Yogyakarta- Uncontrollable traditional gold mining in Sangon River, Kulon Progo regency, has caused river sediment pollution by mercury. Some mercury content in the sediment has transformed due to the activities of indigenous bacteria. The transform has produced species of mercury that is more toxic, such as methyl mercury that generally accumulates in the sediment.
That was delivered by lecturer of Faculty of Math and Natural Sciences, Sriwijaya University, South Sumatera, Drs. Suheryanto, M.Si, in his open exam of doctoral program at UGM Graduate School on Monday (20/12).
In his dissertation entitled Demethylation of Methyl Mercury by Bacteria Isolated from Sediment of Sangon River, Suheryanto explained that the research aims to study methyl mercury in sediment of Sangon River and its transformation by indigenous bacteria.
“The research is to determine total pollution level of mercury and methyl mercury in the river’s sediment, and to get indigenous bacteria that is resistant to metal mercury and has active role in demethylation of methyl mercury, then to study the mechanism of methylmercury demethylation by isolating indigenous bacteria,” said Suheryanto who passed with honours.
In front of board of examiners led by Prof. Dr. Hartono, DEA., DESS, Suheryanto explained the research about methylmercury in Sangon River that started with mercury analysis in the sediment of the river adopted GLS (gas liquid chromatography) method and CV-AAS (cold vapour atomic absoption spectrometry). The result showed the total pollution level of mercury and methyl-mercury varied. Total mercury in upstream is 236, 67 ng/g, midstream is 154,25 ng/g, downstream 70,25 ng/g, whereas methyl mercury in upstream is 48,50 ng/g, midstream 96,25 ng/g and downstream is 55,00 ng/g.
“The presence of methyl mercury in the sediment proves that mercury was oxidized to mercury ion, then experienced methylation by sediment indigenous bacteria,” he said. He added that methyl mercury is toxic to water biota including bacteria, even deathful for sediment indigenous bacteria. “The result is several tolerant bacteria emerging and some of them can use methylmercury as energy source,” he said.
Meanwhile, in isolating bacteria with culture technique that is enriched with one harvesting system, there are 82 isolate bacteria, methylmercury users, that can be isolated. After being selected, only six isolated bacteria are resistant and grow using methyl mercury. The isolate are SDM 41, SDm 78, SDm 81, SDPM 8a, SDPM 8b, and SDPM 24.”The six isolate bacteria can grow in the medium consisting methyl mercury in several concentrations,” he said.
The six isolates have been identified with BD phonix tool and have specific character in methyl mercury demetilation. The six isolate bacteria have similarity with brevundimonas diminuta (strain SDM 41), Bacillus cereus (strain SDm 78), Empedobacter brevis (strain SDM 81), klebsiella pneumonia (strain SDPM 8a), pseudomonas aeruginosa (strain SDPM 8b) and spingomonas paucimobilis (strain SDPM 24).
Besides, Suheryanto also conducted ability test of methyl mercury demethylation through test of growing to identify methyl mercury demethylation mechanism by bacteria in laboratory scale. It was known that methyl mercury demethylation ability shows the concentration reduction of methyl mercury in final exponential phase of growth. However, the highest reduction was shown by strain SDM 81 and SDM 8a.