Impacts of 2,4‐dichlorophenoxyacetic acid aquatic herbicide formulations on reproduction and development of the fathead minnow (Pimephales promelas)

Abstract

The authors studied the effects of 2 formulations of 2,4-dichlorophenoxyacetic acid, dimethylamine salt (2,4-D) herbicide on fathead minnow reproduction, embryonic development, and larval survival. Groups of reproductively mature fathead minnows were exposed for 28 d to 0.00 ppm, 0.05 ppm, 0.50 ppm, and 2.00 ppm 2,4-D (target) in a flow-through system. Weedestroy® AM40 significantly (p ≤ 0.05) depressed male tubercle presence and significantly increased female gonadosomatic index, and there were statistical trends (0.05 ≤ p ≤ 0.10) for effects on fecundity and hepatic vitellogenin mRNA expression in females and males. The herbicide DMA® 4 IVM also significantly depressed male tubercle presence. Gonads of females exposed to DMA 4 IVM exhibited significantly depressed stage of oocyte maturation, significantly increased severity of oocyte atresia, and a significant presence of an unidentified tissue type. Also, DMA 4 IVM significantly decreased larval survival. It had no impact on hepatic vitellogenin mRNA expression or gonadosomatic index. No significant effects on fertilization, hatchability, or embryonic development were observed in either trial. The formulations tested exhibited different toxicological profiles from pure 2,4-D. These data suggest that the formulations have the potential for endocrine disruption and can exert some degree of chronic toxicity. The present use of 2,4-D formulations in lake management practices and their permitting based on the toxicological profile of 2,4-D pure compound should be reconsidered. Environ Toxicol Chem 2016;35:1478-1488. © 2015 SETAC.

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)

“…Larvae exposed to all 3 concentrations showed a decrease in survival compared with control over the 30‐d exposure (χ 2 = 20.1183, df = 6, p = 0.0026; Figure B). Previously published data (DeQuattro and Karasov ) from our laboratory illustrating a decrease in fathead minnow larval survival after exposure to DMA4 have been included in Figure to allow a direct comparison of WAM40 and DMA4 exposure trials (Figure C). Surviving larvae exposed to WAM40 displayed an increase in both mass and total length at 2.00 ppm concentration (total length: χ 2 = 25.93, p = 0.0002, mass: χ 2 = 29.46, p < 0.0001; Figure A and B).…”

“…Survival (%) is shown as a function of days post hatch ( A ), or at 30 d post hatch ( B ). ( C ) Analogous data for comparison from DeQuattro and Karasov (). Data are mean ± standard error of the mean ( n = 10–12 tanks in each treatment, each with 10 progeny from a pair of exposed adults).…”

“…Another experiment done in our laboratory showed no significant impacts on larval survival when only the parental generation was exposed (constant exposure through spawn) and larvae were hatched and raised to 30 dph unexposed (Supplemental Data, Figure S2). Moreover, neither WAM40 nor DMA4 seem to have immediate negative impacts on the survival of fathead minnow embryos (spawn to hatch) regardless of parental exposure (Supplemental Data, Figure S3; DeQuattro and Karasov ). These data taken together suggest that the larval stage, in particular from fertilization to 14 dph, is a critical window of exposure to 2,4‐D.…”

“…Crucial endocrine systems are under development during early life stages (i.e., the hypothalamic–pituitary–interrenal, hypothalamic–pituitary–thyroid, hypothalamic–pituitary–gonadal axes; Inui et al ; Bogers et al ; Aslop and Vijayan ; Ankley and Johnson ). Adult fathead minnows exposed to DMA4 or WAM40 showed a decrease in tubercle count (DeQuattro and Karasov ), suggesting that 2,4‐D or some other component of those formulations was acting as an antagonist of an androgen receptor–mediated pathway (Ankley et al ). The androgen receptor has been shown to be active early in fish embryos and larvae (Hossain et al ; Gorelick et al ) and can affect a myriad of early life developmental and physiological pathways (Borg ).…”

“…A recent study conducted in our laboratory (DeQuattro and Karasov ) continuously exposed adult fathead minnows (4 wk) and their offspring (from fertilization to 30 d post hatch [dph]) to DMA® 4 IVM (DMA4). The results showed a significant decrease in larval survival at concentrations as low as 0.034 ppm.…”