Sunday, October 10, 2010

Is Pasir Ris water really unsafe?

As a follow-up to the news update on the fecal bacteria laden water of Pasir Ris, this news may throw more questions (instead of light) on the issue of poor water quality at Pasir Ris.

First, a quick summary. A press release from NEA (Sep 2010) stated that the water at Pasir Ris Beach is unsafe due to the off-specs level of Enterococcus (a bacteria) in the water. Enterococcus is supposed to indicate the level of fecal contamination. More Enterococcus of course means more fecal contamination, implying a higher possibility of the presence of human pathogens.

Why don't we analyse the water directly for the pathogens? There are simply too many pathogens to test for so going down this route will easily lead to a logistical nightmare. Therefore, we stick to an indicator organism, something that is strongly linked to humans. Since Enterococcus (supposedly) comes from the human gut, its presence is (supposedly) sufficient to prove the contamination of the water by humans.

Going back a bit backwards in the history of water quality testing, the title of indicator organism for fecal contamination used by held by a group of bacteria known as coliforms. Not surprisingly, coliforms are also found in the human gut and its presence used to conclude the presence of human contamination. Unfortunately, coliforms are also found in other animals and soil. Some years back, Enterococcus has taken over this position as it was found to produce a better correlation to many human pathogens found in sewage. (Opps, the summary seems a bit longer than I initially thought.)

Ok, enough of summarising. Check these out:
1. Evaluation of Chemical, Molecular, and Traditional Markers of Fecal Contamination in an Effluent Dominated Urban Stream

2. How To Define "Safe" Water? Water Pollution: Southern California study highlights the limits of bacteria used as fecal indicators

The study basically argues that even Enterococcus is not a good enough indicator for fecal contamination in water. Why? Because it can also be found naturally in the river bed (in the study). In fact, it can actually grow in the river bed under favourable conditions i.e. good nutrient availability. Therefore, a bacterial count using Enterococcus tends to be overestimated with regards to the actual fecal contamination. (Granted, the study took place in fresh water and not seawater. But being such a versatile creature, Enterococcus can tolerate a wide range of conditions - pH, temperature, salinity, presence/absence of oxygen so it will not be surprising to find it thriving nicely in seawater.)

Is the water at Pasir Ris safe then? Your guess is as good as mine.

However, the study did recommend a substitutre for Enterococcus - something known as human-specific HF183 Bacteroides. This bacteria is supposedly (?) found only in the human gut. Testing for the presence of its genetic material will provide an accurate (?) picture of the amount of fecal contamination in water.

Will it really work?

Me? I will wait for the next piece of study to throw a spanner into this theory :-)

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