- Author: Jeannette E. Warnert
A summer of smoke and ash in many parts of California has raised questions about the safety of produce growing on farms and in the garden, eggs laid by chickens who peck around in ash-laden areas, and remediation needed to safely and effectively grow food in the future.
UC Agriculture and Natural Resources brought together experts who have researched the effects of previous fires' fallout and studied soil contaminants to share their insight in a two-hour webinar now available at Post-fire Soil Safety video.
“The No. 1 health concern during a fire is smoke inhalation, and it's been well documented that wildfire smoke can negatively impact both the heart and the lungs,” said Claire O'Brien, a pharmacology and toxicology doctoral student at UC Davis. “However, the chemicals found in the smoke don't just stay in the air. They can deposit onto plants and into soil and water.”
Although every fire is unique, some generalizations can be drawn from research conducted following previous fires. UC Cooperative Extension food systems advisor Julia Van Soelen Kim detailed a study conducted following the October 2017 wildfires in Sonoma County and across the North Bay.
With the help of UC Master Gardener and community volunteers, the researchers collected over 200 samples of homegrown collard greens, lettuces, kale and chard that were exposed to wildfire smoke and ash. A subset of the samples were analyzed by a private laboratory.
“There was very low concern about chemicals on produce,” Van Soelen Kim said. “No samples had detectable levels of lead, arsenic, mercury or chromium. And that's a huge sigh of relief.” However, analytical results vary by site, site history and by fire event, and few have pre-fire baseline data to compare with.
Van Soelen Kim said basic food-safety practices should be followed when preparing to eat food grown in a home garden, regardless of ash or smoke contamination.
“You should always wash your hands before and after harvesting, and wash your produce in running water to mitigate any kind of potential risk,” she said.
Are backyard chicken eggs safe to eat?
Another study outlined at the webinar used a similar process to determine whether there might be contaminants in the eggs laid by backyard poultry that live and feed in areas exposed to wildfire ash and smoke.
Scientists know from previous research that chickens exposed to lead in their environment can produce eggs with high lead content and that heavy metal content of ash from urban wildfires is higher than from rural wildfire.
“We combined those two pieces of research with what we know that chickens do all day: they peck at the ground for hours on end,” said Todd Kelman, a veterinarian in the School of Veterinary Medicine at UC Davis. “That makes for a pretty good hypothesis that urban wildfire could pose a risk for the production of eggs and poultry that contain heavy metals.”
Kelman and his team put out a call for eggs from backyard poultry and received samples from 344 premises in fire-affected and non-fire-affected areas of California.
Surprisingly, egg samples that contained higher lead levels came from parts of the state that were not directly impacted by ash and smoke.
“Did our data support our hypothesis that proximity to urban wildfire is a driving source for lead in eggs of backyard poultry? The answer is not so much,” Kelman said. “So, is it safe to eat eggs from your backyard poultry? We can't give you a definitive answer to that question. But we do suggest you assess your risk and reduce the risk of contamination.”
Practices that reduce the risk include keeping chickens off the ground, using a chicken feeder that prevents spillage onto the ground and making calcium readily available, for example in the form of oyster shells, because calcium can prevent the absorption of lead. Making sure that chickens are provided uncontaminated water is also an important part of risk reduction.
For confirmation on the safety backyard chickens and their eggs, lab tests for eggs are available for $60 from the California Animal Health and Food Safety Laboratory at UC Davis, or chickens may be submitted to CAHFS for necropsy.
Are soils safe for growing food after a fire?
Fire effects on soil is another consideration in burned areas, said UC Cooperative Extension urban agriculture advisor Rob Bennaton.
“Fires heat topsoil layers. They reduce the amount of living micro-organisms at the site of the burn, and also affect organic matter and nutrients. Ash deposits over time may make soils more alkaline,” he said. “As a result of these combined factors, there are temporary changes in nutrient levels and the capacity for soils to exchange nutrients for optimal plant growth and nutrition.”
With proper land care and management, soils can be remediated over time.
“It won't happen overnight. Soils were developed over millions of years,” he said.
