Toxicity assessment of Cd and Cu on physicochemical parameters of green microalga Scenedesmus quadricauda

Due to immobilization of heavy metals in the environment, it is necessary to evaluate their toxic effects on living cells. In this study, ecotoxicity of Cd and Cu was studied on inhibition of growth, chlorophyll a (Chl a) and chlorophyll b (Chl b), protein thiol groups and changes in bioconcentration factor (BCF). Cadmium toxicity was confirmed to be higher than Cu on Scenedesmus quadricauda. While in the lower concentrations of Cu the specific growth rate (SGR) was increased, in the presence of Cd only inhibition was confirmed. Level of Chl a was decreased more than level of Chl b. Only at low of Cu concentrations up to 0.07 mg L^-1 the specific growth rate and both photosynthetic pigments increased compared to control. We observed a high bioaccumulation of Cd and Cu in the cells through bioconcentration values. We determined a negative correlation between protein thiol groups and the Chl a (r=-0.461, p<0.01) and Chl b (r=-0.416, p<0.01), respectively, in Cu presence that indicates higher consumption of protein thiol groups probably due higher level of oxidative stress in the cells. Although, we did not confirm this significant correlation for cells cultivated in the presence of Cd, we found significant negative correlation between Cd accumulation and Chl a (r=-0.643) or Chl b (r=-0.699), respectively. S. quadricauda could be suitable candidate for bioremediation of contaminated waters (e.g. in algae-bacteria consortium) because has high capacity of Cd and Cu bioaccumulation and still have enough protein thiols to protect against damage of possible higher oxidative stress.