The measurement of growth and response of marine planktonic algae to arsenic

Abstract

Two marine phytoplanktonic algae, Tetraselmis chui Stein and Hymenomonas carterae (Braarud and Fagerland) Braarud, were examined for variations in response to arsenic exposure. To observe the effects on growth, a simple, precise and accurate method was developed to measure growth characteristics. A computer program was devised to simplify algal growth curve analysis. Various algal assay techniques were discussed. Both organisms were exposed to sodium arsenate and sodium arsenite in a defined medium and a natural seawater medium. T. chui and H. cartarae grew in arsenate concentrations as high as 1000 ppm arsenic (As) as arsenate. Increasing arsenate concentrations caused an increasing lag in the growth of T. chui. The effects of arsenite varied depending upon the media. In all cases arsenic appeared to enhance the growth of H. carterae. Sublethal effects on the mobility of the algae were observed. Sodium arsenite caused the loss of motility in both organisms. The effects of arsenate on mobility were more subtle and varied. Use was made of ⁷⁴As-arsenate to follow arsenic accumulation, kinetics, and biotransformation. After two weeks of arsenate exposure T. chui concentrated arsenic between 100-2000 times depending upon the medium and initial arsenic concentration. H. carterae concentrated the arsenic about five times the level of the surrounding medium. An explanation for the low accumulation in H. carterae was discovered after examination of the kinetics of accumulation..