Some ways to improve safety when gardening in fire-affected areas including keeping the soil covered with wood chips or other landscape mulch to reduce airborne soil dust. Use drip irrigation to prevent up splash onto the undersides of growing vegetables. Promote good drainage, especially at the bottom of slopes to prevent the concentration of contaminants.
Lab tests are often needed to determine the soils' post-fire characteristics. “Don't guess, but test,” Bennaton said.
The UC Master Gardener Program can provide technical assistance to help home gardeners find resources for home soil testing, he said.
Resources and information shared during the webinar
Post-fire soil resources and soil testing information
- UCCE publication on Soils in Urban Agriculture with soil testing & sampling information
- The UC ANR Healthy Soils Website, which has many resources worth reviewing.
- Tips for Interpreting Soil Analysis
- UC Master Gardener of Sonoma County 2018 workshop video “Effects of fire on soil”
Post-fire food safety
- Research on produce safety and backyard chicken egg safety after the 2017 wildfires in California is available at Produce Safety after Urban Wildfire. To view a past webinar recording with these research findings, visit Post-fire Food Safety.
- Poultry wildfire resources from the UC Davis School of Veterinary Medicine
- UC Davis School of Veterinary Medicine: "Safety of Backyard Chicken Eggs Post Wildfire" video
- Best Practices for Produce Safety After Fire
- Understanding Risk: A community guide for assessing the potential health impacts of locally grown produce exposed to urban wildfire smoke
Firewise and sustainable home landscaping design in the defensible space zone
- Visit the UC Master Gardener Program of Sonoma County firewise landscaping web page.
- For a recent firewise & sustainable design and maintenance video by the Resilient Landscapes Coalition.
Impact of smoke & ash on plants
- Author: Pamela Kan-Rice
Vice President Glenda Humiston introduced alumni regent-designate Debby Stegura to UC Cooperative Extension staff and their community partners and clientele in Sonoma County on Nov. 15.
After visiting Beretta Dairy, Bayer Farm Park and Gardens, Sheppard Elementary and Stuhlmuller Vineyards, Regent Stegura tweeted:
“Blown away by @ucanr tour of @UCCESonoma work—Beretta Dairy, @UCMasterGarden, @Stuhlmullerwine, @California4H. Saw #kincaidfire reach, how to prepare better for future fires. @ucanr work benefits all of CA. Thank you!”
The retired business litigator and UC Davis alumna was joined on the tour by Anne Shaw, secretary and chief of staff to the regents, and Michael Bedard, UC state government relations legislative director.
Stephanie Larson, UCCE director for Sonoma County, led the tour, which first visited Beretta Dairy.
“It's so nice to have a dairy advisor,” Sonoma County dairy farmer Doug Beretta said, crediting Randi Black, UC Cooperative Extension dairy advisor, with providing the technical assistance he needed to apply for a grant to reduce methane emissions.
Black, who joined UC ANR in 2017, helped four local dairies obtain grants totaling $2.5 million and said the projects propose to reduce emissions by 9,327 metric tons of CO2 equivalent over the next 5 years, which is comparable to removing 2,028 passenger vehicles from the road for a year.
Beretta talked about the work he has done at the dairy, based on UC research, to improve water quality. David Lewis, UCCE director for Marin and Napa counties, noted that similar manure management and water-quality work is being implemented by UCCE clientele in his counties.
Discussing the hardships created by low milk prices in the dairy industry, Beretta said he appreciated UCCE's agricultural ombudsman Karen Giovannini guiding producers who want to sell value-added products through the permitting process.
From the dairy, Stegura and the group met with Mimi Enright, UC Master Gardener Program manager for Sonoma County, UC Master Gardener volunteers and Julia Van Soelen Kim, North Bay food systems advisor at Bayer Farm Park and Gardens.
Collaborating with Bayer Farm, the Master Gardeners have been expanding outreach to Spanish-speaking members of the community. In addition to all of the traditional Master Gardener outreach, the Master Gardeners in Sonoma County have been actively promoting firewise landscaping to help Sonoma County residents better prepare for wildfires. Using UC ANR materials is critical, Enright said, to assure people the recommendations are based on scientific research.
