Inhibitory Effects of Heavy Metals on Growth and Photosynthesis of Three Freshwater Microalgae

Abstract

The effects of copper, zinc and cadmium on the growth rates (cell division dayl) and photosynthesis (O2mgh-1 106cells-l) of Microcystis aeruginosa (Cyanophyceae), Scenedesmus quadricauda (Chlorophyceae), and Aulacoseira granulata (Bacillariophyceae) were determined. Then, the effective concentration (EC50) for growth and photosynthesis in each species of microalga was calculated. Of the three heavy metals tested, copper was found to be the most toxic element to the three experimental organisms. M. aeruginosa exhibited higher tolerance while S. quadricauda exhibited higher sensitivity. There were some differences between EC50 for growth and photosynthesis in the three organisms. In copper, EC50 values for growth obtained in the three microalgae were higher than their EC50 values for photosynthesis. In zinc and cadmium, M. aeruginosa and A. granulata showed the same trend but in S. quadricauda, the EC50 value for growth was lower than that for photosynthesis. The growth-photosynthesis response relationship showed that in copper, growth of the three test plants were less inhibited than their photosynthesis at lower exposure levels (0.001-0.1 μgl-1). In zinc and cadmium, a proportional response existed between relative growth rates and relative photosynthesis in all microalgae. © 1994, The Japanese Society of Fisheries Science. All rights reserved.