Foul Play in The Great Lakes

The past few summers have left a bad taste in the mouths of residents living on the shores of the Great Lakes and St. Lawrence River, where foul smelling, bad-tasting water has increased apprehensions about the safety of local drinking-water supplies. Scientists at Environment Canada's National Water Research Institute (NWRI) have partnered with the Ontario Clean Water Agency (OCWA) to discover what is causing the problem and what they can do to prevent it.

In 1999, the situation lasted a record four weeks. The main source of the taste and odour problems in the water is the naturally occurring compounds geosmin and 2-methylisoborneol (MIB), which can be detected by humans at very low levels. Geosmin and MIB are produced by the bacteria Actinomycetes and some species of blue-green algae, though the exact organisms are not known. Geosmin is thought to originate in the water column and produces an earthy odour, while MIB is produced in the sediment or benthic layer and gives off a musty odour. These compounds resist oxidation and are difficult to remove by standard treatment in water filtration plants.

Over a period of six weeks, NWRI researchers sampled Lake Ontario water near the intakes of two water treatment plants in the Region of Peel at depths varying from 2 to 70 metres from the surface and distances ranging from 0.02 to 10 kilometres from shore. When the samples were analyzed, scientists did not detect MIB, but found concentrations of geosmin ranged from 0.9 to 223 nanograms per litre—higher than any previously recorded. It had been thought that geosmin might originate from decomposing benthic algae near shore; however, samples from the shallowest nearshore site were similar to those from other sites, so there was no support for this theory.

Researchers have come up with several potential solutions as a result of their findings. Over the summer, Lake Ontario stratifies into three thermal zones: a warm upper layer, a transition zone, and a cold bottom layer. They discovered that water extracted from the deepest part of the cold bottom layer contained less geosmin than surface water, leading them to believe it could be possible to avoid the geosmin-tainted water by extending water intake pipes into this layer.

Another option, which is already in use in some areas, is to place granular activated-carbon filters on top of conventional filters in water purification plants. Studies have shown these filters remove an average of 80 per cent of geosmin and 60 per cent of MIB.

In 2000, several regional municipalities, including Peel, Hamilton-Wentworth, Durham, Niagara, York, Toronto and Halton, have joined the taste and odour research consortium and are funding NWRI and the Ontario Ministry of the Environment to continue studying the problem. Scientists will now try to determine exactly which organisms cause the geosmin and 2-methylisoborneol and see if they can be predicted or controlled. They will also expand their research to find out if other factors such as nutrient distribution, algal population levels, and zebra mussels are contributing to the recurring taste and odour problems.

The taste and odour episodes vary from one year to another, therefore the problems cannot be solved rapidly. It is expected that the studies will proceed for several years to account for differences in the weather affecting the biota of the lake. The results of this research will be of value to Ontario municipalities trying to address taste and odour problems.

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