After the wildfires in 2017, Van Soelen Kim and Enright launched a citizen science project with community partners to assess produce safety. Within days of the fire, volunteers collected 200 samples of leafy greens from school, backyard and community gardens. With funding from UC ANR and the Bay Area Air Quality Management District, they expanded testing to soil and partnered with UC Davis researchers to test eggs laid by backyard poultry, and published guidance for produce safety after urban wildfire.
After the Kincade Fire, when growers and gardeners asked if produce grown outdoors was safe to eat, Enright said UCCE Sonoma County could tell them, based on local research, it was safe to eat if consumers removed outer leaves and washed the produce and that the health benefits of eating fresh produce outweigh any trace contamination.
UCCE has been leading a coalition of community partners and government organizations to educate the community on reducing food waste and increasing food recovery. When PG&E announces public safety power shutoffs, they promote composting food that can't be eaten so it doesn't end up in a landfill.
“This kind of service in communities is not as well-known about UC as the campuses,” Humiston commented to the regent.
Across the street from Bayer Farm, Diego Mariscal, 4-H program assistant, has been collaborating with Sheppard Elementary School. It is one of several schools in the county providing 4-H afterschool clubs and other 4-H programs designed to nurture the next generation of Latino leaders. Last spring, Mariscal worked with families to build a 4-H soccer league for elementary school children. Parents, college and high school students were trained by 4-H to teach children teamwork, soccer skills and healthy eating habits. More than 200 new underserved youth participated in 4-H programs in Sonoma County during the 2018-2019 year.
A few of the soccer players, proudly wearing their green 4-H soccer uniforms, told the group what they liked about 4-H. 4-H All Star Corrianna E., who participates in the 4-H teen program, shared her experience in 4-H and expressed gratitude to the program for helping her overcome her shyness to become a strong public speaker. Corrianna's mother, Naomi Edwards, also shared her experience as 4-H Council President for Sonoma County.
When new landowners ask Gorman for advice, he refers them to Steven Swain, UCCE environmental horticulture advisor, who advises small parcel land managers in Sonoma County on managing the land for fire and wildlife. “Without UCCE, where would they turn?” Gorman asked, adding that people from private companies may have recommendations that may not be in best interest of the land.
Larson introduced new UC IPM advisor Cindy Kron, who succeeds recent retiree Lucia Varela. Kron is launching an IR-4 project to study pesticides for olives, which isn't a big enough market to interest private investment in research. She's also monitoring pears for brown marmorated stink bug because early detection is key to controlling the pest. Spotted lanternfly isn't in California yet, but grapes are among its favorite hosts so Kron is working with UC Master Gardener volunteers and other community members to watch for the exotic pest.
The Kincade Fire destroyed fences and scorched the rangeland at Stuhlmuller Vineyards, forcing Gorman to sell the cattle. He showed the group where the fire failed to advance at the fire break created by the lush vineyards. As a result of the Kincade Fire, Gorman wasn't able to sell his petite verdot, chardonnay and cabernet grapes to wineries. To prove to the insurance company that smoke damaged the crop, his crew picked 30 tons of grapes for testing.
During and after the devastating fires in the North Bay, Larson, who is also a UCCE livestock and range management advisor, assisted livestock owners to gain access to their burned properties; this ensured their animals got food and water. She also organized resource meetings for landowners affected by fires, helping them apply for funding from government agencies and insurance companies for animal, forage and facility losses.
Larson also said her new grazing database Match.Graze has been well-received by ranchers and landowners in Sonoma and Marin counties who want to use grazing to reduce fire fuels. Land managers and grazers can sign up at ucanr.edu/matchgraze to hire sheep, goats, cattle and horses to manage fire fuels.
The regent tours in Sonoma Country and Fresno County were coordinated by Anne Megaro, government and community relations director. She is planning future tours for regents at UC South Coast Research and Extension Center and other locations in the spring.
- Author: Stephanie Larson
Good Fire Alliance
Recovery & Resiliency
“Produce Safety After Urban Wildfire” citizen science project
The Northern California fires of October 2017 created poor air quality and distributed toxic air contaminants over the region. Following the fires and the incredible response from local farmers, UCCE Sonoma County embarked on a “Produce Safety After Urban Wildfire” citizen science project to help answer community concerns about whether the safety of local produce might have been impacted by contaminants carried in the smoke and ash from the fire.
