If you live near a lake in the U.S., you may have noticed signs warning of toxic blue-green algae, or cyanobacteria. Such warnings, advising swimmers and boaters to stay out of the water, and keep pets away as well, are becoming increasingly common as the thick, green muck appears on once-pristine waterways. Blue-green algae make up a portion of the phytoplankton in many bodies of water, and they're not inherently dangerous or even altogether unusual.
According to the Wisconsin Department of Natural Resources (DNR), fossil evidence suggests blue-green algae have been around for millions of years, with algal blooms dating back to the 12th century. However, the agency notes, "[I]t is possible that the frequency and duration of blooms are increasing in some Wisconsin waters as a result of increased nutrient concentrations."
The problem of increasing algal blooms is not unique to Wisconsin — it's happening all over the U.S., particularly in agricultural areas where the use of phosphorus-based fertilizers is prolific.
Phosphorus is a known driver of blue-green algae, as they use it readily for fuel. Researchers have uncovered another, relatively surprising, source of phosphorus that also appears to be driving the toxic algae growth to unprecedented levels — glyphosate, the active ingredient in Roundup herbicide.
Glyphosate May Be Driving Up Rates of Toxic Algae
Glyphosate is a synthetic phosphonate herbicide and is the most heavily used agricultural chemical of all time. In the U.S., over 1.6 billion kilograms of the chemical have been applied since 1974. It was long believed that plankton could not access phosphonates like glyphosate as a fuel source, but in 2009 R. Michael McKay and George Bullerjahn of Bowling Green State University in Ohio showed that this is not the case.
Instead, they found that cyanobacteria can utilize the phosphonate portion of the glyphosate molecule. In a report released by the Ohio Environmental Protection Agency (EPA) — the Ohio Lake Erie Phosphorus Task Force Final Report — it's stated, "The researchers estimate that as much as 1,000 metric tons [about 2.2 million pounds] of Roundup is applied to Lake Erie's watershed per year, and it is being detected in adjacent waterways particularly in the spring." Bullerjahn further stated in an Ohio State University news release:
"It turns out that many cyanobacteria present in Lake Erie have the genes allowing the uptake of phosphonates, and these cyanobacteria can grow using glyphosate and other phosphonates as a sole source of phosphorus."
Lake Erie has been struggling with algae blooms due to manure, sewage and fertilizer runoff, as well as runoffs from glyphosate applications, leading to contaminated drinking water and fish die-offs for decades. Algae-triggered "dead zones" in the lake are now larger than they've been since the '80s and cover 25 percent of the entire lake. Further, in 2017 the lake's algal blooms were recorded as the third-largest on record.
Spikes in Phosphorus in Lake Erie Watershed Linked to Planting of GE Crops
Adding to the evidence that could be playing a role is research by Ohio Northern University chemist Christopher Spiese and colleagues, who suggested that spikes in dissolved reactive phosphorus (DRP) runoff that have increased since the mid-1990s coincided with an increased use of glyphosate.
At the 2016 Conservation Tillage and Technology Conference, Spiese shared the results of his study, which found a significant correlation between DRP loads and the number of acres planted with herbicide-tolerant genetically engineered (GE) crops (which are heavily sprayed with ). "For every acre of Roundup Ready soybeans and corn that you plant, it works out to be about one-third of a pound of P coming down the Maumee [watershed and into Lake Erie]," Spiese told Sustainable Pulse.
Spiese also found that glyphosate is capable of releasing phosphorus from the soil and conducted studies to see what happens when soil samples were applied with phosphorus and then sprayed with glyphosate. Some of the samples showed significant phosphorus release, with "hot spots" likely contributing a significant amount of DRP. Sustainable Pulse reported:
"Based on the average two glyphosate applications growers make every year, Spiese estimates that overall, 20-25% of the DRP runoff is caused by glyphosate. But depending on the location within the watershed, that percentage could be much lower or much greater."
In February 2016, the U.S. and Canada announced plans to reduce the amount of phosphorus entering Lake Erie by 40 percent by 2025, but it's seeming increasingly clear that reaching this goal must take into account not only fertilizer runoff but also glyphosate applications. The problem has gotten so bad in the area that even drinking water has been affected.
In 2014, citizens in Toledo, Ohio, were warned not to drink their tap water as it was found to contain significantly elevated levels of microcystins, caused by algae blooms in Lake Erie. Microsystins are nerve toxins produced by some blue-green algae that can cause fever, , vomiting and seizures.
The city and surrounding areas became the first to report drinking water-associated outbreaks caused by harmful algal blooms, as highlighted in the U.S. Centers for Disease Control and Prevention's (CDC) November 2017 surveillance for waterborne disease outbreaks report.
"The cyanobacterial toxin microcystin caused the largest reported toxin contamination of community drinking water in August 2013 and September 2014 and was responsible for extensive community and water disruptions," the CDC noted. The agency is now tracking harmful algal blooms (HABs) via its One Health Harmful Algal Bloom System (OHHABS), calling them an "emerging public health issue."