Concerns over Ecotoxicity of Fire Retardants Can Further Complicate Complex Wildfire Injury Assessments
March 1, 2018
The recent spate of severe wildfires in California has spurred concerns over the environmental and ecological safety of aerially-applied fire retardants, especially to stream ecosystems and water supplies. Fire retardants primarily consist of ammonia- and phosphorous-based compounds, similar to chemical fertilizers, amended with additives to aid in application precision and persistence during firefighting efforts. They are applied to terrestrial habitat at rates of 1 to 8 gal/100ft2 (USFS 2011a).

The toxicity of ammonia-based fire retardants to aquatic species is projected to be low (EPA 2014). Guidance from the United States Forest Service specifies that fire retardants should not be applied aerially within 300 ft of water bodies (USFS 2011b), yet there is concern that drift or accidental application to streams and movement of terrestrially applied retardants into aquatic systems during rain events might harm populations of sensitive fish species, including salmon species.

It is important to consider the potential effects of wildfires on aquatic systems. Stream systems in heavily burned areas exhibit increased temperatures, high turbidity, reduced oxygen levels, and losses of important fish spawning and resting habitat, and these changes can persist for years following a fire (Cooper et al. 2014; Palmquist and Deardorff 2016). The targeted use of fire retardants may be key in reducing the severity of wildfire effects on aquatic systems, and so any risk associated with their use must be weighed against the risk and effects of prolonged burning.

Ultimately, the effects of wildfire or wildfire control efforts on aquatic ecosystems are highly complex, and baseline conditions, including impacts from mining, logging, urbanization, and agriculture, may exacerbate these impacts. Assessing the ecological and water quality impacts of wildfire and wildfire control methods requires a thorough investigation that utilizes a comprehensive understanding of baseline conditions, wildfire severity, retardant use, and subsequent environmental conditions.

How Exponent Can Help

Exponent has multidisciplinary expertise to help you navigate and make sense of these highly complex wildfire relationships and their effects. Our professionals have expertise in conducting ecological injury assessments following large-scale wildfires, taking into account complex baseline conditions. Exponent can model the fate and transport of various chemicals, including fire retardant compounds, and evaluate and advise on water quality impacts and optimization of water treatment following wildfires.


Cooper, S.D., Page, H.M., Wiseman, S.W., Klose, K., Bennett, D., Even, T., ... & Dudley, T. L. 2014. Physicochemical and biological responses of streams to wildfire severity in riparian zones. Freshwater Biology. 59(12), 2600–2619.

EPA., 2014. An Alternatives Assessment for the Flame Retardant Decabromodiphenyl ether (DecaBDE). Design for the Environment.

Palmquist, K., and Deardorff, T.L. 2016. The Effects of Wildfire on Stream Ecosystems in the Western United States: Magnitude, Persistence, and Factors Affecting Recovery. In World Environmental and Water Resources Congress 2016 (pp. 389–396).

USFS. 2011a. Nationwide Aerial Application of Fire Retardant on National Forest System Land. Final Environmental Impact Statement. United States Department of Agriculture, Forest Service, Fire and Aviation Management. Washington, D.C. October 2011.

USFS. 2011b. Nationwide Aerial Application of Fire Retardant on National Forest System Land. Record of Decision. United States Department of Agriculture, Forest Service, Fire and Aviation Management. Washington, D.C. December 2011,

Ecotoxicity of Fire Retardants

Figure 1. Stream exposed by wildfire, subject to warming, reduced oxygenation, and algal blooms

Ecotoxicity of Fire Retardants

Figure 2. Application of fire retardant