Toxicological effects of the aquatic herbicide, fluridone, on male water mites (Hydrachnidiae: Arrenurus: Megaluracarus).

The acute toxicities for technical grade fluridone (Sonar™) and the commercial formulation of fluridone (Sonar®AS) were assessed for male water mites (Hydrachnidiae: Arrenurus: Megaluracarus). Signs of toxicity were evaluated by detection of locomotor dysfunction or death after exposure to concentrations of 100,000, 10,000, 1,000, and 100 µg/L of Sonar™ and 10,000, 5,000, 1,000, 100, and 10 µg/L of Sonar®AS in US EPA, moderately hard reconstituted water (MHRW). The median effective concentration (EC50) was 891 and 631 µg/L for Sonar™ at 48 and 96 h and less than 10 µg/L for Sonar®AS at 96 h. Increased duration of exposure to Sonar®AS from 48 to 96 h had a significant effect on increasing the rate of combined morbidity and mortality. At the lowest concentration of Sonar®AS tested, which is half the concentration allowed within 400 m of any functioning potable water intake for human usage, 40% of the mites were adversely affected at 48 h and 70% were affected after 96 h of exposure. This study demonstrates that Sonar®AS is 60-fold more toxic to water mites than the active ingredient alone. At currently acceptable application rates of 90-150 µg/L fluridone, the addition of ingredients classified as inert, as in Sonar®AS, result in an increased risk of adverse effects on populations of male water mites (Arrenurus: Megaluracarus) in aquatic ecosystems.