lethal effects of tilt and benomyl fungicides on population of green microalgae scenedesmus quadricauda

aquatic environments are often contaminated by various industrial, agricultural and domestic sewage, while different pesticides have markedly different effects on aquatic life. scenedesmus spp. are often used as an indicator to show changes in physico-chemical and environmental conditions of the aquatic ecosystems. this study aimed to investigate the effects of different concentrations of pesticides, fungicides tilt(propiconazole) and benomyl on the population of green algae (scenedesmus quadricauda) and to determine 96 hour ec50 for it. the study was conducted in a completely randomized design at 96 hours with 4 treatment (four levels of pesticide and control)and three replications in medium bbm (bold basal medium) in accordance with o.e.c.d as standard method. the highest mortality rate occurred at 2.5 mg/l and is 28.40 µg/l of fungicides benomyl and tilt, respectively. also, 96 hours ec50 determined 0.834 mg/l for benomyl and 6.612 µg/l for tilt. statistical analysis showed the significant differences in daily growth rate between some concentrations of studied toxin, as the cell density decreased with increasing toxin consebtration. overall results indicated that fungicide benomyl with degree of toxicity very high toxicity(dangerous) existing in the water bodies has an influencing effect on cell destruction of green algae (s. quadricauda). also the results suggested using such species (s. quadricauda) as an indicator for biomonitoring of aquatic ecosystems because of its rapid response to contaminants.