Sunday, May 24, 2009

Brownfield Remediation For Urban Homesteaders

Urban homesteading is a very valuable skill set for the times we now face. One of the most important aspects of urban homesteading is for city dwellers to learn to grow their own food. A unique challenge of growing food in an urban or suburban environment is dealing with pre-existing pollution or contamination of an urban garden site. Such sites are known as “brownfields” as opposed to uncontaminated virgin lands called “greenfields.” Brownfields are common in urban areas and we must learn to deal with them, because as the existing “official” food economy deteriorates, we won't be able to just keep going to the store rather face this challenge. Knowing how to garden successfully on brownfields may soon mean the difference between surviving and starving.

Our Endangered “Official” Food System

The food production and distribution system that now exists in the industrial world is becoming increasingly endangered. This system depends on the concentration of control of vast amounts of farmland, labor, machinery, storehouses, distribution facilities and farm “inputs” in the hands of a few large corporations. These corporations distribute food through a vast global network of supply chains that lead to points of sale at local supermarkets. The whole system depends heavily on artificial means of forcing increased production from the ground that is farmed – means such as mechanized farming, pesticides, fertilizers and long-haul transport. All of these artificial means depend on fossil fuels and the cheap credit that a fossil-fueled economy provides.

Now that fossil fuels are becoming scarce, the entire system is beginning to break down. During the last oil price spike, the prices of petroleum-based fertilizers and pesticides also spiked. During the economic collapse that occurred afterward, lines of credit to farmers were wiped out, just as lines of credit for other businesses also dried up. Farmers have come to depend on credit in order to buy the seeds, fertilizers and other amendments, and machinery for each year's harvest. The reduction in availability of credit is causing farmers to cut back on planting. Several news reports predicted in 2008 that this could result in decreased harvests in 2009, leading to price spikes for food, and possible shortages.

This story will play itself out repeatedly and with ever-increasing severity as oil becomes scarcer and the official economy continues to deteriorate as a result. Under such circumstances, city dwellers will need to farm whatever pieces of ground they can get their hands on. Telling such people that it's safer to get their food from the store is a non-starter. Yet it is important to know how to garden safely in urban soils, and how to deal with contamination. In this post, I will focus mainly on dealing with lead contamination. Future posts may delve into how to deal with other kinds of contamination.

Dealing with lead contamination is a multi-pronged strategy consisting of the following elements: appropriate plants, separation techniques, and remediation tools.

Appropriate Plants

All plants accumulate lead to some extent; however, not all plants concentrate accumulated lead in their edible parts. A study performed by the Argonne National Laboratory examined lead accumulation in edible parts of food plants, the results of which showed that lead generally does not concentrate in the “fruit” of fruiting edible plants. These plants include things like fruit trees, corn, cucumbers, peppers, squash, tomatoes, watermelon and zucchini. Therefore, when dealing with heavily contaminated soils (soils that test over 400 parts per million for lead) that cannot be remediated due to cost or lack of access to resources, plants such as these should be cultivated, along with legumes such as beans and peas. Quite a lot of plants can be safely harvested and eaten, even when grown in heavily contaminated soils.

Once the fruiting parts of these plants are harvested, the crop should be washed thoroughly before use. Some sources recommend washing with both water and detergent. Afterward, these crops are quite safe for human consumption. However, it is generally not safe to eat root vegetables, leafy greens or herbs grown in soil contaminated to 400 parts per million or above. Safe utilization of these vegetables requires appropriate separation techniques.

Separation Techniques

When raising root vegetables and other crops susceptible to lead contamination, it is essential to keep these vegetables away from the source of contamination. Therefore, when gardening on a contaminated site, one must not plant these vegetables directly in the soil. Instead, raised beds or containers should be used. Clean soil should be placed in the beds or containers, and the soil should be monitored every season to insure that it does not become contaminated by windblown dust from adjacent contaminated areas. Wind-caused cross-contamination can also be reduced by planting a cover crop of grass in areas of bare dirt to immobilize the soil, as well as by mulch or weed tarps.

Suitable containers for container gardening are easy to come by, free of charge. One can find used five-gallon food-grade plastic buckets at many restaurants and supermarkets. Empty plastic detergent buckets are also good. As far as raised beds, some sources recommend placing a semi-permeable barrier at the bottom of the bed to separate the contaminated soil from the new clean soil added to the bed. The beds must be deep enough that any root vegetables grown in them will not contact the contaminated soil underneath even when they have grown to their full extent.

