Acute Toxicity of Fire-Retardant and Foam-Suppressant Chemicals to Hyalella azteca (Saussure)
Introduction
Yearly, millions of liters of fire-retardant chemicals are used on a wide array of ecosystems for suppression and control of range and forest fires [1]. These chemicals are often applied in environmentally sensitive areas, which may contain endangered, threatened, or economically significant plant and animal species. Relatively little information is available on the acute toxicity of these chemicals to aquatic life or on their effect on the environment as a whole.
Long-term fire-retardant chemicals and short-term fire-suppressant foams are two general categories of chemicals typically used in fire fighting. Long-term fire-retardant chemicals are typically composed of ammonium sulfate, ammonium phosphate, or polyphosphate with an attapulgite clay thickener such as hydrated magnesium silicate, or diammonium phosphate with a guar gum derivative. Longterm retardants result in the formation of a combustion inhibiting agent on the fuel following evaporation of the carrier. The effectiveness of these salt formulations in retarding combustion depends greatly on the amount of salt deposited per unit of surface area. Salt content is often increased by using highly concentrated solutions that are highly corrosive [2]. Products are formulated with inhibitors such as sodium ferrocyanide and tolyltriazole to control corrosion. They also contain small amounts of ferric oxide or other coloring agents to mark the location of retardant drops (C. Johnson and C. George, personal communication).
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 [2]. Studies have reported the toxicity of the active ammonium salts found in most fire-retardant chemicals [3-6], but there are few reports of studies exposing aquatic animals to actual fire-retardant chemicals [7].
Short-term fire-suppressant foams are typically composed of surfactants and a variety of solvents. Fire-suppressant foams enhance the extinguishing power of water by increased water retention on fuel sources or by 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 [8,9]. Few studies exposing aquatic animals to actual fire-suppressant chemicals have been reported [10].
Based upon the paucity of reported studies concerning fire-retardant chemicals and formulations, it is impossible to ascertain their effect on organisms without additional research. Moreover, the effects of repeated applications of fire-fighting chemicals on aquatic and terrestrial ecosystems are unknown. Fire managers and policy developers need information on the biological effects of fire-control chemicals to ensure that sound decisions are made concerning fire-fighting activities on private, state, and federal lands.
The toxicity of five fire-retardant and foam-suppressant chemicals was determined for Hyalella azteca. The chemicals tested were selected because they are the most common chemicals used to fight forest and rangeland fires and are currently applied to a wide variety of habitats. Tests were conducted with three fire retardants, Fire-Trol GTS-R, Fire-Trol LCG-R, and Phos-Chek D75-F, and two fire-suppressant foams, PhosChek WD-881 and Silv-Ex.
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