New is not always better: Toxicity of novel copper based algaecides to Daphnia magna

In this study, the effects of traditional copper (CuSO₄.5H₂O) and novel copper algaecides (Captain XTR, SeClear and Lake Guard Blue) were tested on Daphnia magna under acute (48 h) and chronic (21 d) exposure scenarios. The EC₅₀ values calculated in the acute tests were between 0.5 and 0.6 mg Cu L⁻¹ for all four compounds. Lake Guard Blue and CuSO₄.5 H₂O were more toxic than SeClear and Captain XTR. During the chronic test, the effects of SeClear (EC₅₀: 0.274 mg Cu L⁻¹) on reproduction and body length were larger than the effects of the other three copper-based algaecides (EC₅₀: 0.436 mg Cu L⁻¹ for CuSO₄.5 H₂O, 0.498 mg Cu L⁻¹ for Captain XTR, and 0.295 mg Cu L⁻¹ for Lake Guard Blue). Captain XTR had the strongest negative effect on body weight, whereas body weight was affected the least by CuSO₄.5 H₂O. The four copper compounds affected the age at first brood significantly, which was delayed by 1.8, 2.0, 2.3 and 3.2 days for Captain XTR, CuSO₄.5H₂O, Lake Guard Blue and SeClear, respectively. Intrinsic rate of population increase was lowest (0.145 d⁻¹) at the highest dosage in the SeClear treatments. Chemical equilibrium modelling revealed that most copper was chelated with EDTA present in the artificial medium used. These combined results indicate that the toxicity of the novel copper algaecide SeClear to D. magna is greater than that of traditional copper algaecide. Prior to each Cu application, tests on the effects of Cu compounds on the organisms being targeted should be done, taking into consideration the water chemistry.