The influence of cyanobacterium exudates on copper uptake and toxicity to a tropical freshwater cladoceran

Abstract

Many studies have shown the reduction of metal toxicity in the presence of dissolved organic matter in natural waters; however, possible roles of metal-edible dissolved organic matter complexes as a vehicle of metal entrance into trophic chains have been poorly investigated. In this study copper uptake and toxicity to Ceriodaphnia cornuta Sars in the presence and absence of exudates produced by Anabaena spiroides Klebahn were investigated. Groups of 30 adult C. cornuta individuals were exposed to a range of copper concentration (10 28 –1 0 26 mol L 21 ) during a 24 h period. The “Trimmed Spearmen Karber” method was used to calculate EC50. Copper toxicity was almost 4-fold lower in the presence of 30 mg L 21 of cyanobacterial exudates; without exudates, EC50 was 8.1 � 10 28 mol L 21 , while with exudates it was 3.2 � 10 27 mol L 21 . Total copper concentration in the animals was determined using differential pulse anodic stripping voltammetry and the results showed that, for both treatments, metal accumulated by the organisms was not significantly different from the negative control, except for immobile individuals. The present results suggest that the animals were able to regulate their body copper content.