Meeting Abstract
2,4-dichlorophenoxyacetic acid (2,4-D) is the active ingredient in many systemic herbicides used worldwide for selective weed control and eradication of invasive plants in agriculture and aquatic ecosystems; however, there is limited knowledge of its sublethal toxicity toward non-target organisms. Application practices of 2,4-D herbicides typically coincide with yearly freshwater fish spawning periods and because 2,4-D has been cited as an endocrine disrupting chemical, it is critical to understand how 2,4-D impacts fish offspring throughout their vulnerable development. Therefore, we tested the hypothesis that 2,4-D disrupts the normal functioning of the corticosteroid stress axis. We continuously exposed fathead minnows (Pimephales promelas) from fertilization through 8 weeks to environmentally relevant 2,4-D concentrations (0-2ppm) in DMA4®IVM (DMA4), a commercial formulation applied in the field. After 8 weeks of exposure, we did not observe any impacts on whole-body baseline cortisol concentrations for all treatment groups as compared to controls. In all treatment groups following a stress challenge (momentary removal from water), whole-body cortisol levels increased and peaked at 30 min, started a decline by 45 min, and returned to baseline by 180 min. However, fish exposed to 2,4-D had significantly lower whole-body peak cortisol concentrations as compared to controls at 30 min. The effects of 2,4-D exposure followed an inverse dose-response; exposure to 0ppm (control) peaked at 78ng/g, 0.05ppm peaked at 32 ng/g (p<0.0001), 0.50ppm peaked at 54ng/g (p<0.001) and 2.00ppm peaked at 64ng/g (p>0.05). The results indicate that the corticosteroid stress axis is a target for endocrine disruption by ecologically relevant concentrations of DMA4. Work supported by the WI Dept. of Natural Resources.
