How electrochemical sensors may help warn of future harmful algal blooms

Posted: December 3, 2021

Electrochemical signals associated with microbial activities could indicate processes that enhance or limit phosphate release

sc-zra technique

By: Allie Fehr

On August 2, 2014, the cautionary words “DO NOT DRINK THE WATER” opened the City of Toledo’s public safety notice.  

Toxins from a harmful algal bloom (HAB) had contaminated western Lake Erie, forcing the city to suspend drinking of the treated lake water for three days due to uncertainties about the information on toxins in treated water and their effect on human health. The shutdown not only had economic consequences but also created public mistrust surrounding water treatment.  

Years after the Toledo Water Crisis, HABs continue to threaten Ohio’s water quality.   

HABs form when there are high levels of nutrients such as phosphorus and nitrogen in a body of water. An increased accumulation of phosphorus in water, also known as phosphorus loading, can heighten the severity of HABs. Despite continuous efforts to manage external loads of phosphorus — the runoff of phosphorus on land from fertilizers and other sources into bodies of water — HAB’s severity in freshwaters remains unchanged.  

green water

Another understudied source of phosphorous in water is internal phosphorus loading — the release of phosphorus (generally as phosphate) from sediments on a water body’s floor. However, the potential for and extent of internal phosphorus loading is difficult to monitor.  

In a project funded by the Ohio Water Resources Center, two researchers intend to address the issue of monitoring internal phosphorous loading by investigating how electrochemical sensors could help track the release of phosphate from sediments in Lake Erie.  

Dr. John Senko, Associate Professor in the Department of Geosciences and Biology at the University of Akron, and Dr. Chelsea Monty-Bromer, Associate Professor of Chemical and Biomedical Engineering at Cleveland State University, are asking whether electrochemical signals associated with microbial activities in benthic sediments could indicate the microbiological processes that enhance or limit phosphate release from sediments.  

After talking to people who work in water monitoring, Monty-Bromer said they have a hard time predicting when internal phosphate is released and knowing what the processes are that cause it to happen. The researchers’ goal for their project is to develop a sensor system positioned in lake sediments that could serve as an early warning system for the severity of HABs resulting from internal phosphate loading.  

In their research, Senko and Monty-Bromer are using an electrochemical split-chamber zero resistance ammetry (SC-ZRA) sensing technique that allows them to detect varying microbiological activities in sediments, without influencing the native biology, based on electrochemical signatures. 

“It’s a way that we can non-destructively, non-invasively listen to what’s going on in the sediment and then use that and use those signatures to predict what kinds of microorganisms are there or what processes might be taking place,” Monty-Bromer said.  

With the SC-ZRA technique, the researchers are particularly interested in looking at iron reduction. 

“A lot of the organisms that are electrochemically active are organisms that can essentially breathe iron, and iron transformations can control the availability of phosphate,” Senko said. “We thought maybe this is a way that we can detect the activities of iron-reducing bacteria, which in turn could control phosphate release or sequestration of the phosphate from the water.” 

The research process kicked into motion around November 2020 when Senko and Monty-Bromer students collected their first samples of sediment from Old Woman Creek estuary on Lake Erie, subsequently analyzing their water chemistry and the types of organisms growing there.  

green water

With this information, the researchers are able to mimic the real-life environment in a lab and deploy the SC-ZRA technique by conducting split chamber incubations with sediment in each chamber. Manipulation of microbial activities, such as adding or removing oxygen, is administered to either or both chambers. The team can then monitor the resulting patterns of current and voltage from these microbial activities that adjust the flux of phosphorus from phosphorus-loaded sediments.  

“We see what kinds of microbial communities start to develop in response to us poking and prodding them chemically,” Senko said.  

Similar to many other projects, the pandemic had put a pause on the team’s research. Although they would have preferred to proceed with their work, Monty-Bromer said that the time spent away from the lab and planning instead allowed them to improve their narrative and goals. 

While the research has generally been exploratory, Senko said they have used their results thus far to design sensors that they believe will be field-deployable and hope to put them into practice in a real environment next summer. With tools such as these, they aim to provide insight and clarity to water monitors for issues such as remnant phosphate that currently cannot be completely accounted for.