Toxic blue-green algae a growing threat to nation’s drinking, recreational water

“The biggest health concern with cyanobacteria in sources of drinking water is that there’s very little regulatory oversight, and it remains unclear what level of monitoring is being voluntarily conducted by drinking water utilities,” said Tim Otten, a postdoctoral scholar in the OSU Department of Microbiology, and lead author on the study.

“At this point we only have toxicology data for a handful of these toxins, and even for those it remains unclear what are the effects of chronic, low-dose exposures over a lifetime,” Otten said. “We know some of the liver toxins such as microcystin are probable carcinogens, but we’ve really scratched only the surface with regard to understanding what the health effects may be for the bioactive metabolites produced by these organisms.”

Otten referred to the “precautionary principle” of protecting human health before damage is done.

“In my mind, these bacteria should be considered guilty until proven innocent, and in drinking water treated as potential pathogens,” he said. “I think cyanobacteria should be approached with significant caution, and deserve better monitoring and regulation.”

The issue is complex, because not all cyanobacteria are a problem, and in fact they play many positive roles as primary producers in oceans and fresh waters. They are among Earth’s oldest life forms, and more than two billion years ago helped produce much of the oxygen that made much other life on Earth possible, including humans. But various strains of them have likely always been toxic.

Scientists said a concern is that nutrient over-enrichment may select for the more toxic populations of these bacteria, creating a positive feedback loop that makes the problem even worse.

Researchers said in their analysis that modern water treatment does a reasonably good job of making drinking water safe, but the lack of required or widespread monitoring remains a problem. No one should drink untreated surface water that may be contaminated by cyanobacteria, and another serious concern is recreational exposure through swimming or other water sports.

Cyanobacteria-associated illnesses are not required to be reported under the Center for Disease Control and Prevention’s guidelines, as most pathogens are. This makes accurate assessments of the incidence and severity of adverse health outcomes difficult to determine.

A recent study identified eleven freshwater lake, algal-bloom associated disease outbreaks, and sixty-one illnesses in 2009-10, based on reports from New York, Ohio, and Washington. The most common symptoms were skin rashes and gastroenteritis. There were no fatalities.

Many large, eutrophic lakes such as Lake Erie are plagued each year by algal blooms so massive that they are visible from outer space. Dogs have died from drinking contaminated water, and sea otter deaths in Monterey Bay have been attributed to them eating shellfish contaminated with microcystin that came from an inland lake.

Until better monitoring standards are in place, the researchers note, an unfortunate indicator of toxic algal bloom events will be illness or death among pets, livestock and wild animals that drink contaminated water.

One cannot tell visually if an algal bloom will be toxic or not, Otten said, and traditional microscopic cell counting and other approaches to assess risk are too slow for making time-sensitive, public health decisions. But the future holds promise. New DNA-based techniques can be used by experts to estimate health risks faster and cheaper than traditional methods.

Cyanobacterial toxins are not destroyed by boiling. However, individuals concerned about the safety of their drinking water may use regularly-changed point-of-use carbon filtration devices that are effective in reducing these health risks.

People should also develop an awareness of what cyanobacteria look like, in a natural setting appearing as green, paint-like surface scums. They should avoid water recreation on a lake or river that has these characteristics, researchers said.

— Read more in Timothy G. Otten, Hans W. Paerl, “Health Effects of Toxic Cyanobacteria in U.S. Drinking and Recreational Waters: Our Current Understanding and Proposed Direction,” Current Environmental Health Reports 2, no. 1 (March 2015): 75-84 (DOI: 10.1007/s40572-014-0041-9)