With the support of UCCE Sonoma, community members concerned about the impact of toxic smoke on local produce and UCCE Master Gardeners took over 200 samples of leafy greens from 25 gardens and farms across Sonoma County in the immediate aftermath of the fires; in the summer of 2018 the team took soil samples from five of the original sites sampled. Using funding from University of California Agriculture & Natural Resources Division and the Bay Area Air Quality Management District, we had produce and soil samples from five sites most likely to have received deposits of toxic air contaminants from the urban wildfire tested for heavy metals, dioxins and polycyclic aromatic hydrocarbons.
Based on preliminary findings, we hypothesize that produce safety was not significantly affected by the fires and may be mitigated by washing produce. Preliminary analysis was inconclusive but did not indicate a high degree of contamination. Polycyclic aromatic hydrocarbons were inconclusive due to high method reporting limits from our laboratories. Heavy metals were of low concern, with no detection of lead, arsenic, or mercury. Nickel was found in 2 of 8 samples at levels exceeding Proposition 65's No Significant Risk Level but which may be mitigated by washing produce. Dioxins were of some concern with concentrations found above background levels from FDA's Dioxin Monitoring Program, but below NSRL.
- It is important to note that over long periods of time, exposure to these chemical groups at very low levels can still contribute to health impacts, including at levels below what our tests are able to detect.
- Numerous health benefits including cancer risk reduction have been attributed to green leafy vegetables. These benefits may outweigh the additional risk from trace contaminants detected in some produce in this study. Quantitative comparisons will be provided in our final report.
- Some individuals have higher risks and may want to be in communication with their healthcare provider to better understand if they should take extra precautions. Individuals at higher risk may also benefit greatly from the high nutrition in green leafy vegetables and fresh produce.
- Best practices for reducing risk include: wearing a respirator mask during poor air quality; washing produce thoroughly in running water; peeling root vegetables, testing soil regularly; containing and amending contaminated soil through sheet mulching, raised beds, and compost.
- Best practices that enhance protective factors and should also be pursued, such as increasing produce consumption to promote healthy nutrition, improve immunity, and support resilience to chemical exposures.
Over the next few months, we will be completing our final report and creating additional tools for communicating these results to concerned community members. In the Spring of 2019, we will be conducting community workshops. Reports, handouts, workshop materials, and the protocols from the study will be made publicly available for use by communities experiencing wildfire in the future./h3>/h3>/h3>
Local food producers: The recent wildfires are creating dangerous air pollution in our region. The biggest threat to your health is from inhaling the smoke. Protect your lungs by staying indoors whenever possible, and wearing a respirator mask when outdoors. An N95 respiratory is the minimum protection recommended, while a P100 will provide additional protection from petroleum-based chemicals and smaller particles. Employers of outdoor workers should consider adequate protection for their workers, such as limiting the time that employees work outside and providing adequate respiratory protective equipment (see California Code of Regulations Title 8 section 3203, Injury and Illness Prevention Program, and section 5141, Control of Harmful Exposure to Employees).
During the fires in Sonoma County last fall 2017, many local food growers expressed concern about the impact of the wildfire smoke on the food safety of our local produce. Since then, a group of researchers and concerned community members have been investigating this question. The Produce Safety after Urban Wildfire project will be releasing a final report in early 2019. However, due to this current air pollution emergency, we would like to share that the lab results from our
plant samples DO NOT show extensive contamination of produce exposed to wildfire smoke, and our findings suggest a low health risk from ingesting produce exposed to wildfire smoke.
Fresh produce, especially green leafy vegetables, are critical for nutrition and promoting the body's resilience to the health impacts of smoke. To further reduce risk of contamination, wash produce with running water and remove outer leaves or peels and wash hands after harvesting produce or coming in contact with soil and ash.
Some groups are more vulnerable to health impacts from the smoke and should take extra precaution during this time, including children, elders, and people with respiratory and heart conditions. If you are a garden educator working with kids, please consider activities that can be done inside until air quality improves.
We encourage our community to continue supporting our local food system and sharing our online resources with all those concerned, including our publication:
See our Produce Safety after Urban Wildfire for more resources and information.
Sign-up for our google group of community members discussing these issues and sharing strategies./span>