Microbial risk assessment for recreational use of the Kallang Basin, Singapore

Abstract

The water quality in the Kallang Basin, Singapore, was analyzed in order to determine how safe the waters are for recreational users, specifically focusing on dragon-boat racers. The Public Utilities Board of Singapore has been managing reservoirs under the "Active, Beautiful, and Clean Waters Programme" in order to help the public recognize the value of their scarce water sources. Therefore, microbial risk assessments were conducted on locations along the Kallang Basin to analyze any diurnal or spatial differences in probabilities of illness, and establish guideline geometric mean concentrations. Samples were collected at four different locations along the Kallang Basin every four hours during a 48-hour period. Samples were then analyzed for Enterococci and E. coli using most-probable-number methods. Adenovirus was analyzed by Liu (2014) using quantitative polymerase chain reaction. Based on the Wiedenmann et al. (2006) statistics-based risk model, no-observed-adverse-risk levels or guideline geometric-mean levels were established at 128 colony forming units (CFU) / 100 mL for Enterococci and 697 CFU/ 100 mL for E. coli. Based on these guideline geometric-mean concentrations, all of the stations exceeded the tolerable illness level for indicator bacteria at certain times, with peak concentrations at 7:00 A.M. and 11:00 A.M. However, for adenovirus, the probabilities of illness did not exceed the tolerable level based on appropriate dragon-boat racer ingestion rates. Statistical analysis showed that a high correlation existed between adenovirus concentrations and E. coli concentrations. Future studies should analyze specific locations along the Kallang Basin that contribute to high concentrations of indicator bacteria and viruses.