Development of an Tier II two-generation test guideline for the sheepshead minnow
Development of a guideline for a fish Tier II Test that can be used to determine whether a chemical or chemical mixture adversely affects the organism through endocrine-mediated pathways, and to evaluate those effects with respect to the estrogen, androgen, and thyroid systems. The test includes exposure of multiple generations of the estuarine fish, sheepshead minnow, throughout all life stages.
The objectives of this research are to: 1) Incorporate refinements to current sheepshead minnow early life-stage and chronic exposure guidelines, and demonstrate a transferable two-generation toxicity test guideline; 2) Assess the value added impact of a two-generation test over refined early life-stage and chronic exposure guidelines; and 3) Examine the utility of application of statistical models which may predict population-level effects of reproductive toxicants. The demonstration exposures are being conducted with two pharmaceuticals, a model estrogen, 17â-estradiol and a model androgen, 17â-trenbolone. Testing approaches and endpoints identified as having the greatest potential to singularly or collectively indicate reproductive impairment are being incorporated in the two-generation test guideline.The following endpoints have evaluated from a completed test with estradiol: survival, reproductive behavior, spawning frequency and egg production, fertility, time to hatch, and hatching success, larval morphology, secondary sex characteristics, body length and weight, histology (gonad, liver, kidney and thyroid), and plasma/tissue levels of vitellogenin and plasma sex steroid levels. The results from the two-generation test will be compared to segments of the exposure that represent established shorter-term 28 day and single life cycle exposures to determine what additional benefits are gained and at what additional cost. To make full use of these data, we are incorporating population modeling in the data analyses. A matrix model will utilize different endpoints at different stages of development with weighted sensitivity to fully identify the contribution of each of the endpoints. To explore contributions of other life history events such as predation and catastrophic events, stochastic simulation models will also be applied to the data collected.
A transferable guidance document for conducting a two-generation exposure of the estuarine sheepshead minnow will be produced. This guidance is provided to OPPTS/OSCP for Tier II testing of chemicals for endocrine disrupting activity. A "value-added" assessment will be conducted to evaluate the predictive capacity of various segments of the exposure to identify outcomes from the entire two-generation exposure.
Geraldine Cripe at email@example.com