SPECIATION OF COPPER IN RELATION TO ITS BIOAVAILABILITY

Copper speciation and bioavailability for Scenedesmus quadricauda has been studied in natural waters and in synthetic culture media. Other elements were studied simultaneously. When phosphorus and nitrogen limitation were excluded by adding these elements, copper was limiting algal growth in some natural waters. In the toxic range, growth inhibition by copper was highly correlated with copper detected by electrochemical methods and with calculated free copper. Copper was toxic to S. quadricauda when free copper concentrations roughly exceeded 10(-10.5) M, and was limiting for values somewhere lower than 10(-12.5) M. Because we found copper limitation in some natural water samples, free copper concentration in those water samples therefore must have been lower than 10(-12.5) M. The hypothesis that the free metal concentration rather than the total concentration determines bioavailability was confirmed for copper, cobalt and zinc.