Human-caused environmental problems cause increase in toxic algal blooms
Oct. 30, 2013
Nutrient enrichment and climate change are posing yet another concern of growing importance – an apparent increase in the toxicity of some algal blooms in freshwater lakes and estuaries around the world, which threatens aquatic organisms, ecosystem health and human drinking water safety.
As this nutrient enrichment increases, coupled with warmer temperatures, drought, and other climate-caused factors, so will the proportion of toxin-producing strains of cyanobacteria in harmful algal blooms, scientists said.
Researchers from The University of North Carolina at Chapel Hill’s Gillings School of Global Public Health and the University of Oregon outlined their recent findings in a perspective article, published online Oct. 25 in the journal Science.
Authors of the article were William R. Kenan Distinguished Professor Hans W. Paerl, PhD, professor of environmental sciences and engineering in the Gillings School and of marine sciences at UNC’s Institute of Marine Sciences, based in Morehead City, N.C., and Timothy Otten, PhD, postdoctoral scholar in the College of Science and College of Agricultural Sciences at Oregon State University.
Cyanobacteria are some of the oldest microorganisms on Earth, dating back about 3.5 billion years to a time when the planet was void of oxygen and barren of most life. The bacteria, which derive their energy through photosynthesis, are believed to have produced the oxygen that paved the way for terrestrial life to evolve. They are highly adaptive and persistent, researchers say, and now are adapting to new conditions in ways that threaten some of the life they originally made possible.
Of particular concern is Microcystis sp., a near-ubiquitous cyanobacterium that thrives in warm, nutrient-rich and stagnant waters around the world. Like many cyanobacteria, it can regulate its position in the water column, and often forms green, paint-like scums near the surface.
In a high-light, oxidizing environment, microcystin-producing cyanobacteria have a survival advantage over other forms of cyanobacteria that are not toxic. Over time, they can displace the nontoxic strains, resulting in blooms that are increasingly toxic.
“Cyanobacteria are basically the cockroaches of the aquatic world,” said Otten, “When one considers that they’ve persisted even through ice ages and asteroid strikes, it’s not surprising they’re extremely difficult to remove once they’ve taken hold in a lake,” he said. “For the most part, the best we can do is to try to minimize the conditions that favor their proliferation.”
Based on the last Environmental Protection Agency National Lakes Assessment, at least one-third of the United States’ 123,000 lakes may contain toxin-producing cyanobacteria. Dams, rising temperatures and carbon dioxide concentrations, droughts, and increased runoff of nutrients from urban and agricultural lands are compounding the problem.
Many large lakes, including 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.
Researchers doubt that the primary function of cyanobacteria is to be toxic, as they had no predators when they came into being. New research suggests that the potent liver toxin and possible carcinogen, microcystin, has a protective role in cyanobacteria and helps them respond to oxidative stress. This is probably one of the reasons the genes involved in its biosynthesis are so widespread across cyanobacteria and have been retained over millions of years.
Because of their buoyancy and the location of toxins primarily within the cell, exposure risks are greatest near the water’s surface, which raises concerns for swimming, boating and other recreational uses. Also, since cyanobacteria blooms become entrenched and usually occur every summer in impacted systems, chronic exposure to drinking water containing these compounds is an important concern that needs more attention.
“Water quality managers have a toolbox of options to mitigate cyanobacteria toxicity issues, assuming they are aware of the problem and compelled to act,” Otten said. “But there are no formal regulations in place on how to respond to bloom events.”
The authors conclude that public awareness should be raised about these issues. Given a warming climate, rising carbon dioxide levels, dams on many rivers and overloading of nutrients into our waterways, the magnitude and duration of toxic cyanobacterial blooms will only worsen.
Original release by Oregon State University