Toxicity of copper and zinc to two strains of Scenedesmus acutus having different sensitivity to chromium

A Cr-tolerant strain of Scenedesmus acutus (Chlorophyceae) was cultured in the presence of different Cu 2+ or Zn 2+ concentrations to evaluate if it was also tolerant to these metals and consequently maintained unaltered its nutritional value for consumer organisms. The evaluation of tolerance was based on culture growth and recovery rates which were compared with those of the wild type. The evaluation of the nutritional value was based on quantitative determinations of dry mass and carbohydrate and protein content. In the presence of Cu concentrations that were toxic to the wild type, the Cr-tolerant strain grew better and, when transferred to metal-free culture medium, resumed growth more quickly. It also maintained fluorescence and unchanged protein levels. This suggests that the Cr-tolerant strain is also less sensitive to copper. However, no evidence of a lower sensitivity to zinc was found.