Growth rate of <i>Scenedesmus acutus</i> in laboratory cultures exposed to diazinon

Abstract

The effects of the pesticide, diazinon on growth rate was examined in unialgal cultures of freshwater green algae, Scenedesmus acutus through 96 h acute toxicity tests. S. acutus was exposed to different concentrations of diazinon (1, 2, 4, 8, 16 and 32 μl) in the laboratory maintained at 23 ± 1°C and 16:8 light : dark regime. Cell numbers were determined daily and growth rates were calculated for a period of 4 days. The growth rate of S. acutus in the control cultures was higher at 0 to 4 days (40.000 to 276600 individuals), but the growth rate of the treated cultures with diazinon decreased at 2 to 4 days (28000 to 10320 individuals). The results demonstrated adverse effects of diazinon on freshwater green algae (S. acutus). Thus, the application of this pesticide for pest control in agriculture must be done carefully since any disturbance affecting algae with similar or higher sensitivity will have severe repercussions on higher trophic levels.

Key words: Acute toxicity, algae, diazinon, growth rate, Scenedesmus acutus.