Acute and subchronic toxicity of methylene blue to larval fathead minnows (Pimephales promelas): Implications for aquatic toxicity testing

Abstract

AbstractThe acute and 7‐d subchronic toxicity of methylene blue were determined for fathead minnow larvae using U.S. Environmental Protection Agency methods. The 96‐h lethal concentration (LC50) was 45 and 15 mg/L at 20 and 25°C, respectively. The 7‐d chronic value for survival under laboratory light and low light was the same (2.1 mg/L). However, under laboratory light, larval growth was impaired at lower concentrations (chronic value = 0.6 mg/L) than under low light (chronic value = 2.1 mg/L). To assess prior methylene blue treatment on larval sensitivity, embryos, larvae <24 h old, and embryos followed by larvae were treated with 3 mg/L methylene blue. Cadmium LC50 values were similar between methylene blue‐treated and untreated control groups. When larvae treated with methylene blue as embryos were subchronically exposed to an effluent, survival was similar to that of the untreated group. However, dry weight of the treated larvae was significantly lower. Differences in dry weight between treated and untreated groups were reduced as the age of the larvae at test initiation increased. Treatment of incubating embryos using 3 mg/L methylene blue does not appear to affect larvae sensitivity to cadmium but may affect the growth of larvae used in subchronic testing.