John Wiley & Sons, Ltd.

Toxic effects of combined stressors on Daphnia pulex: Interactions between diazinon, 4‐nonylphenol, and wastewater effluent

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Contaminant exposure in aqueous systems typically involve complex chemical mixtures. Given the large number of compounds present in the environment, it is critical to rapidly identify hazardous chemical interactions. This study utilizes a prototype for a novel high throughput assay to quantify behavioral changes over time to identify chemical interactions that affect toxicity. The independent and combined effects of two chemicals, diazinon (an insecticide) and 4‐nonylphenol (a detergent metabolite) on the swimming behavior of the freshwater crustacean, Daphnia pulex were examined. Cumulative distance and change in direction were measured repeatedly via optical tracking over 90‐minutes. Exposure to low concentrations of diazinon (0.125 to 2 µM) or 4‐nonylphenol (0.25 to 4µM) elicited significant concentration‐ and time‐dependent effects on swimming behavior. Exposure to 0.5 µM 4‐nonylphenol alone did not significantly alter mean cumulative distance, but did elicit a small, significant increase in mean angle, the measure of change in direction. When 0.5 µM 4‐nonylphenol was used in combination with diazinon (0.125 to 0.5 µM) it augmented the adverse impact of diazinon on the swimming behavior of Daphnia. Additionally, enhanced sensitivity to diazinon was observed in animals exposed to treated wastewater effluent for 24 hours prior to a diazinon challenge. These experiments demonstrate that exposure to 4‐nonylphenol and complex chemical mixtures (e.g. treated wastewater), can enhance the toxicity of exposure to the insecticide diazinon. This article is protected by copyright. All rights reserved

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