Effects of copper oxide nanoparticles on the Chlorella algae in the presence of humic acid

Abstract

Utilization of nano compounds has greatly increased the discharge of these compounds into the environment, and has increased the possible risk to human health and environment. The aim of this study was to investigate the possible toxic effects of copper oxide nanoparticles on the Chlorella algae in the presence of dissolved and surface-bound humic acid. Chlorella cells were left to grow in the culture media containing copper oxide nanoparticles and HA in different treatments. After specified contact times, the number of algae and Reactive Oxygen Species were daily measured. The results showed that the copper oxide nanoparticles and HA (individually) had a concentration-dependent toxicity on Chlorella algae and these compounds with high concentrations increase the amount of intracellular ROS and decrease the growth rate of Chlorella algae. The LC50 of copper oxide nanoparticles and HA was 2.7 mg/l and 25 mg/l respectively. Dissolved HA in mixture with copper oxide nanoparticles intensified the nanotoxicity by reducing the relative growth rate and increasing the reactive oxygen species. The ROS values reached to 315% and 340% in the experiments with 16 mg/l CuONP + 16 mg/l dissolved HA and 16 mg/l CuONP + 32 mg/l dissolved HA (respectively) compared to the blank controls. The relative growth rate scaled up with increasing the HA content of the complexes of CuONP–HA (surface-bound HA).