Toxic bacteria blooms are affecting public drinking water systems across Iowa, according to a survey by the state's Department of Natural Resources. But data shows utilities are capable of handling current levels of these toxins, called microcystins.
Toxic chemicals called microcystins that are produced by cyanobacteria showed up in the raw water supplies of 15 out of 26 public water systems tested by the Iowa Department of Natural Resources.
"The study demonstrates that Iowa does have the potential for microcystin occurrence in its source water over all regions of the state," the study authors wrote.
Researchers were testing for microcystins at levels of .3 µg/L, or micrograms per liter, which is equivalent to .3 parts per billion. At that level, the U.S. Environmental Protection Agency recommends infants, children under five years old and pregnant women not drink the water. The toxins can cause liver and kidney damage and cancer.
"Lower microcystin levels were found in this study as compared to historical results of the DNR’s state park swimming beach ambient water monitoring data, which have exceeded total microcystin levels of 20 [parts per billion] at times," the authors wrote.
The highest levels of microcystin researchers detected in raw water exceeded 5 parts per billion. But researchers didn’t find any detectable levels of microcystins in the treated tap water Iowans drink, called "finished water." The DNR's Diane Moles oversaw the survey.
“Yes it’s found in the waters around the state. So ‘being at risk’ is probably a term that carries a little more emphasis than it could be," Moles said. "But the possibility is there.”
The survey shows surface waters like rivers, lakes and reservoirs are especially at risk. That’s important because many Iowans rely on drinking water that comes from surface water, or on what's known as influenced ground water, or water that's taken from shallower wells that are directly impacted by surface water, such as a well located near a river or lake.
“And that serves about 45 percent of the population," Moles said. "So it’s a small number of systems but they serve some of the larger population areas.”
The cities of Des Moines, Davenport and Iowa City rely on surface water, while Cedar Rapids and Sioux City rely on influenced groundwater. Other communities like Ames, and many individual homeowners, rely on groundwater from wells, which draw on water deep underground that's naturally percolated and filtered through layers of soils, sands and rocks. Many municipal water systems rely on different combinations of surface water, groundwater or influenced groundwater.
Not all cyanobacteria blooms produce the harmful microcystins, and scientists aren't sure why that is. But research shows blooms themselves are spurred by nutrients like phosphorus and nitrogen that flow off of farmfields and into waterways. Warm weather is also a factor, and blooms are more common in the spring and summer months.
Besides testing for microcystins, researchers also monitored pH levels, water temperature, and turbidity, or water clarity, but they did not test for nutrients.