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Re: Lead bioremediation in gardens
I'm not a certified permaculturalist or anything fancy....
I happened to read an article just last night that may help in this
situation.... from National Geographic, August 1993,
"Bacteria: Teaching Old Bugs New Tricks"....
"Lethal cyanide poured daily from the Homestake Mine's gold
processing plant into South Dakota's Whitewood Creek. Mercury,
arsenic, and sewage thickened the toxic flow.... A Homestake
biochemist said "I thought bacteria could do it [clean up the
cyanide]. I collected samples of water exposed to the poison.
They held cyanide-tolerant bacteria that actually feed on the poison's
carbon and nitrogen. We designed... a series of tanks in which
the cyanide effluent moves slowly past feeding bacteria. It
"....Groundwater Technology, Inc. of Norwood, Mass [are]
specialists in treating polluted groundwater and soil. They have used
the technology of bioremediation to clean up hundreds of sites around the
".....[The author] sought out some sore spots... a Superfund
project on the lower Mississippi... the soil [was] black with
contaminants --- more than 200 toxic compounds.... [A biochemist with
Louisiana St. University] identified bacteria that were already eating the
pollutants and encouraged them to reproduce. [They were] applied to a
contaminated test site. In nine months they cleaned it up.
"....Aviation fuel had been leaking from [a Traverse City,
Michigan Coast Guard] station's underground tanks, maybe for decades.
Its invisible plume had moved a mile with the groundwater [contaminating
wells]. Traverse Group, Inc, a bioremediation firm, drilled
interdiction wells to pump out the fuel at the station boundary. The
effect on the plume was astonishing. With the spread of
the spill halted, the indigenous soil microbes quickly did their work, and
the plume collapsed on itself. After 18 months no trace of it was
found beyond the station." [End of excerpt]
Why not try a cheaper easier solution to your lead-infested parking lot
soil first, before buying expensive topsoil..... Till or plow
deeply, adding copious amounts of compost and rough, rotting organic matter like
moldy hay or straw.... Water the soil thoroughly and keep it
moist for several weeks..... then have it retested and see if the lead
levels are dropping... It seems to me that since the soil had been
sealed off from the air by the asphalt pavement, helpful bacteria had no
opportunity to flourish.... Perhaps all they need is some air (deep
rototilling and coarse organic additions), micronutrients (compost and water),
and some innoculation (compost and moldy hay)..... and the dormant,
lead-eating bacteria will clean up this site FOR you...??
Why not be a "test case" for this method, since you already have
an investment in one official lead test.... Your results could be very
helpful for others encountering the same problem..... If it doesn't work,
you can always resort to the more expensive methods (imported soil, raised
beds, etc.) I'm betting your soil cleans itself up....
Could I be mistaken? I'm no biochemist, either... But it
sounds reasonable, even with heavy metals.... Bioremediation works on
industrial sewage full of heavy metals..... Harwich, Mass. has a sewage
treatment facility that turns the town's residential and industrial sewage into
clean water, using only biological processes....
Thanks for listening...
Mrs. Joy Banks in AZ
>I'm helping to start a garden on
a site that was a parking lot. After
>depaving, we got the soil
tested for lead and it came back with 700 ppm.
>Some extension services
say this is "safe to garden" as long as you wash
with soap and don't grow roots or greens - in other words almost
>We're going to do more detailed spot
testing to see if it's only in certain
>areas, and if it's just one spot
we'll probably dig that out and fill it
>with city compost. In the
meantime I am trying to find out what we can do,
>particularly what crops
are safe to eat, and what we can grow that would
the stuff that we could then harvest and landfill
>(or smelt!). I
heard of one person who grew a particular variety of corn
lead-contaminated site, then smelted the corn to obtain a lead ingot
was an art project). The extension services all say corn, like
>fruit/seed crops, is safe, but maybe the lead accumulates in the
>husks. I would love to find out what variety of corn this
> If you have any advice, contacts, books, etc, to
suggest, I would be grateful.
>Mariposa Grove Community Garden
>Oakland, CA 94609