Toxins in Toledo’s drinking water supply
Thousands of residents of the city of Toledo, along with parts of southeast Michigan, recently experienced a loss of water supply. The taps are back on now, but could it happen again?
The recent contamination of drinking water supplies drawn from western Lake Erie was caused by what aquatic scientists refer to as a Harmful Algal Bloom (HAB). Most algal blooms that occur in aquatic systems are green planktonic algae – true plants that are fed upon by fish and other aquatic organisms. Though sometimes a nuisance, green algae blooms are harmless to human health. But the Lake Erie HAB that shut down drinking water supplies in Toledo and parts of southeast Michigan were blue-green algae.
Blue-green algae are technically not algae. They are cyanobacteria that possess chlorophyll and photosynthesize like plants. Cyanobacteria are referred to as a harmful algal bloom (HAB) because they are capable of producing toxins that can pose health risks to people and animals. The cyanobacteria identified in the Lake Erie HAB were Microsystis, which commonly and naturally grow in the Great Lakes region. Microsystis can produce a liver toxin known as Microsystin, which at very high concentrations poses health risks.
When algae multiply so rapidly that they can be seen with the naked eye it is called an algal bloom. Conditions that lead to blooms are more likely to happen in late summer when sunlight is abundant and water temperatures are at their highest. Excess nutrients, like nitrogen and phosphorus, entering the water body provide food for both green and blue-green algae blooms. But the toxic nature of the latter results in little or no control by fish and other aquatic animals. Because of this and other factors, blue-green algae often outcompete green algae for nutrients in the water column. They multiply rapidly (bloom) in open water and in the shallow, quiet, sunny parts of inland lakes and ponds.
Unfortunately, HABs are not uncommon phenomena in Lake Erie – appearing again and again whenever sunlight, water temperatures and nutrient levels are optimum. Understandably municipal drinking water facilities, dependent on Lake Erie as a public water supply, can benefit from an early warning system. To this end the National Oceanic and Atmospheric Administration has developed a HABs bulletin for Lake Erie water supply systems.