Urban Farming and Soil Testing

In recent years, the ‘Urban Farming’ and ‘Locavore’ movements have taken America by storm. Isn’t it amazing when you visit a local farmers market and they have peaches, or kale or pecans grown within the city limits? Not only do you feel good about eating good food and helping small businesses but you also help reduce the amount of fuel burned to transport that food (1). With more and more people moving to cities, many think urban farming is a sustainable solution to global urbanization (2).

But life isn’t all rainbows and butterflies. Before that patch of land growing overpriced kale in the suburbs was a farm, who knows what was done to that land? Much of urban land today is polluted by heavy metals such as lead and chromium, along with other harmful chemicals such as arsenic. Although there are ways to farm in urban landscapes without using land, it is important to focus on the issues of polluted soil in cities because it impacts urban farmers but also backyard gardeners and fruit foragers.

The two most common toxins found in urban soils are lead and arsenic, and city land contaminated with such toxins is called a brownfield. Brownfields (3) include areas of the city that used to be factories, airports (4) or industrial farms and the soil has been polluted because of those activities.

The most common sources of lead in urban soils are leaded gasoline and leaded paint. Those were used virtually everywhere before they were made illegal, which is why lead pollution can be found both in your backyard and in your local greenbelt. This lead can be absorbed through the skin if you are gardening with bare hands and don’t wash the dirt off correctly. More importantly, lead can be absorbed by plants such as leafy green and root vegetables. The toxins are absorbed by the plants and then are ingested by you. Lead poisoning can affect the brain adversely and cause developmental impairments especially in children (5). Some believe lead poisoning led to the downfall of the Romans. Don’t let it lead to your demise (6).

Arsenic in city soil most commonly comes from the use of pesticides. Lead arsenate was the most commonly used pesticide for orchards in the 20th century which is why even many suburban soils are contaminated8. Arsenic is highly toxic and in high enough concentrations, will prevent plants from growing. Arsenic can also be ingested in the same ways as lead is, in addition to forming water soluble compounds which pollute groundwater. Arsenic poisoning can lead to many horrible things, including cancer and death(7).

In order to ascertain how contaminated your soil is, the best thing to do is to reach out to your local brownfields organization which can help your soil get tested. Our local Austin Brownfields actually offers free soil testing once a year. You just dig up some soil and drop it off. In the map below, we have mapped the results from Austin Brownfields from 2015-2018.

A quick clarification about the map: each data point represents a soil sample tested for either arsenic (yellow) or lead (blue). The size of the circle is proportionate to the amount of each toxin found in the sample. The map is also interactive so you can zoom into areas of interest/ 

Looking at the overall map, it is clear that we have much more data from west of I-35. Lead is concentrated mostly in the city center while arsenic is mostly concentrated outside the city center, especially south of the river. This may be because urban farms were outside the city and leaded paint and gas stations were concentrated in the city center. If you live in Austin, please look at the data points nearest to you to get an idea of what level of contamination you have. Even better–bring a sample of your soil in for testing. 

So what happens if you have lead or arsenic contamination in your soil? Well, if you live in Austin, then you have nature on your side. In order for many of these toxins to become absorbed by plants and then by us, they have to react and dissolve in water. Lead and arsenic are naturally not soluble in water but acidic water will slowly dissolve them. Luckily, Austin and much of Texas has alkaline soil which actually reduces the uptake of lead and arsenic from soil.

If you live in a part of the country with acidic soil or you have extremely high levels of lead and arsenic then your best option is to add a very thick layer of much and ensure that the soil is mildly alkaline. We also recommend avoiding planting leafy greens and root vegetables as they will typically absorb the highest amounts of heavy metals. Fruits are a better option since plants don’t typically accumulate heavy metals in their fruits and seeds.

This article shouldn’t scare you. Instead, it is meant to make you aware of your surroundings and where your food comes from. If you, like me are a fan of the ‘Urban Farming’ and ‘Locavore’ movements then it helps to be aware of things to avoid when eating sustainably.

Additional Reading:

  1. Ari Levaux. “Feeding Remote Places: When the Last Food Mile is the Middle of Nowhere.” https://foodandcity.org/feeding-remote-places/
  2. Jane Black. “Urban Agriculture: Can it Feed Our Cities?” https://foodandcity.org/urban-agriculture-can-feed-cities/
  3. The EPA’s site on Brownfields:  https://www.epa.gov/brownfields 
  4. The US Department of Housing and Urban Development: https://www.huduser.gov/portal/casestudies/study-1152016-1.html
  5. “Lead in Residential Soils: Sources, Testing, and Reducing Exposure”: https://extension.psu.edu/lead-in-residential-soils-sources-testing-and-reducing-exposure
  6. Lenny Bernstein. “Lead Poisoning and the Fall of Rome”: https://www.washingtonpost.com/news/to-your-health/wp/2016/02/17/lead-poisoning-and-the-fall-of-rome/?noredirect=on&utm_term=.a8419540baac
  7. “Ohio Department of Health: Arsenic Contamination in Gardens”: https://www.odh.ohio.gov/-/media/ODH/ASSETS/Files/eh/Chemical-Fact-sheets/005-Aresenic-in-Gardening.pdf?la=en
  8. Murray B. McBride, et al. “Arsenic and Lead Uptake by Vegetable Crops Grown on an Old Orchard Site, Amended with Compost.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4755492/
  9. Austin Brownfields: http://www.austintexas.gov/brownfields

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