Posts Tagged: smoke

Smoke and ash from wildfire may have lingering impacts in food production

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 on YouTube.

“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.

Additional resources and information shared during the webinar include: 

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 on this web page. To view a past webinar recording with these research findings, click this link.
• Poultry wildfire resources from the UC Davis School of Veterinary Medicine:
• 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

• UC Berkeley Botanical Garden blog post on "The Effects of smoke and ash on plants" 

[This article was first published Nov. 3, 2020]

Farmers concerned about crops tainted by wildfire smoke

When wildfires send smoke into farmland, orchards and vineyards, growers are concerned about the impact of the tainted air on their crops, reported Giuseppe Ricapitio in the Union Democrat.

"It's grapes we worry about the most," said Susie Kocher, UC Cooperative Extension forestry and natural resources advisor. "In the past, there have been bad years when there was a lot of smoke where grapes were on the vine and wineries had to produce the smoky wine because of that effect."

The article said grapes are unlike other agricultural products, in that the skins are permeable. Free volatile phenols created by burning wood become part of the grape itself.

"It isn't something you can wash off," said Ron Harms of Yosemite Cellars winery.

After the 2013 Rim Fire, the winery produced a "Rim Fire Blend," which was successful. However, wine drinkers' palettes differ in terms of their smoke sensitivity. "Some people just can't tolerate (smoke flavor) at all," Harms said.

Other agricultural crops may not be impacted by a blanket of smoke, and some may even benefit. Before Europeans settled in California, Native Americans living in the wilderness would set fires to burn understory brush that built up in the forests.

"It's part of the ecological knowledge of native tribes that smoke is good for trees," Kocher said. "That's not a scientifically proven thing. We don't know."

Autumn wildfire set up research on 'smoke taint' in wine

With the value of wine riding on a delicate balance of aroma and flavor, the impact of winegrapes' exposure to smoke from a wildfire could have significant economic consequences. Last fall's Northern California wildfires sent smoke wafting over an experimental vineyard in Napa Valley, giving scientists the opportunity to study the interplay of smoke and wine quality, reported Jeff Quackenbush in the North Bay Business Journal.

"The moment the smoke started, my phone started ringing off the hook," said Anita Olberholster, UC Cooperative Extension viticulture and enology specialist. “I quickly realized how thin the data is I need to base recommendations on.”

The fires near the UC Davis vineyard provided the perfect experimental platform. Olberholster and her research team sprang into action to start a research project on the fly. Remaining grapes on smoke-exposed vines were picked, loads of commercially grown grapes deemed too questionable for commercial wineries were accepted. Over the past five months, small batches of wine were made from the grapes.

“They all have different levels of smoky character,” Olberholster said. “Some on the nose are actually quite pleasant and not smoky, but the aftertaste is the problem. All of them, even if in small amounts, had that ‘old smoke,' ‘ashtray,' ‘new smoke' aftertaste. It all depends on how sensitive you're going to be at it.”

The scientists are now looking for a process that will remove the smoky compounds, as little as possible of anything else.

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