JWARP  Vol.12 No.6 , June 2020
Risk Management of Cyanotoxins in Singapore
Abstract: Cyanotoxins produced by cyanobacteria pose significant challenges to water resource management due to the potential impacts they have on human health. Cylindrospermopsin (CYN) and microcystins (MC) are the more commonly detected cyanotoxins in Singapore’s reservoirs. Among the MC congeners monitored locally, the most frequently detected variants are MC-RR (37.6%), followed by MC-LR (25.6%). MC-LA and MC-YR are the least frequently detected variants (7.1%). No cyanotoxins have been detected in Singapore’s treated drinking water. Singapore’s National Water Agency (PUB) and the National Environment Agency (NEA) developed recreational water quality guidelines using Chl a concentrations of 50 μg/L. In local surface waters, long-term data showed that at 50 μg/L of Chl a, MC-LR concentrations ranged from <0.025 μg/L to 1 μg/L. In addition to using Chl a concentrations, Microcystis cell counts in reservoir water have also been used to manage cyanotoxin risk in drinking water. Specifically, routinely monitored data from all 17 Singapore reservoirs indicated that to keep MC-LR concentrations below the WHO provisional guideline of 1 μg/L in drinking water, Microcystis cell counts needed to be <10,000 cells/ml. Culture experiments using local Microcystis isolates showed M. aeruginosa produced the most MC compared to M. ichthyoblabe, M. flos-aquae, and M. viridis. Based on the maximum toxin cell quota equivalent to the WHO provisional guideline for MC-LR of 1 μg/L in drinking water, a 5000 cells/ml cell count guideline was derived for M. aeruginosa. This cell count has also been incorporated into Singapore’s cyanotoxin risk management framework for reservoirs.
Cite this paper: Lim, M. , Tay, H. , Devotta, D. , Mowe, M. and Mitrovic, S. (2020) Risk Management of Cyanotoxins in Singapore. Journal of Water Resource and Protection, 12, 512-525. doi: 10.4236/jwarp.2020.126031.

[1]   Loftin, K.A., Graham, J.L., Hillborn, E.D., Lehmann, S.C., Meyer, M.T., Dietze, J.E. and Griffith, C.B. (2016) Cyanotoxins in Inland Lakes of the United States: Occurrence and Potential Recreational Health Risks in the EPA National Lakes Assessment 2007. Harmful Algae, 56, 77-90.

[2]   Paerl, H.W. and Scott, J.T. (2010) Throwing Fuel on the Fire: Synergistic Effects of Excessive Nitrogen Inputs and Global Warming on Harmful Algal Blooms. Environmental Science & Technology, 44, 7756-7758.

[3]   Manning, S.R. and Nobles, D.R. (2017) Impact of Global Warming on Water Toxicity: Cyanotoxins. Current Opinion in Food Science, 18, 14-20.

[4]   Koreiviene, J., Anne, O., Kasperoviciene, J. and Burskyte, V. (2014) Cyanotoxin Management and Human Health Risk Mitigation in Recreational Waters. Environmental Monitoring and Assessments, 186, 4443-4459.

[5]   Yen, H., Lin, T. and Liao, P. (2011) Simultaneous Detection of Nine Cyanotoxins in drinking Water Using Dual Solid-Phase Extraction and Liquid Chromatography—Mass Spectrometry. Toxicon, 58, 209-218.

[6]   Yoo, R., Carmichael, W., Hoehn, R. and Hrudey, S. (1995) Cyanobacterial (Blue- Green Algal) Toxins: A Resource Guide. AWWA Research Foundation and American Water Works Association, Denver.

[7]   Dittmann, E., Fewer, D.P. and Neilan, B.A. (2012) Cyanobacterial Toxins: Biosynthetic Routes and Evolutionary Roots. FEMS Microbiology Reviews, 37, 23-43.

