Role of Exposure Duration in Hydrogen Ion Toxicity to Brook (Salvelinus fontinalis) and Rainbow Trout (Salmo gairdneri)

Abstract

Acidification of streams and rivers associated with rainstorm or snowmelt events is often episodic as are many environmental introductions of toxic substances. We examined the toxicity of continuous or intermittent exposures to sulfuric acid (H+) to brook trout (Salvelinus fontinalis) embryos, alevins, and fry. Acute toxicity tests were conducted with juvenile rainbow trout (Salmo gairdneri). These studies permitted evaluation of key components of intermittent exposures (toxicant concentration, exposure duration, and recovery period) on mortality, reduced growth, and perturbed electrolyte balance. Lethality of H+ markedly changed with developmental stage of brook trout. Resistance of the chorion to H+ penetration probably protected embryonic fish, while hatching and onset of active swimming exacerbated H+ toxicity. Response surface methods demonstrated that between pH 4 and 7, time–concentration relationships for H+ toxicity were greatly influenced by exposure duration and peak concentration but little by length of recovery period. Daily pulses at pH 4 with duration as short 4.5 h produced marked mortality after 90 d. This did not occur after 4–60 d of testing. Whole-body Na+, K+, and Ca2+ concentrations of brook trout were negatively correlated with mean H+ concentrations after 90 d of exposure. Cation depletion appeared to be a more sensitive index of chronic, sublethal H+ toxicity than reduced growth.