Acute Toxicity of Fire Control Chemicals to Daphnia magna (Straus) and Selenastrum capricornutum (Printz)
Introduction
In 1992, approximately 91 million liters of ammonia-based long-term fire retardant chemicals were used on a wide array of ecosystems for suppression and control of range and forest fires in the United States (C. Johnson, U.S. Forest Service, personal communication, 1993). These chemicals are often applied in relatively undisturbed areas, which may contain endangered, threatened, or economically significant plant and animal species. Two types of chemicals are typically used in fire control: long-term, non-foam fire retardant chemicals and short-term foam fire suppressant chemicals. Little information is available on the toxicity of these chemicals to aquatic life or their effect on the environment.
Long-term non-foam fire retardant chemicals are typically composed of ammonium polyphosphate with an attapulgite clay thickener (hydrated magnesium silicate) or combinations of ammonium sulfate, ammonium phosphate, or diammonium phosphate with a guar gum derivative thickener. Long-term retardants result in the formation of a combustion inhibiting agent on the fuel following evaporation of the carrier. The effectiveness of these ammonia salt formulations in retarding combustion depends greatly on the concentration of salt deposited per unit surface area. Concentrated fire retardant solutions are highly corrosive, and often contain corrosion inhibitor chemicals such as sodium dichromate or sodium fluorosilicate. Small quantities of coloring agents such as ferric oxide are added to mark the location of retardant drops (Dodge, 1970).
Although the extensively used ammonium compounds are essentially fertilizer formulations and are thought to have minimal toxicological or ecological impact, fish kills have occurred in streams accidentally contaminated by fire retardant chemicals (Dodge, 1970). Almost complete mortality of trout was reported in a section of the Little Firehole River due to a fire retardant drop during the major fire in Yellowstone National Park in 1988 (Minshall and Brock, 1991). Studies have been reported on the toxicity to fish of the active ammonium salts found in most fire retardant chemicals (Singh et al., 1985; Ram and Sathyanesan, 1986; Sheehan and Lewis, 1986; Pramanik and Sarkar, 1987), but there are few reports of studies exposing fish to actual fire retardant chemicals (Johnson and Sanders, 1977). Norris et al. (1978) identified the need to assess the toxicity of fire retardants to aquatic invertebrates, but that research has been the topic of only one project and it tested fire retardant chemicals that are no longer manufactured, but that contained the same major components as current chemicals (Johnson and Sanders, 1977).
The use of foam suppressants in fire fighting is becoming more prevalent because the amount of water required in fire fighting can be reduced by over 60% (Schlobohm and Rochna, 1988). Short-term fire suppressant foam chemicals are typically composed of surfactants and a variety of solvents. Foam suppressants enhance the extinguishing power of water by increased water retention on fuel sources or reduced evaporation or both. The surfactant portion of foam suppressants has been studied and was determined to be detrimental to aquatic life because it decreases water tension, thereby decreasing the aquatic organism's ability to obtain life-sustaining oxygen. Few studies exposing aquatic animals to actual fire suppressant chemicals have been reported (Norecol, 1989).
Based upon the paucity of reported studies concerning fire retardant chemicals and formulations, it is difficult to ascertain their effect on organisms without additional research. Moreover, the effects of repeated applications on aquatic and terrestrial ecosystems are unknown. Information is needed on the biological effects of fire control chemicals by fire managers and policy developers to ensure that sound decisions are made concerning fire-fighting activities on private, state, and federal lands.
The toxicity of three non-foam retardent and two foam suppressant chemicals was determined for Daphnia magna and Selenastrum capricornutum. The organisms were chosen based on the role each species plays in the aquatic ecosystem. Daphnids are a water column organism feeding on primary producers such as algae and bacteria, whereas algae are at the base of the aquatic food web. Studies were conducted with non-foam retardants Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D75-F, and foam suppressants Phos-Chek WD-881 and Silv-Ex. The chemicals tested were selected because they represent the range of chemicals commonly used to fight forest fires in a wide variety of habitats.
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