geosmin or geospin? a clearer picture of cape town's 'earthy' water

Submitted by turbosprout on Fri, 2012-02-17 07:49

Cyanobacteria: Anabaena solitaria ~ the organism associated with geosmin in TheewaterskloofCyanobacteria: Anabaena solitaria ~ the organism associated with geosmin in TheewaterskloofAre you smelling it too? For a couple of weeks now I've been aware that our water tastes a bit funny and there's an odour too. It's a sandy, earthy kind of smell, but not earthy as in the wonderful smell of worm castings or compost - that fertile, rich smell. No, this is a dusty, decaying or stale earthiness. It's subtley unpleasant. I thought that it was perhaps time to change the water filter we use on our incoming supply.

Then all was made clear by an email received from the City of Cape Town, explaining that what we're smelling / tasting is Geosmin or MIB (2-Methyl-iso-Borneol), two "naturally occuring compounds found in surface waters (rivers and dams) as organic molecules produced by blue-green algae."

"Absolutely safe"
The city assures us that the water is "absolutely safe to drink".

“The water, however, is perfectly

safe and fit for human consumption. Continuous water quality monitoring by our South African National Accreditation System (SANAS) accredited laboratory has revealed elevated Geosmin concentrations, greater than 10 nanograms per litre (ng/l). In general, the human perception threshold is about 15 and 20 ng/l for Geosmin odour and taste respectively and people with a heightened sense of smell and taste would be the first to notice the presence of Geosmin in their water supply. These are extremely low concentrations and it should be noted that a nanogram is a billionth of a gram,” said the Manager of the City’s Bulk Water Branch, Peter Flower.

The email continues with a series of Frequently Asked Questions that are designed to put our minds at ease about our water supply. Check it out here.

Despite the authorities reassurances, being curious in nature, I'm always inclined to do some of my own research. I wondered, after all, that if my body has evolved the sensitivity to detect the equivalent of one teaspoonful of geosmin diluted in "200 Olympic-sized swimming pools" (an olafactory feat of impressive proportions), there might be some good reason for it.

Another view
I stumbled on the "offical weblog" of DH Environmental Consulting, and they seem to have a particular competancy when it comes to assessing and managing aquatic ecosystem and water-related environmental problems. Their website states that they have recently completed their 600th contract, and it is chock full of information and pictures of the interesting organisms living in our water. They also seem to have an obsession with algal flora (I guess it's their business) and know a thing or two about cyanobacteria (blue-green algae).

So when experts like these caution the City to be "fully-aware of what the allied issues and risks might be" before giving the green light, I sit up and take notice.

DH Environmental's concern is that although Geosmin is not of itself a health hazard, it's presence in water supplies points to the possible presence of a "toxin that all ... cyanobacteria produce, namely the neurotoxin BMAA (betamethylaminoalanine)".

They go on to state that BMAA and its possible role in neurodegenerative disorders such as ALS, Parkinson's and Alzheimers, is currently the focus of research at several universities and institutes around the world.

So do we believe the City that our water supply is "absolutely safe", or should the Geosmin problem be taken more seriously? I'd like to know, for example, what controls are in place by the City to remove toxins from natural sources like cyanobacteria from the water supply and whether water quality consultants like DH Environmental feel these measures are adequate.

I'm not about to run out and buy bottled water (never a good idea), but I'll be replacing our water filter and making a few trips to the Newlands spring again.

Picture credit: DH Environmental Consulting

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