By Leimone Waite, Master Gardener
Q. How does smoke from wildfires affect my garden, and are my fruits and vegetables safe to eat after pollution levels reached “very unhealthy” levels over the last week?
A: In the past few years we have been asked this question several times when the air quality has become hazardous and ash accumulates on our vegetable gardens. The short answer is no, there is no significant risk to eating produce from the garden that has been exposed to smoke. Ash can be a little more problematic, but produce is safe to eat if ash is washed off leaves and fruit.
This same question was asked of the Sonoma County Master Gardeners after the devastating fires around Santa Rosa in 2017. They put together a citizen science group to study the effects of smoke and ash on produce and soil after the fires. After the fires, there was concern from the Food and Drug Administration, the California Department of Food and Agriculture and the California Department of Public Health that firefighting chemicals, and chemicals from combustion products such as polycyclic aromatic hydrocarbons (PAHs) and dioxins and other toxic chemicals might contaminate local produce.
During those fires, local gardens and small farm produce were providing significant food security to the region as it was difficult to get supplies in. Concern were that people working in gardens or on small farms might breathe in the toxic chemicals from ash or inhaled smoke, and that plants could potentially absorb the air pollutants directly through their leaves.
There has been research done on the risk of breathing in air pollutants from wildfire smoke, but little research on the risk to human health from ingesting contaminants from smoke and ash on produce.
To answer the question of produce safety after an urban wildfire, the Sonoma County Master Gardeners worked together to take samples from over 25 sites across the county. They used sampling protocol created under advisement by Environmental Health and Food Safety specialists. From each site they took triplicate samples that included washed and unwashed produce to determine if contaminants were present and if the contaminants could be easily washed off the leaves or fruit. Most produce sampled were leafy greens such as kale, lettuce and chard because they have a large surface area directly exposed to air pollution. In total, over 200 samples were taken and frozen for subsequent laboratory analysis.
The study found no detectable levels of toxins, PAHs or dioxins in the produce and stated that there was a “low concern” to eating vegetables and fruits after exposure to ash and smoke. In fact the study went on to state that the benefits of eating leafy greens outweigh any risk.