Influence of organic solvents on the growth of marine microalgae

Ninety-six-hour toxicity tests of five organic solvents (methanol, ethanol, acetone, N,N-dimethylformamide [DMF], and dimethyl sulfoxide [DMSO]) on nine species of marine microalgae (Bacillariophyceae; Skeletonema costatum, and Chaetoceros calcitrans, Prasinophyceae; Tetraselmis tetrathele, Haptophyceae; Isochrysis galbana and Pavlova lutheri, Dinophyceae; Prorocentrum minimum, Raphidophyceae; Heterosigma akashiwo, Euglenophyceae; Eutreptiella sp., Chlorophyceae; Dunaliella tertiolecta) were conducted. For D. tertiolecta, T. tetrathele, I. galbana, and P. lutheri, methanol was the least toxic solvent. For S. costatum, C. calcitrans and Eutreptiella sp., DMSO was the least toxic solvent. For Heterosigma akashiwo, DMF was the least toxic solvent. In general, solvent toxicity was ethanol > methanol or acetone > DMF > DMSO. In relation to sensitivity of the microalgae to solvents, D. tertiolecta and T. tetrathele were lower in sensitivity, and Eutreptiella sp. and H. akashiwo were higher in sensitivity than the other species. The no observed effect concentration (NOEC) of acetone, DMF, and DMSO were higher than for ethanol and methanol. Acetone, DMF, and DMSO were suitable for carrier solvents used in toxicity test of water-insoluble chemicals. Excellent regression between logEC(50) and logNOEC was obtained (logNOEC = 1.09 x logEC(50) - 0.84, R(2) = 0.91). This equation indicated that higher toxicity was higher application factor (EC(50)/NOEC) than lower toxicity. All application factors were higher than 0.1.