Date of this Version
The documented presence of atrazine in surface waters has prompted a large number of studies on its potential adverse effects on nontarget organisms such as freshwater algae, which are the most important primary producers in aquatic habitats and are potential indicators of water quality (Blaise 1993). Recently, a comprehensive database of the ecological effects of atrazine, including 85 freshwater organisms, was compiled (Solomon et al. 1996). Based on this compilation of acute ( ≤ 4 day) or chronic (> 9 day) toxicity values, algae are the most susceptible aquatic organisms to atrazine, although it is apparent that different species and divisions of freshwater algae exhibit varying levels of response to atrazine exposure. Numerous studies have indicated that atrazine inhibits growth and photosynthesis of freshwater algae and algal responses to atrazine vary widely depending upon concentrations used, duration of exposure, and algal species tested. However, there are few studies that directly compare the effects of atrazine between different divisions of freshwater algae, and most studies have focused on short-term (up to 96 hrs and 7 days) growth inhibition with a limited number algal species (Larsen et al. 1986, Walsh et al. 1987, Hersh and Crumpton 1989, Abou-Waly et al. 1991, Kasai et al. 1993, Kirby and Sheahan 1994). Very few studies have focused on long-term (over 14 days) toxicity tests (Kirkwood and Fletcher 1970, Johnson 1986, Megharaj et al. 1987, Okay and Morkoc 1994). Atrazine is relatively persistent in water, and its concentrations would not be expected to vary greatly over time, especially in short-term bioassays (Solomon et al. 1996). More recent testing procedures have recognized that, because of the wide range of sensitivity observed, a battery of species is recommended to improve algal toxicity detection and predictability in chemical evaluation (Boutin et al. 1993). Therefore, in the present study eight freshwater algal species from two divisions were chosen and the effects of atrazine on these algae were assessed over 28 days. The objectives of this study were to examine the effects of atrazine on growth of four green algae and four diatoms and to quantify the differences to atrazine exposure between the tolerance levels of these two algal divisions.