Testing for endocrine disruptors in South African waters : a comparative study employing in vitro and in vivo screening approaches

[摘要] ENGLISH ABSTRACT: Numerous natural and synthetic chemicals are known to interfere with the endocrine systems of wildlife and humans, i.e., endocrine disruptive chemicals (EDCs). Surface water bodies represent a major sink of EDCs and aquatic vertebrates including fish and amphibians are, therefore, at risk. Although research in the field of endocrine disruption has proliferated globally in the past two decades, only limited work describing the status of surface water has been performed in the South African context.The aims of this dissertation are: (1) to provide a detailed overview of the present literature on endocrine disruptive potential, i.e., EDC associated biological activity in South African surface waters; (2) address certain literature gaps by screening surface water, collected from different South African water bodies, using in vitro reporter gene assays (RGAs) and gene expression based biomarkers in Mozambique tilapia, Oreochromis mossambicus, exposed in vivo; (3) to compare the results of the in vitro hormone receptor RGAs and the in vivo gene expression based biomarkers to assess whether the risks predicted correspond; (4) evaluate the potential of O. mossambicus as environmental sentinel and source of biomarkers for potential disruption of the reproductive, thyroid and interrenal endocrine systems.The majority of research on endocrine disruption in South African surface waters has been focused on reproductive targets, whereas potential disruption of the thyroid, adrenal, pancreatic and other metabolism linked endocrine pathways are less well described. An inter-seasonal assessment of the Upper Olifants River (Mpumalanga) indicated alarmingly high concentrations of steroid estrogens and potent estrogenic activity in vitro in water collected from the close proximity of a waste water treatment plant (WWTP), indicating local fish may be adversely affected. Future studies evaluating the reproductive systems of wild captured fish inhabiting the Upper Olifants River will be of value. No association could be shown between altered endocrine signalling and the incidence of obesity and pansteatitis in the O. mossambicus population inhabiting Loskop Dam (Mpumalanga). Evidence of disrupted thyroid signalling was, however, observed in Loskop Dam fish relative to an alternative population. Gene expression biomarkers representing the reproductive, thyroid and interrenal systems in juvenile O. mossambicus suggest limited effects associated with exposure to surface water contaminated with neutralized acid mine drainage, containing high concentrations of Al, Mn, Ni, Co and Cu. In addition, evidence is given indicating the potential risk of crude oil contamination in fresh water to the reproductive and thyroid systems as well as lipid metabolism in wildlife. No significant changes in the expression of a selection of endocrine linked genes was, however, observed in Xenopus laevis tadpoles exposed for a short period to surface water collected from a freshwater pan into which crude oil contaminated water is periodically discharged. Further investigation, and in particular longer term exposures, as well as the evaluation of aquatic fauna collected from (environmental) fresh water bodies contaminated with crude oil are required. Surface water collected from river mouths and harbours in the eThekwini Metropolitan and City of Cape Town was shown to exhibit estrogenic and anti-androgenic activity in vitro, suggesting the reproduction of fish populations may be impaired. Future studies evaluating the endocrine systems of wild-captured fish from the aforementioned coastal systems are needed.The risks associated with exposure to surface water predicted by in vitro RGAs did not in all cases correspond to the potential biological activity indicated by in vivo gene expression based biomarkers. This study, therefore, provides evidence supporting the use of a combination of in vitro and in vivo techniques to evaluate surface water for endocrine disruptive activity/risk. Juvenile O. mossambicus exposed for a short period was not sensitive to estrogenic substances, but biomarkers relating to thyroid disruption are more promising.

[发布机构] Stellenbosch University