinc smelting plant had left this residential area of
Palmerton, Pennsylvania heavily contaminated with zinc and cadmium. This time,
people seemed more open to phytoremediation. With help from the Borough Park
Commission, the Zinc Corporation of America and the Palmerton Environmental Task
Force, Chin and Chaney created a fan-shaped garden. They tested a different set
of fertilisers and soil acidifiers, and they let the plants grow for three full
years rather than replanting each year.
Last year, the plants were uprooted. Once again, alpine pennycress led the
pack in uptake of zinc and cadmium. And the rate of absorption increased in the
second and third years. Building on these findings, Chaney has since analysed 20
strains of alpine pennycress from sites around Europe to identify the most
efficient cadmium absorber. He now plans to use it in China, where cadmium
contamination is a major health hazard, and has already started work in Eastern
Europe.
Chin鈥檚 gardening days are over. Without funding to continue the project, his
Revival Fields are now full of weeds. Even so, he is pleased with the impact of
his work. 鈥淲hen I hear from Chaney that companies are starting to sell the idea,
I feel like that means it was all worth it,鈥� he says. In the past few years,
Phytotech, the New Jersey-based company that made the Carvalho鈥檚 yard safe to
play in, has floated rafts of sunflowers to clean uranium-contaminated water
around Chernobyl and used pumpkins and mustard plants at the old Magic Marker
pen factory site in Trenton, New Jersey. And other phytoremediation companies
are springing up
Before Chin鈥檚 gardens, few people were working on phytoremediation, says
Chaney. Now, it鈥檚 a growing field.