Published online by Cambridge University Press: 12 June 2017
Colorimetry, nephelometry, and chlorophyll assays of cultures of Chlamydomonas reinhardtii Dangeard, Chlorella pyrenoidosa Chick., and Scenedesmus quadricauda (Turp.) Bréb. were used as criteria for measuring algae growth. Among the four s-triazines studied, cyprazine appeared to be the most inhibitory to algae growth, followed by atrazine > simazine > cyanazine. Stimulatory effects of cyanazine, simazine, and cyprazine on chlorophyll content of C. reinhardtii and C. pyrenoidosa were also observed. Cyanazine was most stimulatory on both species but simazine also showed stimulation. Cyprazine was stimulatory only to C. reinhardtii at 0.22 μM concentration but apparently was inhibitory to C. pyrenoidosa at the same concentration. In one experiment, atrazine caused a slight stimulation in C. reinhardtii. Averaged over two consecutive experiments, however, atrazine was inhibitory. Chlorophyll content of the algae was found to be the best criterion for determining effect of the chemicals on algae growth. Continuous exposure of C. reinhardtii culture to the highest concentration of each of the four herbicides resulted in selection of algal lines having increased triazine tolerance.