Eco-tip: Is food from your garden safe after a wildfire?

In addition to the tragedy experienced by many whose homes burned in local fires in recent years, many homes were, like mine, damaged but not entirely burned down by the fires.

After the Thomas Fire, an insurance company funded extensive repair and cleaning of my house, but there was no cleaning of the soil. I grow vegetables in raised beds, herbs in pots and fruit trees on a slope.

I replaced burned trees with new ones and replaced burned irrigation lines in the raised beds and herb pots, but I wondered whether my soil was safe.

A free workshop on post-fire food safety will be offered this Thursday from 1-4 p.m. at the Crowne Plaza Hotel in Ventura. Although the workshop is free, registration is required at https://ucanr.edu/survey/survey.cfm?surveynumber=29016. For more information about the program, see ceventura.ucanr.edu

Ben Faber, a Ventura-based farm adviser with the University of California Cooperative Extension, is helping organize the workshop. He shared some of the questions he has received over the past two years, which will be addressed at the workshop:

• What are the effects of fire and smoke and ash and heat and all the other potential things that might affect plants and animal products that we eat?
• Can you simply wash off contaminants?
• What is the impact on the soil itself?
• Does anything special need to be done to start producing food again?

Faber listed several laboratories able to test soil for heavy metals and volatile organic compounds. Although laboratories do not interpret results, you can use lab-generated data to consult with experts who will help you make decisions about potential remediation measures.

One of these labs is Fruit Growers Laboratory in Santa Paula. Glenn Olsen, marketing director there, said his company has helped dozens of people statewide, including from the fire-devastated community of Paradise, test their soil for CAM 17 heavy metals.

The list of CAM 17 heavy metals is derived from the California Administrative Manual and the California Code of Regulations. It was used by contractors working for the California Department of Resources Recycling and Recovery to help ensure soil was safe after clearance of lots where homes burned.

How to get your soil tested

Fruit Growers Laboratory usually charges $315 to test a sample, which is typically collected in an 8-ounce glass jar. The lab discounts this rate to $250 for fire victims.

Testing varies depending on soil conditions, exposure to fire hazards, watering practices and other factors, but Olsen described a suggested sampling protocol for planter beds or cultivated areas. Residents collect a composite sample, assembled from five small grabs from different locations in an area of concern. Digging down 3 to 6 inches or to the root depth of your plantings may give you more information about the soil available to plants, but subsurface soil most likely will yield only answers about pre-fire background levels. Samples from the surface, in undisturbed areas, will reveal more about the effects of fire.

Mix these samples in a bucket, and then fill the jar and send the composite sample to a laboratory.

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Separate samples are needed, and may be collected in the same way, if customers also want an EPA 524 test, which searches for the presence of more than 60 volatile organic compounds that may be in soil after a nearby structure fire or from melted PVC pipes or underground lines. If customers want to test for VOCs, EPA Method 8260 analyzes for more than 90 compounds. Fruit Growers Laboratory charges $265 for this test.

Unfortunately, even if a homeowner is diligent enough to collect samples, send them to a lab and pay for testing, Olsen acknowledges it is unknown how much uptake into the roots will result from the presence of contaminants.

“Variables, such as sun exposure, soil, plant type, soil condition, amendments, watering and slope affect potential rate of uptake,” according to Olsen.

What about asbestos?

In addition to concern about heavy metals and volatile organic compounds, some people with gardens adjacent to burned structures have concerns about the potential for asbestos fibers in their soil.

Ed Cahill, vice president of the asbestos division for EMSL Laboratories, noted that houses built between 1930 and 1980 may have asbestos-containing building materials in items such as insulation, textured paints, patching compounds, ceiling joints and floor tiles.

According to Cahill, “If a house has burned down, asbestos may end up in the surrounding soil, deposited from the fire plume” or by dust generated by demolition or hauling of burned debris.

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The primary concern is breathing in asbestos fibers when the soil is disturbed. 

In addition to testing for metals and volatile organic compounds, EMSL, also known as LA Testing, performs qualitative or quantitative tests for asbestos. However, like testing for metals and volatile organics, resulting data may not provide clear answers about the level of danger.

Cahill pointed to some actions to mitigate the risk of exposure, such as replacing soil in small beds, planting thick vegetation or adding mulch to large areas to minimize wind erosion. Short-term exposure can be minimized by moistening the ground to avoid dust before gardening.

Eco-Tip is written by David Goldstein, an environmental resource analyst for the Ventura County Public Works Agency. He can be reached at 658-4312 or david.goldstein@ventura.org.