Growing up in southern India, Rajani Srinivasan knew that okra was delicious when cut up and served in bhindi masala. It was also common knowledge that tamarind enlivened a vegetable curry and that dried fenugreek leaves filled the kitchen with a bittersweet aroma. But it wasn’t until decades later that Srinivasan made an unlikely and promising new discovery about these staples of her native cuisine.
With her team of researchers, Srinivasan, now a professor of chemistry at Tarleton State University, has found that these ingredients can remove microplastics from water, reducing the likelihood that they’ll be consumed, or that they’ll pollute sensitive ecosystems. “I wanted to come up with a unique solution for a bigger problem,” Srinivasan says.
Microplastics, which are tiny plastic fragments no bigger than five millimeters, may splinter off plastic objects—such as shopping bags, water bottles, or PVC pipes—and get swept into culverts, washed into streams, or flushed down bathroom sinks. They can also seep out of products such as toiletries and cosmetics, and they end up seemingly ubiquitous in water supplies across the globe, accumulating in alarming densities and causing health problems for all manner of aquatic animals.
The threats posed by microplastics are not fully understood. They may not be harmful to human health on their own, but they can be vessels for toxins that make their way into virtually every environment on earth, including soils and subsurface groundwater. Studies show that each of us unintentionally consumes tens of thousands of microplastic particles every year.
The most common solution for getting microplastics out of drinking water, though, has its own drawbacks. Many water treatment facilities use synthetic chemical additives called flocculants, which attract microplastics and other suspended solids, causing them to clump together and sink to the bottom, where they can be removed. Yet the chemicals commonly used as flocculants may be toxic. “If we are removing microplastics and in turn adding some materials which are toxic to us, it does not make a lot of sense,” says Srinivasan, who has been working on ways to use plants, foods, and spices to replace synthetic agents since the early aughts, when she was a graduate student studying applied chemistry in Kanpur, a city on the banks of the Ganges River in northern India.
Srinivasan, who took a job at Tarleton State in 2012, began testing extracts of okra, fenugreek, and tamarind—all elements of her regular diet—to see if they might make for good substitutes for synthetic flocculants. Since 2019, she and her students have experimented with different concoctions at their lab in Stephenville, about eighty miles southwest of Fort Worth. Eventually, in 2020, they found a combination that worked as well as, or even better.
During a presentation last month at the American Chemical Society’s spring meeting, Srinivasan detailed the efficacy of these ingredients as a treatment for microplastics contamination. She explained that she and her students used carbohydrates (polysaccharides) drawn from okra and tamarind in equal parts and created a flocculant that isolated and allowed them to remove microplastics from fresh water. For ocean water, they paired carbohydrate extracts from okra and fenugreek. Srinivasan says the results of her tests show that microplastics can be extracted from water using food ingredients instead of synthetic, and potentially harmful, chemical agents.
“I think it seems like a really good idea,” says Susan Bratton, a professor of environmental studies at Baylor University whose research has documented the presence of microplastics in ecosystems throughout Texas. Bratton and one of her students recently published a study that took samples from the Brazos and San Marcos rivers, among other nearby watersheds. At the study’s outset, the researchers hypothesized that samples taken from areas in dense urban centers, or downstream from wastewater discharge points, would contain significantly higher levels of microplastics, but the results were surprising. Even relatively remote stretches of crystal-clear streams, such as the San Marcos River, contained microplastics. “That’s coming out of a huge limestone high-volume spring,” Bratton says. “That’s some of the clearest water in the state.”
Srinivasan has also partnered with the High Plains Water District, based in Lubbock, to test methods of removing other contaminants from groundwater pumped from the Ogalalla and Dockum aquifers. The Dockum aquifer contains arsenic, a mineral associated with cancer. Jason Coleman, general manager of HPWD, says Srinivasan has used plant-based polymers—similar to those created from okra and tamarind—to target dissolved solids like arsenic in groundwater pumped from the High Plains with the intention of binding it so it can be separated from the water. “The deepest of our three aquifers happens to be one that contains more areas of higher total dissolved solids,” Coleman says. “[Srinivasan’s] research on that front has been particularly meaningful for people in our area.”
The plant-based combinations that Srinivasan’s team have developed are ready-made for water treatment plants. Srinivasan says her compounds are interchangeable with chemical flocculants already in use at many facilities. “You do not have to have any new infrastructure built,” she says. “Just replace the synthetic materials that are being used with these materials.”
With states like California prioritizing organic materials for the removal of contaminants, it’s really only a matter of time before products such as Srinivasan’s okra-tamarind concoction are in widespread use, she insists. Indeed, in Dallas, despite wastewater treatment facilities not being required by state regulators to remove microplastics, the city says it has begun studying microplastic removal techniques with the expectation that removing them may eventually be required. Meanwhile, a 2019 World Health Organization found that traditional wastewater treatments eliminate 90 percent of microplastics already, and Bratton says the wastewater treatment sites her researchers monitored were not discharging many microplastics.
Srinivasan’s research has yet to be published in a peer-reviewed journal, and any potential food-based flocculant will need to clear licensing hurdles, not to mention be marketed to water treatment specialists. But Srinivasan is already working on ways to quickly scale up the removal process, and she hopes to partner soon with companies that can handle large-scale production of the necessary polysaccharides.
Srinivasan calls for one gram of her polysaccharide combination per one liter of water, and given that many major municipal water operations treat tens of billions of gallons annually, it’s possible that widespread adoption of her solution could spark boom markets in okra and tamarind, similar to the way corn production shot up dramatically after ethanol standards were adopted. “The potential is there,” says Rodolfo Nayga, head of Texas A&M’s department of agricultural economics, “for the okra market to expand just like corn.”