Microcystin, one of the major toxins produced by harmful algal blooms (HABs) has been implicated in a number of health issues, from skin rashes to liver and nervous system damage. A main focus of preventing these negative health impacts has been limiting exposure to contaminated water, but researchers at The Ohio State University have been looking at things from a different angle: microcystin exposure from food.
Lake Erie fish like walleye and yellow perch often swim through algal blooms, breathing in potentially contaminated water through their gills and eating up smaller critters that in turn may have been exposed to toxin. And produce grown along the Lake Erie shoreline – the Maumee River watershed is largely agriculture, after all – may well have been watered with surface water, either from the lake itself or from smaller lakes and streams that also contain cyanobacteria, the organisms that cause harmful algal blooms.
What isn’t known so well is whether those fish and vegetables actually retain any of the algal toxin they are exposed to, and if they do, whether those toxin concentrations are high enough to be of concern. Researchers Drs. Jay Martin, Stu Ludsin and Jiyoung Lee, with funding from Ohio Sea Grant and the Ohio Department of Higher Education’s Harmful Algal Bloom Research Initiative (HABRI), have been working on addressing those questions for the past few years, and so far results have shown that in both cases there is some toxin accumulation, but no reason to completely avoid consumption.
“An important result that really needs to be emphasized based on this work is that while we did find microcystin in these fish, they’re not at a level that impacts public health,” explains Martin, professor in Ohio State’s Department of Food, Agricultural and Biological Engineering. “If anglers and the public abide by the advisories that are sent out from the Ohio Environmental Protection Agency, which are usually about one fish meal per week, then they’re going to be fine.”
Led by Master’s student David Witiszinski, the researchers started with a method most commonly used to detect microcystin in fish tissue, a technique called enzyme-linked immunosorbent assay (ELISA). They found relatively high levels of the toxin in their walleye, yellow perch and white perch samples, but some previous studies suggested that using ELISA to quantify this algal toxin in fish may lead to false positive results and indicate higher concentrations than are actually present in the fish.
So the next step was to develop a procedure to use liquid chromatography tandem-mass spectrometry (LC-MS/MS) with the fish samples, as that method has been shown to offer more reliable results than ELISA in identifying specific types, or congeners, of microcystin. With the help of post-doctoral researcher Manjunath Manubolu and Dr. Ken Riedl, associate director of Ohio State’s Food Innovation Center, the scientists are now able to quantify nine different types of algal toxins from fish tissue samples, including some of the most abundant and most toxic forms of microcystin.
“We’ve used that procedure to process samples from Lake Erie and Grand Lake St. Marys for the Ohio Environmental Protection Agency and the Ohio Department of Natural Resources, so the state is already benefiting from the development of this method,” said Ludsin, associate professor and co-director of Ohio State’s Aquatic Ecology Laboratory.
The team is also working with a testing method called MMPB to quantify total microcystin in tissue samples (instead of detecting specific types that may not add up to total microcystin concentrations with the LC-MS/MS method). That approach allows agencies like the Ohio Environmental Protection Agency to issue any needed drinking water warnings based on a conservative estimate of potential toxicity, while the more detailed analysis by type offers information specifically about some of the most toxic forms of microcystin.
While Ludsin’s lab focused on analyzing fish samples, Lee and doctoral student Seungjun Lee grew three types of vegetables – lettuce, carrots and green beans – while watering them with microcystin-contaminated water at different concentrations. Once harvested, they used ELISA to determine not just how much microcystin was present in those plant samples, but also where exactly the toxin was present: did it accumulate more in the roots, or the leaves, or possibly more in the soil surrounding the plant?
“We found that green beans accumulate more than carrots, and both accumulate more than lettuce,” Lee summarized. “And then it looks like there is generally more toxin in the roots, and that makes sense because we water around the root area.”
Total toxin accumulation isn’t the end result when it comes to public health impacts though. The researchers also calculated health risk based on a number of factors, including data on average monthly consumption for adults and children. They found that, when it comes to health risk, contaminated lettuce is actually of more concern than contaminated carrots, because on average, people tend to eat more lettuce and therefore take in more of any accumulated pollution from that.
In addition to toxin accumulation in both plants and the soil surrounding them, Lee and her team found that microcystin exposure can stunt plant growth, distort shape and cause yellowing, making the vegetables less valuable as commercial crops.
So what can be done about this specific contamination while research continues to try to solve the overall harmful algal bloom problem in Lake Erie? For agriculture, Lee suggests finding an alternative source of water for irrigation. Most large farms already use groundwater in their operations, while smaller farms tend to use more surface water, which can lead to microcystin contamination during bloom season. In those cases, regular water testing and switching to alternative water sources is essential to reduce or prevent exposure that can lead to microcystin contamination. If the toxin is found in soil, rotating cropland gives the toxin time to degrade before planting new crops.
Though fish are unlikely to avoid exposure to microcystin while they’re in the lake, anglers and other consumers don’t have to worry too much about toxin exposure from eating them. Fish can metabolize toxins like microcystin via the liver, which means that unless toxin concentrations are so high that the liver becomes overloaded, the edible muscle tissue is unlikely to contain levels high enough for concern beyond normal fish consumption advisories.
“What we don’t know yet is whether these fish are really taking in toxin but the liver is handling it, or if they’re not taking it in at all,” Ludsin said. “We don’t have that data yet, but we will look at exposure to see whether fish are taking in toxin but handling the load or if they’re just not living in areas where there are blooms.”
Results from fish caught in 2015 so far show that out of 73 analyzed fish, only six showed detectable levels of microcystin in edible tissues, which don’t include the liver and other organs, and those levels were still well below consumption limits. “So if a person follows the guideline of no more than one fish meal per week, there would be no concern of getting any sort of toxicity from consuming the edible fraction of either walleye or yellow perch,” Ludsin concluded.
And of course, while some scientists are focusing on the impacts of harmful algal blooms on everything from food to recreational opportunities, research also continues to help address the algal blooms themselves. The Harmful Algal Bloom Research Initiative (HABRI), funded by the Ohio Department of Higher Education and managed by Ohio Sea Grant, connects research teams across the state and beyond to find new approaches to reducing harmful algal blooms in Lake Erie, using input from stakeholders that range from state agencies to local farmers.