PARENT SESSION
PT2 - Endocrine Disruption
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall

(P545) Effects of Atrazine and Chlorothalonil on a sediment dwelling-copepod using a life cycle bioassay .

Bejarano, Adriana^*,1, Chandler, George¹, ¹ University of South Carolina, Columbia, SC, USA

ABSTRACT- The copepod Amphiascus tenuiremis was used to evaluate effects of the herbicide Atrazine (ATR) and the fungicide Chlorothalonil (CHTH). ATR was toxic to stage-I copepodites (C₁ ) and adult copepods only at concentrations close to the solubility limit of ATR (LC₅₀= >1 mg/L). In contrast, CHTH was highly toxic to C₁s (LC₅₀=23.34 g/L; 95%CI= 20.99-27.39) and adult copepods (LC₅₀= 68.076 g/L; 95%CI= 60.369-76.613). Sub-lethal effects were assessed using a novel 96-well microplate life-cycle bioassay. Briefly, C₁s were followed to adulthood in individual wells containing 200 L of test solution with test solution and food renewal every 3^rd day. C₁s were monitored daily and various endpoints recorded. Upon reaching maturation, individual virgin copepods were randomly mated pairwise in wells containing original concentrations. ATR microplates were run for 17d at 0, 2, 20, and 200 g/L (N=60 C₁s /concentration) and CHTH microplates for 14d at 0, 4 and 7 g/L (N=134 C₁s /concentration). C₁s survival in ATR microplates was 95-99%. Sex ratios were 50F:50M for all treatments except for the 2 g/L treatment where the proportion of males was twice that of females. Reproductive success decreased with increase in concentration, being 89.4%, 80% and 76% for the 0 and 2, 20, and 200 g/L respectively. Second brood size in the 200 g/L treatment was significantly reduced by 5 embryos on average compared to controls. C₁s survival in CHTH microplates was >99%. Although reproductive success of mating pairs (50-54/concentration) was similar across treatments (87±0.9%), the number of females producing nonviable embryos (1 to 5) in their first clutch increased from 20% in controls to 36.2±1.5% in all CHTH treatments. This proportion dropped to 5.8±2% across all treatments in subsequent broods. Third brood gravid females from both bioassays were analyzed for 20-Hydroxyecdysone (20HE).

Key words: atrazine, chlorothalonil, copepods, microplate bioassay