Thesis (M.Sc.)--Chulalongkorn University, 2009

It is a common practice in the aquaculture of Nile tilapia to use 17α-methyltestosterone (MT) impregnated in fish feed to obtain an all male population. However, only little is known about the occurrence and fate of MT in the environment. Therefore, one objective of this study was to qualitatively and quantitatively determine MT in sediment samples obtained from a Nile tilapia earthen nursery pond as MT has been shown to preferably sorb onto sediment. In addition as the second objective of this study, a method for the extraction and purification of MT from sediment samples had to be developed, as there is no comprehensive protocol reported in literature. The developed method was based on liquid-phase extraction in combination with sonication. Optimized parameter of the extraction procedure included extraction solvent, extraction time, and sonication time. A recovery rate of 97.01% ± 3.36% RSD (n= 5) could be achieved and additional residues of MT in sediment could be extracted with sonication. Moreover, sediment samples were taken during hormone treatment period to monitor concentration of MT during its application. The obtained results indicated that MT could be found in all sediment samples; although, the concentrations of MT measured were in the low µg/kg-range. This is the first study reporting the occurrence of MT in samples taken from the environment.