[8]   Shang, L., Feng, M., Liu, F., Xu, X., Ke, F., Chen, X. and Li, W. (2015) The Establishment of Preliminary Safety Threshold Values for Cyanobacteria Based on Periodic Variations in Different Microcystin Congeners in Lake Chaohu, China. Environmental Science Processes & Impacts, 17, 728-739.

[9]   World Health Organization (2017) Guidelines for Drinking Water Quality. 4th Edition, Gutenberg.

[10]   U.S. EPA (United States Environmental Protection Agency) (2015) Drinking Water Health Advisories for Two Cyanobacterial Toxins. EPA-820F15003.

[11]   Chorus, I. (2012) Current Approaches to Cyanotoxin Risk Assessment, Risk Management and Regulations in Different Countries. Federal Environment Agency (Umweltbundesamt).

[12]   Ibelings, B.W., Backer, L.C., Kardinaal, W.E. and Chorus, I. (2015) Current Approaches to Cyanotoxin Risk Assessment and Risk Management around the Globe. Harmful Algae, 49, 63-74.

[13]   Mowe, M.A.D, Mitrovic, S.M., Lim, R.P., Furey, A. and Yeo, D.C.J. (2015) Tropical Cyanobacterial Blooms: A Review of Prevalence, Problem Taxa, Toxins and Influencing Environmental Factors. Journal of Limnology, 74, 205-224.

[14]   Cunha, D.G.F., Dodds, W.K. and Loiselle, S.A. (2018) Factors Related to Water Quality and Thresholds for Microcystin Concentrations in Subtropical Brazilian Reservoirs. Inland Waters, 8, 368-380.

[15]   Mitrovic, S.M., Hardwick, L. and Dorani, F. (2011) Use of Flow Management to Mitigate Cyanobacterial Blooms in the Lower Darling River, Australia. Journal of Plankton Research, 33, 229-241.

[16]   Huszar, V.L.M., Silva, L.H.S., Marinho, M., Domingos, P., Sant’Anna. C.L. (2000) Cyanoprokaryote Assemblages in Eight Productive Tropical Brazilian Waters. Hydrobiologia, 424, 67-77.

[17]   Prakash, S., Lawton, L.A. and Edwards, C. (2009) Stability of Toxigenic Microcystis Blooms. Harmful Algae, 8, 377-384.

[18]   World Bank (2018) The World Bank Data: Population Density (People per sq. km of Land Area)—Singapore.

[19]   Meteorological Service Singapore (2020).

[20]   Mowe, M.A.D. (2015) Toxic Cyanobacteria in the Tropics: Effects of Environmental Factors on the Growth and Toxin Production of Microcystis species Isolated from Singapore reservoirs. Unpublished Ph.D. Thesis, National University of Singapore, Singapore.

[21]   Mowe, M.A.D, Porojan, C., Abba, F., Mitrovic, S.M., Lim, R.P., Furey, A. and Yeo, D.C.J. (2015) Rising Temperatures May Increase Growth Rates and Microcystin Production in Tropical Microcystis Species. Harmful Algae, 50, 88-98.

[22]   World Health Organization (2003) Algae and Cyanobacteria in Fresh Water. Guidelines for Safe Recreational Waters, Volume 1—Coastal and Fresh Waters. WHO Publishing, Geneva, 136-158.

[23]   NHMRC, NRMMC (2011) Australian Drinking Water Guidelines Paper 6 National Water Quality Management Strategy. National Health and Medical Research Council, National Resource Management Ministerial Council, Commonwealth of Australia, Canberra.

[24]   PUB Singapore’s National Water Agency (2020).

[25]   Baird, R.B., Eaton, A.D. and Rice, E.W., Eds. (2017) Standard Methods for the Examination of Water and Wastewater. 23rd Edition, American Public Health Association, American Water Works Association, Water Environment Federation, Washington D.C.

[26]   Bolch, C.J.S. and Blackburn, S.I. (1996) Isolation and Purification of Australian Isolates of the Toxic Cyanobacterium Microcystis Aeruginosa Kütz. Journal of Applied Phycology, 8, 5-13.