Fathead Minnow Lifecycle Tests for Detection of Endocrine-Disrupting Substances in Effluents

Abstract

The goal of this study was to assess the responses of fathead minnows (FHM) exposed to known endocrine-disrupting substances (EDS) in our labs. As well, we wanted to examine the applicability and sensitivity of the full lifecycle FHM test for use on-site, exposing fish to a complex environmentally relevant Canadian effluent. Fathead minnows exposed from the egg stage to ethinylestradiol (EE2, 0-32 ng/L) or methyltestosterone (MT, 0-3200 ng/L) had decreased growth (length, weight) at high concentrations. Development of secondary sex characteristics was a sensitive indicator of exposure to androgen and estrogen. Fish exposed to MT showed premature male sex characteristics such as nuptial tubercles by 30 days post-hatch (dph). These changes were more dramatic in older fish (at 60 and 90 dph), which showed premature male sex characteristics at very low MT concentrations (100 ng/L). Fish exposed to 3.2 ng/L EE2 had premature development of ovipositors at 60 dph. As well, exposure to very high MT concentrations (1000 and 3200 ng/L) caused development of ovipositors after 60 days (but not at 20 and 30 dph), presumably due to aromatization of MT to methylestradiol (as suggested by other researchers). The fathead minnow lifecycle assay, tested with a known estrogen and androgen, proved to be useful for detection of EDS-related changes caused by a real-life effluent mixture. Lifecycle exposures of fathead minnow eggs to bleached sulphite mill effluent (BSME) showed changes in secondary sex characteristics and growth. In contrast to EE2 and MT, fish exposed to BSME had increased growth. Changes in secondary sex characteristics of fish were seen in both male and female minnows exposed to BSME, but there was an overall shift towards increasing numbers of female fish (based on external sex). The full lifecycle assay provides a definitive test for reproductive/EDS effects, and it appears that some of the most sensitive endpoints we studied were the premature development of secondary sex characteristics.

Effects of model aromatizable (17α-methyltestosterone) and non-aromatizable (5α-dihydrotestosterone) androgens on the adult mummichog (Fundulus heteroclitus) in a short-term reproductive endocrine bioassay

“…Simultaneous estrogenic and androgenic effects have been reported (Ankley et al, 2000;Parrott and Wood, 2002) and are attributed to the successful aromatization of MT to 17α-methylestradiol (ME 2 ; Simpson et al, 1994). Increased plasma ME 2 levels have been reported in fathead minnow (Pimephales promelas) exposed to MT for seven days (Hornung et al, 2004), with estrogenic effects being due to ME 2 synthesis.…”

Assessing Effects of Metal Mining Effluent on Fathead Minnow (Pimephales promelas) Reproduction in a Trophic-Transfer Exposure System

“…However, all applications of this approach to date have used water-borne exposures (9). Furthermore, many bioassays employed to assess the effects of complex sewage, mining, and pulp mill effluents (fathead minnow life cycle and partial life cycle bioassays) are conducted using water-borne exposures (15) and ignoring the potential contribution of trophic transfer as a significant route of exposure.…”

Effects of 17α-ethynylestradiol on early-life development, sex differentiation and vitellogenin induction in mummichog (Fundulus heteroclitus)

“…Medaka eggs injected with EE 2 have shown sex reversal of genetic males upon growout (Papoulias et al, 1999) while medaka exposed to EE 2 from two days post-hatch had gonadal intersex at 2 ng/L (Balch et al, 2004). Fathead minnow have been completely feminized in lifecycle exposures to 4 ng/L EE 2 (Länge et al, 2001) and 3.2 ng/L (Parrott and Wood, 2002). Mummichog sex ratios appear to be affected at higher exposure concentrations (>10 ng/L EE 2 ) than other species (<5 ng/L EE 2 ).…”

“…EDSs may interfere with any part of endocrine control, including production, release, transport, metabolism, receptor binding, action or elimination. The sum total of these effects can be measured in fish laboratory bioassays designed to assess reproduction, development and growth (Patyna et al, 1999;Zillioux et al, 2001;Parrott and Wood, 2002;Seki et al, 2004). Chronic exposure to xenobiotics can induce changes to organisms not noted by shorter-term exposures (Parrott and Blunt, 2005), including factors that may be manifested at the population level, such as lower recruitment (Ankley et al, 2001).…”