Effects of Fire Retardant on Water Quality1

Ammonium-based fire retardants are important in managing wildfires, but their use can adversely affect water quality. Their entry, fate, and impact were studied in five forest streams. Initial retardant concentrations in water approached levels which could damage fish, but no distressed fish were found. Concentrations decreased sharply with time after application and distance downstream, and there was no long-term entry. The numbers and kinds of stream insects were not affected. Simulations of retardant dispersal in streams showed fish mortality might occur from zero to more than 10,000 m below the point of chemical entry, depending on application parameters and stream characteristics. Guidelines to minimize adverse impacts from the use of fire retardants are suggested. Chemical fire retardants play an important role in protecting forest resources from destructive fires. Their use has increased steadily since their introduction in the 1930's. Lowden (1962) reported that aerially applied fire retardant use in the U.S. increased from 87,000 liters in 1956 to more than 28 million liters in 1961. During 1970, 64 million liters of fire retardant were applied aerially to forest and rangeland fires (George 1971). USDA Forest Service aerially applied 55 million liters of fire retardant in 1977. More than 71 percent of this use was in California, Oregon, and Washington (Norris and others 1978). Fire retardants have changed since their first introduction. Borate salts, the first retardants, were effective and long-lasting, but were also phytotoxic and soil-sterilants, and are no longer used (Fenton 1959). Bentonite clay in water is not as long-lasting or as effective as alternative materials (Phillips and Miller 1959). Ammonium phosphate, an effective fire retardant marketed in several formulations, is relatively long lasting, nontoxic and easy to apply (Douglas 1974). The ammonium-based fire Presented at the Symposium on Fire and Watershed Management, October 26-28, 1988, Sacramento, California. This is paper 2476 of the Forest Research Laboratory, Oregon State University, Corvallis. Professor and (Courtesy) Associate Professor, Department of Forest Science, Oregon State University, Corvallis, Oreg. retardants as a group account for nearly all chemical retardants used in controlling forest and range fires today. The possible adverse effects of chemical fire retardants on the environment have received relatively little attention, probably because of the importance of these chemicals in fire control and their seemingly innocuous nature. However, even materials of inherent low toxicity can cause adverse environmental effects when organisms are exposed to toxic amounts. Research and development efforts have concentrated primarily on developing effective fire retardants, delivery systems, and strategies for use. As the intensity of fire retardant use increased, incidents of misapplication or adverse environmental effects have begun to appear. There have been several reports of fish kills when retardants were applied directly into streams, but documentation is marginal. Fire retardants are alleged to have killed a number of trout in one stream in California, but the stream soon returned to normal. In 1969, a large number of juvenile salmonids and more than 700 adult salmon were killed in an Alaskan stream. While retardants were used near the river, the specific cause of death of the fish was not determined. Adult salmon entering the river 4 days later exhibited no toxic reaction (Hakala and others 1971). As a result of these incidents, and concerns among resource managers that fire retardants may adversely affect the environment, an ad hoc interagency study committee was formed in 1970 (Borovicka 1974). The objective of the committee was to foster and coordinate research needed to evaluate the environmental safety of chemical fire retardants (primarily their effect on water quality and aquatic organisms). Toxicology research conducted by Fish and Wildlife Service, Bureau of Land Management, and National Marine Fisheries Service established dose-response relationships for use in evaluating the effects on fish of specific levels of fire retardants in streams (Blahm and others 1972; Blahm and Snyder 1973; Borovicka and Blahm 1974; Johnson and Sanders 1977). Forest Service scientists at the Northern Forest Fire Laboratory (Missoula, Mont.) conducted an initial simulation study of retardant distribution in streams (Van Meter and Hardy 1975). The Pacific Northwest Forest and Range Experiment Station studied the behavior of retardant materials in streams, determined their effect on selected aquatic species in their natural habitat and (through simulation) estimated the effects of retardant application on fish mortality in streams of different characters. This paper draws heavily on the USDA Forest Service Gen. Tech. Rep. PSW-109. 1989 79 PNW research effort (Norris and others 1978), and suggests planning for resource managers concerned about minimizing fire retardant impacts on streams. METHODS FOR FIELD STUDY We applied an ammonia-based fire retardant to five streams in Oregon, Idaho, and California (Norris and others 1978). The application crossed a segment of four of the streams and was parallel (to within 3 m) on the fifth (table 1, fig. 1). The pattern of ground level application we used in the field studies (fig. 1B) is a simplified version of the pattern of retardant deposition resulting from operational aerial application (fig. 1A). Stream water samples collected periodically for up to 13 months after application at locations up to 2700 m downstream were analyzed for various forms of nitrogen and phosphorus. Samples of benthos and insect drift were also collected and evaluated for shifts in species diversity and abundance. RESULTS OF FIELD STUDIES Effects of Retardant on Stream Water Chemistry The principal chemical species in the stream the first 24 hours after application were ammonia nitrogen (NH3 + NH + 4) and total phosphorus. Un-ionized ammonia (NH3) is of primary importance because of its potential toxic effects on aquatic species. The amount of NH3 relative to NH + 4 is dependent primarily on pH (Trussel 1972). As the pH increases, the proportion of ammonia nitrogen present as NH3 increases. The phosphorus may be important in downstream eutrophication. After 24 hours, nitrate (No 3) and soluble organic nitrogen are the primary retardant components in the stream. These are transformation products of the diammonium phosphate in the retardant mixture. Both nitrate and soluble organic nitrogen are low in toxicity and are natural components of aquatic ecosystems. Because NH3 is most important, the results in table 2 and figure 2 emphasize ammonia nitrogen (NH3 and NH + 4) or un-ionized ammonia (NH3). Table 1--General characteristics of the study locations and streams Soil and Stream characteristics Stream and Location Climate parent material Vegetation Width Depth Discharge Tohetie High rainfall-Inceptisol Oregon: cool, moist Andic Haplumbrept representing summers, winter Siltstone and Coast Ranges snow rare claystone Lewis Same Same Same Quartz Moderately high Inceptisol Oregon: rainfall--warm, Dystric Cryochrept representing dry summers, occas. Red breccia and Cascade Range winter snows basalt Bannock Warm, dry summers, Mollisol Idaho: winter snowpack Typic Cryoboroll representing Quartz monzonite Intermountain (acid igneous) Region San Dimas Hot, dry summers Alfisol Southern Calif.: warm, moderately Mollic Haploxeralf representing dry winters Metamorphic and areas of heavy acid igneous chaparral Douglas-fir, Sitka spruce Western Hemlock, Alder Salmonberry