W8 PM Ecotoxicology of Agrochemicals and Pharmaceuticals
Wednesday, 16 November 2005: 1:50 PM - 5:30 PM in 337-338
(STO-1117-840470) Effect of pulse duration and recovery time on the toxicity of imidacloprid to Chrionnomus tentans.
Stoughton, S1, Liber, K1, Culp, J2, Cessna, A, 1 Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan, Canada2 National Water Research Institute, Environment Canada, Fredericton, New Brunswick, Canada
ABSTRACT- Imidacloprid is a relatively new nicotine mimic insecticide that is widely used across North America. Imidacloprid residues are routinely found in surface waters near treated fields following periods of spray drift, surface runoff, or subsurface water flow, yet little is known about the effects of short and environmentally realistic pulse exposures of imidacloprid to aquatic biota. To address these data gaps, experiments were conducted to evaluate the toxicity of imidacloprid to the invertebrate, Chironomus tentans, using the formulated product, Admire® (240 g/L a.i.). The first experiment exposed C. tentans larvae to either constant, press (10 d) or pulse (96 h, followed by 6 d in clean water) exposure regimes. For the press exposure, growth decreased at 2.9 
g/L; there was no effect at 2.9 g/L in the pulse exposure. The next experiment exposed C. tentans to higher concentrations of Admire® for either 24 or 96 h before being transferred to clean water for the remainder of the 10-d test. Larval growth and survival decreased at 4.7 and 13.3 g/L in the 96-h pulse treatment, with no effect at ≤13.4 g/L in the 24-h exposure treatment. Next, C. tentans were exposed for a total of 96 h, with different recovery times between pulses (four 24-h pulses with 24 h in-between, or two 48-h pulses with 72 h in-between), before being transferred to clean water for the remainder (3 d) of the 10 d test. In the 4x24 h treatment, survival decreased at 15.5 g/L and growth decreased at 5.0 and 15.5 g/L, while in the 2x48 h treatment, survival decreased at 5.7 and 15.8 g/L, and growth decreased at 15.8 g/L. Pulse exposures of imidacloprid can inhibit C. tentans larvae survival and growth when concentrations are > 2.9 g/L and pulse duration is longer than 24 h in total.
Key words: imidacloprid, insecticide, chironomus tentans, puse exposure