Reactive oxygen species (ROS) cause oxidative stress at the cellular level. Research shows that this way, amongst others, they inhibit the germination capacity of plants, produce cytotoxins or exert toxic effects on aquatic invertebrates. Environmentally persistent free radicals (EPFR) are potential precursors of ROS because they can react with water to form these radical species. "Therefore, EPFR are associated with harmful effects on the ecosystem and human health," explains Gabriel Sigmund, the lead investigator of the study.
"Our study shows that these environmentally persistent free radicals can be found in large quantities and over a long period of time in fire derived charcoal," reports Sigmund, environmental geoscientist at the Center for Microbiology and Environmental Systems Science (CMESS) at the University of Vienna. In all 60 charcoal samples from ten different fires, the researchers detected EPFR in concentrations that exceeded those typically found in soils by as much as ten to a thousand times. Other than expected, this concentration remained stable for at least five years, as an analysis of charcoal samples showed which were gathered at the same location and over several years after a forest fire. "The more stable the environmentally persistent free radicals are, the more likely it is that they will have an impact on ecosystems over longer periods of time," explains Thilo Hofmann, co-author of the study and head of the research group.
Samples from fires in forest, shrubland and grassland spanning different climates
The researchers collected charcoal samples from fires of diverse intensity in boreal, temperate, subtropical, and tropical climates. They considered forest, shrubland and grassland fires and, thus, also different fuel materials (woods and grasses). The original material and the charring conditions determine the degree of carbonization. Consequently, both indirectly influence the extent to which EPFR are formed and how persistent they are. "The analyses show that the concentration of environmentally persistent free radicals increased with the degree of carbonization," Sigmund reports. Woody fuels favored higher concentrations. For these, the researchers were also able to demonstrate the stability of EPFR over several years. "We assume that woody wildfire derived charcoal is a globally important source of these free radicals and thus potentially also of harmful reactive oxygen species," adds Hofmann.
International collaboration across disciplines
"It is our collaboration with colleagues at Swansea University in the United Kingdom that enables us to make these highly differentiated statements," explains Sigmund. The wildfire experts at Swansea University are conducting global research into the effects of fire on environmental processes such as the carbon cycle and erosion. They have collected charcoal samples from around the world and sent them to Vienna for analysis, along with information on the timing, duration and intensity of the fires. CMESS researchers analyzed the samples in collaboration with Marc Pignitter of the Faculty of Chemistry using electron spin resonance spectroscopy (ESR spectroscopy). ESR spectroscopy made it possible to quantify the environmentally persistent free radicals in the studied material and to identify their adjacent chemical structures.
Questions about consequences for the ecosystem
The study has provided insights, but also raised further questions: The fact that environmentally persistent free radicals occur in such high concentrations and remain stable over several years was surprising. In future studies, the researchers are planning to also assess the consequences this may have for the environment. "To what extent is this a stress factor for microorganisms after a fire? How does it affect an ecosystem? The study is an impetus for further research," reports Sigmund.
G. Sigmund, C. Santín, M. Pignitter, N. Tepe, S. H. Doerr, T. Hofmann, Environmentally persistent free radicals are ubiquitous in wildfire charcoals and remain stable for years. Communications Earth & Environment (2021),
Katie Wollstein (Rangeland Fire Regional Specialist) and Jacob Powell (OSU Agricultural Extension Agent) are hosting a webinar on fire preparedness for farmers and ranchers. Please advertise in venues you feel appropriate. Specifics and registration information is in the attached flyer.
Agricultural Wildfire Refresher Webinar, Wednesday, February 10th, noon to 1:30
This free webinar with OSU Extension will cover wildfire safety and prevention for agricultural operations and small landowners. The Lone Pine Rangeland Fire Protection Association and their partners will discuss their fire prevention plan. In addition, the webinar will feature a roundtable discussion with local fire managers in North Central Oregon on what producers should do when they have a wildfire and how they can collaborate with first responders in suppression efforts. This webinar is one option for producers to attend an annual agricultural wildfire refresher in 2021 to meet Oregon OSHA requirements for producers with employees who engage in fire suppression on their property. Certificates will be available for attendees. Additional requirements are for producers and employees to receive some sort of initial wildfire training, along with having an emergency action plan for medical and fire emergencies, fire prevention plan, and Job Hazard Analysis form. See attached the flyer and click on this link to register: https://beav.es/Jqy
Produce Exposed to Smoke
When assessing the safety of exposed produce, the difficulty is knowing what has been burning. If it is just vegetation smoke then it's probably safe to eat produce after rinsing off the ash (just the same as having a bonfire in your garden), although it might still taste/smell smoky.
If the air pollution has particulate matter from treated timber, tires, non-food grade oils, or anything plastic or chlorinated that burned it may include a mixture of Polycyclic Aromatic Hydrocarbons (PAHs), dioxins, and metals. Exposure to fire retardant may have also occurred.
An unpublished literature review on the health impacts of PAHs from traffic-related air pollution on lettuce grown in urban agriculture found that:
- Some PAHs can be absorbed into plant tissue, and so cannot be simply washed off.
- The health risk from eating these PAHs is a small proportion of the health impact from breathing them, and it is far below the EPA's level of concern for lifetime cancer risk.
- It is possible that the health benefit of eating the vitamins and nutrients in green leafy vegetables might outweigh that negligible negative impact.
- There is not enough research available on the cumulative impacts of air pollution on produce to make any solid conclusions about the health impacts.
Produce Safety after Urban Wildfire study conducted following Oct 2017 fires in Sonoma County.
Fires & Food Safety flyer by USDA FSIS, 2/2013.
Food Safety after Fire by USDA FSIS, 8/2013.
Some technical guidance tip sheets and power points that may be helpful can be found here:
- Soil Sampling, Risk Mapping & Exposure Prevention - Rob Bennaton
- Contaminants in Soils, Data Collection-Interpreting Test results and Minimizing Exposure by Cornell University
- Testing Laboratories in California
- UCCE Soils in Urban Agriculture
- Best Practices for Produce Safety After A Fire
- Produce Safety After a Fire Tool Kit