First report on the toxicity of copper and zinc on the Afrotropical whirligig beetle, Orectogyrus alluaudi (Coleoptera: Gyrinidae): Effect on survival and oxidative stress

Abstract

Freshwater whirligig beetles are important macroinvertebrates that help maintain freshwater quality by removing dead insects from the surfaces of lakes, ponds, or streams. In this study, we investigated the response of the whirligig beetle, Orectogyrus alluaudi to copper (Cu) and zinc (Zn) by assessing their survival and biochemical responses after 7 days of the whirligig beetle exposure to the metals. Copper significantly reduced the survival of the beetles with LC50 (median lethal concentration) of 223–100 mg L− 1 at 24 to 168 hours of exposure. However, the LC50 of Zn was only significant at 72 h (482 mg L− 1) to 168 h (150 mg L− 1). Copper, at the lowest exposure concentration of 15 mg L− 1, induced oxidative stress on the beetles by significantly increasing the level of malondialdehyde [MDA], a biomarker of lipid peroxidation. There was also significant glutathione [GSH] reduction at the low Cu concentration. However, Zn had no significant effect on the oxidative stress response of the beetles. This study showed that O. alluaudi is less sensitive to copper and zinc via dermal exposure routes than other aquatic invertebrates. Therefore, an alternative way of exposure via the ingestion of contaminated food might be an important exposure pathway to assess the toxicity of metals on the beetles.