Using two different measurement methods, researchers from North Carolina State University conducted a two-year study of North Carolina's Jordan Lake in which they monitored toxic algal blooms. The researchers found that multiple cyanotoxins from toxic algal blooms are present year-round, albeit in very low concentrations. Their findings could improve the ability to predict toxic blooms.

Freshwater algal blooms have increased due to nutrients from sources such as fertilizers and other agricultural runoff entering the water. While every algal bloom isn't toxic -- some algal species can produce both toxic and nontoxic blooms -- toxic blooms can cause problems for swimmers and other recreational users in the form of rashes or allergic reactions.

"We've confirmed both that the toxins are there year-round and that multiple toxins are there simultaneously but in very low levels," says Astrid Schnetzer, associate professor of marine, earth and atmospheric sciences at NC State and corresponding author of a paper describing the research. "First, let's be clear that the presence of the toxins doesn't affect drinking water -- treatment plants scrub all of that out. Secondly, the amounts of toxins we did find are about an order of magnitude below safe levels, so that's also good news."

Schnetzer and former NC State graduate student Daniel Wiltsie wanted to know which cyanotoxins were present in Jordan Lake, a major drinking water reservoir in central North Carolina.

From 2014-16 Schnetzer and Wiltsie sampled the lake water in two ways: by taking discrete samples (in which water is collected in a container) and by using solid phase adsorption toxin tracking (SPATT) bags, which are left in the water for a period of days or weeks. SPATT bags contain an absorbent resin that captures dissolved toxins. "By using two methods we were better able to determine what the concentrations looked like over time," Schnetzer says. "Algal blooms are ephemeral, so it's possible to completely miss them if you only look at discrete sampling. SPATT bags give you data on how the toxins can accumulate and overlap."

The researchers analyzed the samples for five different toxins, and found four of them: microsystin, anatoxin-a, clindrospermopsin, and ?-N-methylamino-L-alanine (BMAA). Multiple toxins were detected at 86 percent of the sampling sites and during 44 percent of the sampling events.

"This study is the first to use both SPATT bags and sampling to assess the toxins in the water," Schnetzer says. "It's a first step toward creating better informed approaches to really understanding the frequency and magnitude of these blooms.

"In the future, we want to have a better predictive capability regarding these blooms as well as the ability to identify new emerging toxins. The data may also help us determine risk from chronic low-level exposures, as well as tease out what risks derive from exposure to multiple toxins at once."