| High concentrations of the steroid hormone progesterone (P4; 375 ng/L) and androstenedione (A4; 300 ng/L) were measured in snowmelt runoff associated with large livestock feeding operations in Wisconsin. On average, 4.6 million pounds of 2,4-dichlorophenoxyacetic acid (2,4-D) herbicides are applied annually in the U.S. The effects of singular exposure to P4, A4, and 2,4-D herbicides (Weedestroy AM40RTM and DMA4RTM IVM) on the reproduction and development of the fathead minnow were studied. A fish short-term reproduction assay (FSTRA), an embryonic development assay, and a larval exposure assay were used. Endpoints throughout the work included: fecundity, fertilization success, hatchability, tubercle scores, gonadosomatic index (GSI), hepatic vitellogenin (Vtg) mRNA expression, embryonic development, hatch success, gonad staging, oocyte atresia, and larval survival. P4 caused dose-dependent decreases in fecundity and fertility, significantly reduced GSI, and reduced Vtg induction in females. There were no effects of P4 on embryonic development or hatching success. In males, A4 significantly increased Vtg mRNA expression (an estrogenic effect), significantly reduced GSI, and had no significant effect on tubercle presence. In females, A4 induced tubercle (an androgenic effect) with no significant effects on fecundity, fertilization, GSI, embryonic development, or hatchability. WeedestroyRTM AM40 significantly depressed male tubercle presence and significantly increased female GSI, and there were statistical trends for effects on fecundity and hepatic Vtg mRNA expression. DMARTM 4 IVM also significantly depressed male tubercle presence. Gonads of females exposed to DMARTM 4 IVM exhibited significantly depressed stage of oocyte maturation, significantly increased severity of oocyte atresia, and a significant occurrence of an unidentified tissue type. DMARTM 4 IVM significantly decreased larval survival. DMA4 had no significant impact on fecundity, hepatic Vtg mRNA expression, or GSI. No significant effects on fertilization, hatchability, or embryonic development were observed in either 2,4-D trial. Formulations exhibited different toxicological profiles than pure 2,4-D. Exogenous P4 and A4, as well as 2,4-D formulations should be considered endocrine active. 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. |
