Aluminium, gallium, and molybdenum toxicity to the tropical marine microalga Isochrysis galbana

There is a shortage of established chronic toxicity test methods for assessing the toxicity of contaminants to tropical marine organisms. The authors tested the suitability of the tropical microalga Isochrysis galbana for use in routine ecotoxicology and assessed the effects of 72-h exposures to copper (Cu, a reference toxicant), aluminium (Al), gallium (Ga), and molybdenum (Mo), key metals of alumina refinery discharge, on the growth of I. galbana at 3 temperatures: 24 degrees C, 28 degrees C, and 31 degrees C. The sensitivity of both I. galbana and the test method was validated by the response to Cu exposure, with 10% and 50% effect concentrations (EC10 and EC50) of 2.5 g/L and 18 g/L, respectively. The EC10 and EC50 values for total Al at 28 degrees C were 640 g/L and 3045 g/L, respectively. The toxicity of both Cu and Al at 24 degrees C and 31 degrees C was similar to that at 28 degrees C. There was no measurable toxicity from dissolved Ga exposures of up to 6000 g/L or exposures to dissolved Mo of up to 9500 g/L. Solubility limits at 28 degrees C for the dissolved fractions (<10 kDa) of Al, Ga, and Mo were approximately 650 g/L Al, >7000 g/L Ga, and >6000 g/L Mo. In test solutions containing >650 g/L total Al, dissolved and precipitated forms of Al were present, with precipitated Al becoming more dominant as total Al increased. The test method proved suitable for routine ecotoxicology, with I. galbana showing sensitivity to Cu but Al, Ga, and Mo exhibiting little to no toxicity to this species. Environ Toxicol Chem 2015;34:1833-1840. (c) 2015 SETAC