PARENT SESSION
Oral Session #36: Conservation of aquatic systems: Ecology and ecotoxicology. Presiding: R. Lathrop.
Tuesday, August 7, 2001. 1:00 PM to 5:15 PM. Hall of Ideas H.

Ecologically-relevant effects of pesticides on Daphnia magna.

Kashian, Donna¹, Dodson, Stanley¹, ¹

ABSTRACT- Contaminants that affect Daphnia fecundity, growth, and sexual differentiation may have detrimental ecological effects on Daphnid populations. We examined eleven pesticides: 2,4-D, acetochlor, chlorsulfuran, cyanazine, o,p'-DDT, p,p'-DDE, metolachlor, metribuzin, Di-n -butyl phthalate, dimilin and toxaphene. To determine effects on Daphnia growth and reproduction, short and long-term assays were used to test individual compounds at ecologically relevant concentrations ranging between 0.10 and 100 g/L. Short-term assays (6-days) examined pesticide effects on adult female Daphnia and their offspring. Long-term assays examined pesticide effects on Daphnia growth, fecundity, and offspring sex over its lifespan. Pesticide effects on growth, reproduction, and sexual differentiation were apparent. Acetochlor (100 g/L) significantly decreased Daphnia growth rate (p=0.04), and cyanazine (100 g/L) exposure resulted in significantly smaller clutch sizes (p=0.04). Toxaphene (50 g/L) significantly increased the production of male offspring two-fold relative to the controls (p=0.03), with fewer female offspring. In addition, toxaphene significantly decreased the average clutch size from 17 to 13 individuals and adult size by 5% (p=0.01). Thus, toxaphene and cyanazine may affect Daphnia population growth rates, since a reduction in clutch size and an increase in maturation time is likely to result in reduced Daphnia population growth rates. Fewer asexual females in a population as a result of toxaphene exposure may further reduce population growth rates.

KEY WORDS: daphnia, pesticide, reproduction, population