A few comments by Michael Pilarski, Friends of the Trees Society.
[This paper was written for presentation at an Earth Repair workshop I did on Vashon Island on November 19, 2016.]
Vashon/Maury Island was in the contamination plume of the ASARCO copper smelter in Tacoma. The ASARCO smokestack was once the world's largest. It was demolished in 1993. Cadmium, arsenic and lead are all involved. The south end of the island was more affected than the north end.
In preparing for my Vashon Island talk I had a phone conversation with May Gerstle of the Heavy Metals Remediation Committee of the Vashon-Maury Island Community Council (which is no longer active). May said that there was a lot of energy around this some decades ago but there is a lot less talk about it now. Some of their information is still on the internet.
I am somewhat familiar with the issue from having done research on arsenic and lead contaminated soils when I was farming in the Okanogan valley and a lot of old orchard soil was contaminated with arsenic and lead from the early insecticides. I was thinking of leasing one of these sites and my young son would be assisting me in farming. I decided against the lease because of the dirt and dust exposure of my son, young interns and myself.
When I was doing the research I had the opportunity to have a phone conversation with the State’s leading heavy metals expert, who was about to retire. My recollection of what he told me was that the arsenic and lead tended to move down in the soil and settle at around 18 inches. So deep working of the soil is discouraged. Crops grown on soils which have a high organic matter content and are biologically active do not take up the heavy metals near as much as poor soils. So developing a rich and biologically active and diverse web of life in your soil is what you are aiming for, particularly if you are growing food or herb crops.
No-dig, organic systems based on perennial crops are recommended. Forest gardens, permaculture, Ruth Stout, Emilia Hazelip type of systems. I highly recommend watching the 30-minute film The Synergistic Garden. An educational video on no-till synergistic gardening that describes the step-by-step processes developed by Emilia Hazelip to create an ecological agriculture. In this video the long-time, French permaculturist explains her gardening systems for temperate regions. It would be one of the safest ways to grow food on contaminated soils.
Different parts of plants are more likely to pick up contaminants. Fast growing leafy greens are the most likely, then root crops (need thorough washing, perhaps peeling), then seeds. Fruits are the most safe. Of course, there are many crops that aren’t ingested such as fiber plants, willow and basketry plants, bamboo, dyes, etc.
One option for badly contaminated soils is to cap them with various hard or impermeable surfaces. There is a famous garden in Philadelphia which grows on a capped, super-fund site and which grosses hundreds of thousands a dollar per year by growing in greenhouses, containers and beds made of brought-in materials. Capping with plastic sheets and creating raised beds is possible for gardens. Using hugelkultur raised beds on capped or uncapped soils is an appropriate growing method.
In some cases the contaminated dirt is dug up and hauled away to special hazardous materials sites. This is expensive.
Growing and harvesting plants which are accumulating the contaminants in question is another strategy. The harvested parts are sent to a hazardous waste disposal site or a smelter to reclaim the metal. Gradually the harvests of plant mass lessen the pollutant(s). Horsetail, for example, is good at picking up heavy metals. Foxglove and sunflowers have been mentioned in this regard. What has been tried on Vashon-Maury? What is the state of the art on heavy metals and myco-restoration? Cleaning up sites with fungi and harvesting the mushrooms for disposal.
While some people argue that soil processes and life can transmute some elements, I have never heard that argument applied to heavy metals. They are going to be around for a long time.
Here is a recent book:
Heavy Metal Contamination of Soils: Monitoring and Remediation (Soil Biology)
Nov 18, 2016
by Irena Sherameti and Ajit Varma
$159 on Amazon
Free soil tests are available through King County for arsenic and lead: http://www.kingcounty.gov/healthservices/health/ehs/toxic/TacomaSmelterPlume.aspx
contact 206-477-DIRT (3478); email us at [email protected]