Toxicity of Wildland Fire-Fighting Chemicals in Pulsed Exposures to Rainbow Trout and Fathead Minnows.

Intrusions of fire-fighting chemicals in streams can result from containment and suppression of wildfires and may be harmful to native biota. We investigated the toxicity of seven current-use fire-fighting chemicals to juvenile rainbow trout (Oncorhynchus mykiss) and fathead minnows (Pimephales promelas) by simulating chemical intrusions under variable field conditions to provide insights into the potential damage these chemicals may cause in waterways. In three separate attenuated exsposure assays in which chemical concentration decreased throughout the 96-h exposure period, we varied water flow rate, water hardness, and initial concentration of test chemical. In an additional series of four pulsed exposure assays in which fish encounter chemical for up to 1 h followed by an observation period in control water, we altered concentration of test chemical, water temperature, duration of chemical exposure, and number of exposures to determine delayed toxicity or recovery. Mortality of rainbow trout was higher across treatments at a warmer temperature and also increased with increasing concentration rate, increasing exposure duration, and sequential exposures across assays. For fathead minnows, mortality increased with increasing concentration of fire retardant and longer exposure durations. Because the ratio of toxic un-ionized ammonia to ionized ammonia is greater with increasing temperature and pH, future studies could investigate the effects of water temperature and pH on native fishes under environmentally relevant concentrations of fire-fighting chemicals. Environ Toxicol Chem 2022;41:1711-1720. Published 2022. This article is a U.S. Government work and is in the public domain in the USA.