It is well-known that perchlorate is a widespread environmental pollutant. Anthropogenic sources of perchlorate in the environment include human activities such as agriculture, industrial and military activities. Perchlorate is also considered as a thyroid-disruptor due to its main mode of toxicity; inhibition of iodine uptake by competitive inhibition of the sodium iodide symporter (NIS). In contaminated environments, chemicals very rarely occur singly. They exist as a part of a complex mixture. There is a need for more studies that expose organisms to two or more chemicals simultaneously, in order to provide better understanding of the harmful effects of these chemicals alone and together. This would enhance ecological risk assessment of chemical mixtures. This study examines the effects of perchlorate and a mixture of perchlorate and arsenic in zebrafish (Danio rerio). The study tests the hypothesis that thyroid disruption is enhanced in zebrafish exposed to a mixture of perchlorate and arsenic relative to zebrafish exposed to perchlorate alone. For this study, zebrafish were exposed to different concentrations of perchlorate alone and the mixture of perchlorate- arsenic. The effects were observed and recorded based on three major histopathological endpoints, namely, hyperplasia, follicle wall thickness and colloidal depletion. There was no significant effect on colloidal depletion and follicle wall thickness for both the perchlorate-arsenic mixture and perchlorate exposures. In contrast, there was a significant difference between control fish and fish exposed to highest concentration of perchlorate (100mg/L). A significant difference was observed in the endpoint hyperplasia for fish exposed to perchlorate-arsenic mixture at concentration as low as 10 mg/L. This study shows only one thyroid parameter (hyperplasia) altered by the perchlorate-arsenic mixture. In addition, the amount of hyperplasia seen in 100 mg/L perchlorate + 0.2 mM arsenate was greater than 100 mg/L perchlorate alone. The central hypothesis of the study is supported, indicating that a mixture of perchlorate and arsenic can induce more toxic effects in fish than just perchlorate alone (in terms of hyperplasia), thus indicating that arsenic can induce perchlorate toxicity
|Advisor:||Theodorakis, Chris W.|
|Commitee:||Jennings, David, Zhi-Qui, Lin|
|School:||Southern Illinois University at Edwardsville|
|School Location:||United States -- Illinois|
|Source:||MAI 53/06M(E), Masters Abstracts International|
|Keywords:||Exposure, Histhopathological endpoints, Hyperplasia, Perchlorate, Perchlorate-arsenic, Thyroid gland in zebrafish|
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