Effects of low, subchronic exposure of 2,4-Dichlorophenoxyacetic acid (2,4-D) and commercial 2,4-D formulations on early life stages of fathead minnows (Pimephales promelas).

Aquatic herbicides are commonly used to control a wide variety of algae and plants, but they also have the potential to contaminate and affect nontarget organisms. However, the impacts of low-level 2,4-dichlorophenoxyacetic acid (2,4-D) herbicide exposure on larval fish are not well understood. We conducted a series of experiments to determine the effects of low concentrations (0.05, 0.50, and 2.00 ppm) of 2 commercial 2,4-D amine salt herbicide formulations (Weedestroy® AM40 [WAM40] and DMA® 4 IVM [DMA4]) and pure 2,4-D on the development and survival of fathead minnows (Pimephales promelas) at various life cycle stages. Larval survival (30 d post hatch [dph]) was decreased following exposure of eggs and larvae to pure 2,4-D (0.50 ppm; p ≤ 0.001), as well as to WAM40 (0.50 and 2.00 ppm; p ≤ 0.001, p ≤ 0.001) and DMA4 (0.50 and 2.00 ppm; p ≤ 0.001, p ≤ 0.001). The results also narrowed the critical window of exposure for effects on survival to the period between fertilization and 14 dph. Development was not negatively altered by any of the compounds tested, although the commercial formulations increased larval total length and mass at 2.00 ppm. Altogether, the results indicate that the use of 2,4-D herbicides for weed control in aquatic ecosystems at current recommended concentrations (<2 ppm whole lake; <4 ppm spot treatment) could present risks to fathead minnow larval survival. Environ Toxicol Chem 2018;37:2550-2559. © 2018 SETAC.