| Popis: |
This thesis presents the development of three new bioassays for the detection of compounds disrupting the early development of echinoid larvae from hatching to metamorphosis, and the interference with cellular efflux pumps. These assays come in addition to the already existing sea urchin fertilization assay and the short term ELS assay (48 or 96 hours. This chapter summarizes the contents of the thesis. In Chapter 1, background information and objectives of the thesis are presented. Firstly the risks that POPs pose to the marine environment are introduced, as well as the need to develop tools to assess toxic effects of exposure during the most sensitive period of the life cycle of organisms, their early life development. Secondly, echinoids are presented as an invertebrate marine animal model to develop early life development bioassays. Lastly, the aim of the thesis and the experimental approach chosen is outlined. Chapter 2 describes the development ofa new 16-day echinoid prolonged early life stage (p-ELS) bioassay that includes prolonged observation for the detection of possible delayed adverse effects during embryogenesis and larval development of the sea urchin Psammechinus miliaris. Subsequently, the newly developed bioassay was applied to study the effects of key marine POPs. Mortality, morphological abnormalities and larval development stages were quantified at specific time points during the 16-day experimental period. In contrast to amphibians and fish, P. miliaris early life development was not sensitive to dioxin-like toxicity in the p-ELS test. Triclosan (TCS) levels higher than 500 nM were acutely toxic during embryo development. Morphological abnormalities were induced at concentrations higher than 50 nM hexabromocyclododecane (HBCD) and 1000 nM tetrabromobisphenol A (TBBPA). Larval development was delayed above 25 nM HBCD and 500 nM TBBPA. Heptadecafluorooctane sulfonic acid (PFOS) exposure slightly accelerated larval development at 9 days post fertilization (dpf). However, the accelerated development was no longer observed at the end of the test period (16 dpf). The newly developed 16-day echinoid p-ELS bioassay proved to be sensitive to toxic effects of POPs and effects can be monitored for individual echinoid larvae. The most sensitive and dose related endpoint was the number of developmental penalty points. By manipulation of the housing conditions, the reproductive season could be extended from 3 to 9 months per year and the p-ELS experiments could be performed in artificial sea water as well. In Chapter 3 a metamorphosis assaywas developed, using the sea urchin P. miliaris, to detect and quantify the potency of persistent organic pollutants (POPs) to disrupt thyroid hormone (TH) induced metamorphosis. Similar to vertebrates, echinoids have a TH induced metamorphosis, making them a potential model organisms to study TH disruption. Larvae were exposed to test compounds from the 8-armed pluteus stage until metamorphosis completion. Thyroxine (T4) accelerated metamorphosis (EC50 0.12 and 0.09 nM experiment A and B, respectively), whereas the TH synthesis inhibitor thiourea (TU) (IC50 0.1 and 0.04 mM experiment A and B, respectively) or the iodine uptake inhibitor potassium thiocyanate (KSCN) delayed metamorphosis (IC50 |
