Thesis (M.Sc.)--Chulalongkorn University, 2011

17α-methyltestosterone (MT) is a male hormone used commonly to produce an all male population in Nile tilapia farming. MT may remain in the masculinization process and be released into the surrounding water and soil bodies causing adverse impact to ecosystems. This study aims to investigate the occurrence of MT in masculinization pond of Nile tilapia fry and its discharged area. MT was extracted from water and sediment samples using SPE and LPE by methanol, respectively. MT concentration was determined using UPLC-MS/MS. The average percent recoveries of the extraction method when MT was spiked into water samples (10 and 100 ng/L) were 80 - 84 %. For the sediment samples, the average percent recoveries (1 and 10 µg/kg) were 60 – 71 %. The monitoring during 1-day period was performed to define the time of the day that MT reached the maximum concentration. The maximum MT concentrations in most compartments (water, suspended solid, and settled solid phases) occurred at the end of the last feeding time (16.00). MT was input into the pond through the feed and was released into the environments by two approaches: 1) with the daily overflow water (water phase and suspended solids phase) and 2) with the water (water phase and suspended solid phase) and settled solid that remained in the pond on the last day of operation (day 30). In the overflow water, the overall concentrations of MT (water phase and suspended solid phase) were 0.3 – 39.5 ng/L. For MT remaining in the pond on day 30, the overall MT concentration was calculated by assuming that MT in all compartments (water, suspended solid, and settled solid phases) distributed homogeneously in the pond as at the end MT in all compartments were released with the pond water. The level of MT was found to be 0.595 ng/L. Although the ranges of the MT concentrations found in the overflow water were in the ranges reported to affect organisms (6.5 ng/L), these levels of MT can be reduced due to effect of dilution when the overflow water was released into natural receiving water. Comparing to the total mass of MT supplied into the pond with the feed (148.85 mg), 0.33 % (492.85 µg) of MT was released with the overflow water along 30 days of operation. MT remaining in the pond on day 30 can be accounted as 0.0009 % (1.33 µg) of the total MT supplied to the pond. In overall, 0.333% (494.18 µg) of MT supplied to the pond was released into the environment. In the overflow water, the total mass of MT was 492.85 µg which can be accounted for 99.73 % of overall of MT released into the environment. Comparing to the overall MT released, MT in the water phase was 96.89 % and was 2.84 % in the suspended solid phase. MT remaining in the pond was 0.27 % of the overall MT released. Combining all MT released, MT distributed 97.06 %, 2.93 %, and <0.005 % in water phase, suspended solid phase, and settled solid phases, respectively. The priority should be given to the overflow water to reduce the risk of MT released into the environment. To investigate the occurrence of MT in the discharged area, the highest concentrations of MT were found at the inlet of the concrete ditch (0.29 ng/L for water and 0.1 µg/kg for settled solids) and the concentrations reduced to 0.21-0.22 ng/L and 0.06-0.07 µg/kg for water phase plus suspended solid phase and settled solid, respectively, at the outlet point of the concrete ditch. The MT concentrations in the receiving water were in the range of 0.13-0.14 ng/L and it was 0.01 µg/kg in the receiving sediment. The levels of MT in the receiving water were found to be lower than the levels reported to affect organisms (6.5 ng/L). The further study should be done to clarify fate of MT and to develop the method to detect androgenic activity under low levels in the masculinization process of Nile tilapia fry.