Can exposing harmful algal blooms and their associated toxins to ultraviolet light work as an effective drinking water treatment? A team of researchers at The Ohio State University, funded by the Harmful Algal Bloom Research Initiative (HABRI), recently put this idea to the test.
Toxin-producing harmful algal blooms or cyanobacteria present a human health concern for Great Lakes communities due to potential impacts on drinking water. Scientists have studied how to improve water treatment strategies to account for these cyanotoxins, yet each method presents tradeoffs. In search of a treatment tool without tradeoffs, researchers are studying a new technique: exposing harmful algal blooms to UV light.
For the experiments, researchers collected samples of several different algal toxins found in bodies of Ohio freshwater and placed them under a UV lamp, pictured here.
The researchers, led by Dr. Natalie Hull of Ohio State’s College of Engineering, hypothesized that exposure to UV light near wavelengths of 222 nanometers showed greater promise in treating and degrading algal toxins compared to wavelengths near 254 nanometers, used in previous studies.
“It’s important to seek new methods for water treatment plants to protect population health with strategies that are both effective and efficient,” Hull said. “Different costs, efficiencies, and byproducts are associated with different water treatment methods, whether used alone or in combination.”
The team aimed to understand if UV light would cause toxins to degrade and whether such light exposure would cause cells to produce or release more or fewer toxins. These factors are important considerations in water treatment to ensure communities are provided with safe drinking water.
Through the project, researchers exposed four different toxins and four different cyanobacteria to two lamps emitting either 222- or 254-nanometer wavelength UV light. Toxins included common varieties found in bodies of Ohio freshwater: microcystin, anatoxin, cylindrospermopsin, and saxitoxin.
After light exposure, all four toxins were measured using a fairly standard lab test (enzyme-linked immunosorbent assay, or ELISA), and all four cyanobacteria were measured for specific parameters.
This work found that microcystin was more effectively broken down by UV than the other three toxins. Further, results showed that the impact of UV on cyanobacteria is dependent on bacteria strain, UV wavelength, and dose — or the amount of energy absorbed. The 222-nanometer lamp was observed to be 2.4 to 4.2 times more effective at degrading microcystin and resulted in lower toxic activity than exposure to the 254-nanometer lamp. The impact of UV on cyanobacteria was measured to be dependent on the wavelength and dose the cells were exposed to.
“It was interesting to see how important cyanotoxin structure and UV wavelength played in the efficiency of the water treatment,” Hull said. “Further research is needed to understand the full scope of cellular impacts.”
These insights will help inform water treatment plants that UV treatment is beneficial to implement when microcystin is present, but additional considerations may need to be made for other toxins and different cyanobacteria.
Ohio Sea Grant is supported by The Ohio State University College of Food, Agricultural, and Environmental Sciences (CFAES) School of Environment and Natural Resources, Ohio State University Extension, and NOAA Sea Grant, a network of 34 Sea Grant programs nation-wide dedicated to the protection and sustainable use of marine and Great Lakes resources. Stone Laboratory is Ohio State’s island campus on Lake Erie and is the research, education, and outreach facility of Ohio Sea Grant and part of CFAES School of Environment and Natural Resources.