Geosmin contamination status of raw and treated waters in Sri Lanka

Off taste and odour in drinking water cause a serious issue in some parts of Sri Lanka and higher number of customer complaints is related to off taste and odour in treated water. Water sources are having diverse range of algae and cyanobacteria community and most of them produce chemical compounds like geosmin. A simple and sensitive modified method for the determination of earthy odorant geosmin in water was developed by headspace solid-phase micro extraction coupled with gas chromatography-mass spectrometry. Quantification of the geosmin contamination level in 22 drinking water sources (raw water bodies and water treatment plants) was carried out for the first time in Sri Lanka. Results revealed that 68% of the sampling locations exceed the human threshold level of geosmin (5 ng L^-1). The concentration of geosmin in raw water bodies ranged from 7.825 to 10.929 ng L^-1 whereas in treated water it ranged from 8.113 to 11.196 ng L^-1.？ Geosmin concentrations in treated water were higher than in the respective raw water. Some taste and odour producing cyanobacteria and algae were identified and quantified in the same water bodies where geosmin was detected. Anabaena sp., Cylindrospermopsis sp., Microcystis sp., Oscillatoria sp. and Volvox sp. are the common cyanobacteria and algae in water bodies. Total taste and odour forming cyanobacteria and algae count have shown a significantly positive correlation with geosmin concentration (p < 0.05). A significant positive correlation was found between geosmin and total phosphorus (p < 0.05), electrical conductivity (p < 0.05) and pH (p < 0.05), factors that normally favour cyanobacterial growth.

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