What Happened to Toledo’s Drinking Water: Understanding Microcystins

This summer, 500,000 residents in and around Toledo, Ohio were alerted that their tap water had been declared undrinkable as a result of microcystin contamination.  For several days, residents could not shower or cook with their tap water and they were instructed to drink bottled water while some restaurants, schools and businesses closed, inconveniencing many.  What is microcystin and how did it get into Toledo’s tap water?

What are Microcystins?

Microcystins are a large class of naturally occurring toxic chemical substances produced by waterborne bacteria known as Microcystis, also called “blue-green algae” or “cyanobacteria.”  Nutrient-rich wastewater and agricultural runoff into water bodies fuel the growth of Microcystis blooms such as one in Lake Erie, the Toledo area’s water source.  According to the Environmental Protection Agency, these blooms “can persist with adequate levels of phosphorous and nitrogen, temperatures in the 5 to 30 degree C (41 to 86 degrees F) range and pH in the 6 to 9 range, with most blooms occurring in late summer and early fall.” Microcystin  (the toxin)  is released when the bacteria die and their cells break open.

Microcystins can be toxic to the human liver and can cause diarrhea, respiratory symptoms and skin rashes.  They are stable at high temperature, so boiling tap water was not an antidote to the problem; in fact, boiling has the potential for making the problem worse by evaporating water and therefore making the microcystin concentration greater.  The degree of toxicity of microcystin depends upon which varieties are present in water. A recent report in Chemical and Engineering News noted the Toledo incident consisted of 60-80 percent microcystin-LR, the most common variety and also considered the most toxic.

Water Treatment of Microcystin

The Collins Park Water Treatment Plant used an enhanced treatment plan to remove microcystins in Toledo water, according to the Chemical and Engineering News report.  First, extra powdered activated carbon helped bind or “adsorb” microcystin to the surface of powdered carbon.  Additional alum was added as well; alum helps clump together algae and other particles in water, facilitating their removal by settling or filtration.  Finally, additional chlorine was added to the treatment process to promote the chemical degradation of the microcystins.

Outsmarting Microcystin

For water treatment operators, the key to removing microystin from water is understanding that the toxin is contained within Microcystis cells.  A treatment process that removes cells without rupturing them, therefore, could help remove microcystin efficiently.  Any treatment process that opens algae cells, on the other hand, releases the toxin in the water.  The World Health Organization recommends various types of filtration to remove microcystis.

Even better than dealing with microcystin successfully at the water treatment plant is not having to deal with it at all.  Microcystis blooms in surface waters can be partially controlled by reducing nutrient pollution from wastewater and land sources.  Controlling soil erosion in the watershed and promoting proper use of manure and fertilizer could go a long way toward avoiding the types of water emergencies that Toledo residents will not soon forget.

Joan B. Rose, PhD, is the Homer Nowlin Chair in Water Research at Michigan State University and a member of the Water Quality and Health Council.