Gardening in raised beds or containers limits the size of the harvest available to an urban household. In order have the freedom to grow anything anywhere at any time on an urban homestead, soil remediation techniques must be employed where contamination exists.

Remediation Tools

Techniques of remediation of lead contamination have been studied extensively by non-profit urban gardening groups, non-governmental organizations (NGO's), universities and researchers affiliated with the governments of the United States and several other nations. Interest in lead remediation has risen as governments and others have come to grips with some of the negative effects of massive industrialization. The techniques studied have varied in complexity, reliance on advanced technology and cost, with the governments of First World nations tending to favor study of the most costly and complex techniques. These techniques include things like soil removal and replacement, soil washing, electrokinetic methods, and other costly remedies.

Such techniques are beyond the reach of most residents of the Third World, as well as most poor and middle-class people in the First World. I will therefore focus mainly on those techniques which have been studied for use in poor settings by people of limited means.

First, there are techniques of binding lead in soil to reduce its bioavailability to plants. One method, studied in China and in the U.S., involves adding rock phosphate and/or phosphate fertilizers to contaminated soil. The phosphates bind to the lead to form insoluble lead phosphate compounds that are not taken up by plants. Another method is simply to add compost to contaminated soil, as the organic compounds in the compost accomplish the same goal of immobilizing and binding lead in soil.

Then there is phytoremediation, which consists of growing plants that are known lead accumulators in order to reduce the total concentration of lead in soil. Some phytoremediation strategies promise a reduction of 100 parts per million per growing season. Reduction of soil lead levels to an acceptable range by this technique takes from two to over five years. It should be viewed as part of a long-range strategy for healing urban areas.

Final Thoughts: The Correct Way To Assess Contamination Risks

This week's post is a follow-up to my earlier post, “The Chicken That Laid Leaden Eggs, And Other Horror Stories.” In this week's post, I seek to drive home an additional point that I may not have made in the earlier post. That point is the fact that urban homesteading, and particularly urban agriculture, have a disruptive effect on the official global food system, because they result in people breaking free of that system. Therefore it is no surprise that the masters of that system might find it advantageous to try to arouse fear of potential “dangers” of urban food gardening, in order to keep people dependent on the official system.

A recent case in point involves keeping urban chickens for the purpose of eating their eggs. An article appeared in a local newspaper warning urban chicken-keepers of the danger of eating eggs from chickens that have ingested lead-based paint from older buildings. That concern is valid, yet the article went on to imply that because of the ubiquitousness of lead in urban environments, it is largely unsafe for people to raise chickens for food in the city. While the article caused many people to get their property and their children tested for lead contamination, these people then concluded that if there were elevated lead levels on their property and elevated blood lead levels in their children, it had to be due to the children eating eggs from contaminated urban chickens.

Now I believe that the writer of the news article had the best interests of readers at heart. Yet the conclusion of that article and the conclusions drawn by some of its readers seem like “fuzzy” logic to me. I think that before we start blaming urban chickens for childhood lead poisoning, we need to conduct some rigorous experiments, including measuring the lead content of random samples of store-bought eggs, double-blind experiments in which blood lead levels of urban gardeners/chicken keepers are measured against levels of non-gardening urban dwellers, and tissue/egg lead levels of chickens who do not ingest lead paint chips, yet are raised in urban environments. Only after such experiments are performed will we be able to blame or exonerate urban chicken-keeping as a source of lead poisoning. In the meantime, I'm still working on my coop. My plan is to get some chicks in July.

As to the problem of reclaiming brownfields for urban agriculture, I applaud all who are tackling this problem – including the solitary backyard tinkerers doing homegrown research. In finding solutions, you are proving yourselves to be true heroes and heroines.


1 comment:

gaiasdaughter said...

Paul Stamets has been experimenting with fungi as soil decontaminents, a process he calls mycoredmediation.

Another option is to build a keyhole garden. These gardens have been hugely successful in Lesotho where growing conditions are harsh, soils are poor and rocky. This method could be adapted to urban gardens where soil contamination and limited space are a problem.