Comparing vitellogenin induction by 17β-estradiol in male Danio rerio through both a tritrophic bioaccumulation model and a bioconcentration model

Background/Question/Methods

The steroid hormone 17β-estradiol (E2) is naturally produced by humans. It is excreted into the water and not completely filtered out by sewage treatment plants. Its presence in the aquatic ecosystem is causing physiological disruptions in many aquatic organisms. Being lipophilic allows 17β-estradiol to be stored in primary producers, giving E2 the ability to possibly bioaccumulate, and therefore transfer up the food web. The chemical E2 can also bioconcentrate in aquatic species, specifically fish, which implies it can be accumulated through non-dietary routes. A tritrophic model using diatoms (Navicula radiosa), daphnia (Daphnia pulex), and zebrafish (Danio rerio) served to evaluate the bioaccumulation and potential trophic transfer by exposing diatoms to E2. A second bioconcentration model determined the ability of E2 to concentrate in D. rerio via direct exposure of water treated with E2. In both experiments the same exposure conditions were used; High concentration of E2 (800 ng/mL), Low concentration of E2 (40 ng/mL), and Control (0 ng/mL). There were ten male D. rerio in each group and six were randomly chosen for a whole body homogenate sample to quantify the amount of vitellogenin (Vtg), an egg yolk precursor protein, production using an ELISA.

Results/Conclusions

Initial ANOVA results show there were no significant differences between the densities of the N. radiosa over the ten day exposure period, demonstrating that E2 had no significant effect on N. radiosa. After feeding the N. radiosa to D. pulex, the survival rate of D. pulex remained the same between treatments demonstrating that E2 had no significant effect on D. pulex. An effect was observed, however, in the health of D. rerio.  Fifty prevent of fish in the high E2 treatment showed symptoms of swollen, red eyes and localized hematoma in the abdominal area.  With completion of our data analysis we expect to be able to quantify, via Vtg production, the extent to which E2 can pass through two trophic levels and/or bioconcentrate in D. rerio. Our results will begin to explain the potential for bioaccumulation and/or bioconcentration of E2 in an aquatic community, which can lead to predictions about the potential for E2 bioaccumulation in humans.