The effect of culture medium on metal toxicity to the marine diatom Nitzschia closterium and the freshwater green alga Chlorella pyrenoidosa

Abstract

The composition of the culture medium and its effects on the toxicity of ionic copper and zinc to the marine diatom Nitszchia closterium and the toxicity of copper and lead to the freshwater green alga Chlorella pyrenoidosa were examined. The inhibitory concentration of copper giving 50% reduction in cell division rate in C. pyrenoidosa increased from 16 μg Cu l −1 in synthetic softwater and 24 μg Cu l −1 in EPA-AAP medium (minus EDTA) to >200 μg Cu l −1 in high nutrient MBL medium. Similarly, marine medium f reduced copper and zinc toxicity to N. closterium 10–20 fold compared to seawater. To overcome the problems of metal complexation by chelators such as silicate, iron and EDTA in the assay medium, unsupplemented seawater and buffered synthetic softwater, enriched only with nitrate and phosphate, have been used for the study of metal toxicities to marine and freshwater algae. These low nutrient media are sufficient to support algal growth over the 4-day assay period.