PARENT SESSION
PM25 - Agrochemicals
Monday, 18 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P439) Relationship Between Uptake Capacity and Differential Toxicity of the Herbicide Atrazine in Selected Microalgal Species.

Weiner, Jeannette^*,1,2, DeLorenzo, Marie², Fulton, Michael², ¹ Medical Unviersity of South Carolina, Charleston, SC, US² NOAA/National Ocean Service/CCEHBR, Charleston, SC, US

ABSTRACT- Microalgal species vary in their sensitivity to the triazine herbicide, atrazine. Algal sensitivity may be affected by differences in atrazine uptake, algal physiology, or target site(s) sensitivity. The current study examined uptake of atrazine by microalgal species to determine if it can be used to predict algal sensitivity. Standard toxicity tests were performed on five microalgal species, each representing a different division or habitat. Growth rate EC50 values ranged from 32-98 mg/L atrazine. Test species, listed in order of increasing sensitivity, were: Isochrysis galbana, Dunaliella tertiolecta, Phaeodactylum tricornutum, Pseudokirchneriella subcapitata and Synechococcus sp. Each algal species was exposed to ¹⁴C-atrazine at its growth rate EC₅₀ concentration. At five time-points over 96 hours, samples were filtered to collect algae and washed with unlabeled atrazine to displace labeled atrazine loosely absorbed to the cell surface. Replicate samples were not washed with unlabeled atrazine to examine cell surface binding of atrazine. Filters were then treated with sodium hypochlorite to decolorize the sample and tissue solubilizer to release internalized radioactivity. Radioactivity present in cells and growth medium was measured by liquid scintillation counting. The relationship between algal species sensitivity to atrazine and compound uptake, cell dry weight, cell volume and cell surface area was analyzed by linear regression analysis. Results indicate a significant correlation between atrazine uptake and species sensitivity to atrazine (R²=0.5413, p-value=0.0012). Cell size (based on dry weight, biovolume and surface area) was not significantly correlated with atrazine sensitivity. Other factors such as cell cycle, photosynthetic pigment composition, and differences of atrazine binding within the cell are currently being investigated to determine their contribution to algal sensitivity. These results will further our understanding of how microalgal communities are affected by this widely used pesticide.

Key words: atrazine, uptake, algae, sensitivity