Hexbyte Glen Cove Researchers find how tiny plastics slip through the environment thumbnail

Hexbyte Glen Cove Researchers find how tiny plastics slip through the environment

Hexbyte Glen Cove

Credit: Pixabay/CC0 Public Domain

Washington State University researchers have shown the fundamental mechanisms that allow tiny pieces of plastic bags and foam packaging at the nanoscale to move through the environment.

The researchers found that a silica surface such as sand has little effect on slowing down the movement of the plastics, but that natural organic matter resulting from decomposition of plant and animal remains can either temporarily or permanently trap the nanoscale particles, depending on the type of plastics.

The work, published in the journal Water Research, could help researchers develop better ways to filter out and clean up pervasive plastics from the . The researchers include Indranil Chowdhury, assistant professor in WSU’s Department of Civil and Environmental Engineering, along with Mehnaz Shams and Iftaykhairul Alam, recent graduates of the civil engineering program.

“We’re looking at developing a filter that can be more efficient at removing these plastics,” Chowdhury said. “People have seen these plastics escaping into our , and our current drinking water system is not adequate enough to remove these micro and nanoscale plastics. This work is the first fundamental way to look at those mechanisms.”

Around since the 1950s, plastics have properties that make them useful for modern society. They are water resistant, cheap, easy to manufacture and useful for a huge variety of purposes. However, plastics accumulation is becoming a growing concern around the world with giant patches of plastic garbage floating in the oceans and plastic waste showing up in the most remote areas of the world.

“Plastics are a great invention and so easy to use, but they are so persistent in the environment,” Chowdhury said.

After they’re used, plastics degrade through chemical, mechanical and biological processes to micro- and then nano-sized particles less than 100 nanometers in size. Despite their removal in some , large amounts of micro and nanoscale plastics still end up in the environment. More than 90% of tap water in the U.S. contains nanoscale plastics, Chowdhury said, and a 2019 study found that people eat about five grams of plastic a week or the amount of plastic in a credit card. The health effects of such environmental pollution is not well understood.

“We don’t know the health effects, and the toxicity is still unknown, but we continue to drink these plastics every day,” said Chowdhury.

As part of the new study, the researchers studied the interactions with the environment of the tiniest particles of the two most common types of plastics, polyethylene and polystyrene, to learn what might impede their movement. Polyethylene is used in plastic bags, milk cartons and food packaging, while polystyrene is a foamed plastic that is used in foam drinking cups and packaging materials.

In their work, the researchers found that the polyethylene particles from plastic bags move easily through the environment—whether through a silica surface like sand or natural organic matter. Sand and the plastic particles repel each other similarly to like-poles of a magnet, so that the plastic won’t stick to the sand particles. The do glom onto natural organic material that is ubiquitous in natural aquatic environment but only temporarily. They can be easily washed off with a change in chemistry in the water.

“That’s bad news for polyethylene in the environment,” said Chowdhury. “It doesn’t stick to the silica surface that much and if it sticks to the natural organic matter surface, it can be re-mobilized. Based on these findings, it indicates that nanoscale polyethylene plastics may escape from our drinking water treatment processes, particularly filtration.”

In the case of polystyrene particles, the researchers found better news. While a silica surface was not able to stop its movement, organic matter did. Once the polystyrene particles stuck to the organic matter, they stayed in place.

The researchers hope that the research will eventually help them develop filtration systems for treatment facilities to remove nanoscale particles of plastics.



More information:
Mehnaz Shams et al, Interactions of nanoscale plastics with natural organic matter and silica surfaces using a quartz crystal microbalance, Water Research (2021). DOI: 10.1016/j.watres.2021.117066

Citation:
Researchers find how tiny plastics slip through

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Hexbyte Glen Cove Biochar from agricultural waste products can adsorb contaminants in wastewater

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Lead researcher Marlena Ndoun, a doctoral student in Penn State’s Department of Agricultural and Biological Engineering, samples water in central Pennsylvania’s Spring Creek for emerging contaminants. Credit: Pennsylvania State University

Biochar—a charcoal-like substance made primarily from agricultural waste products—holds promise for removing emerging contaminants such as pharmaceuticals from treated wastewater.

That’s the conclusion of a team of researchers that conducted a novel study that evaluated and compared the ability of derived from two common leftover agricultural materials—cotton gin and guayule bagasse—to adsorb three common pharmaceutical compounds from an aqueous solution. In adsorption, one material, like a pharmaceutical compound, sticks to the surface of another, like the solid biochar particle. Conversely, in absorption, one material is taken internally into another; for example, a sponge absorbs water.

Guayule, a shrub that grows in the arid Southwest, provided the waste for one of the biochars tested in the research. More properly called Parthenium argentatum, it has been cultivated as a source of rubber and latex. The plant is chopped to the ground and its branches mashed up to extract the latex. The dry, pulpy, fibrous residue that remains after stalks are crushed to extract the latex is called bagasse.

The results are important, according to researcher Herschel Elliott, Penn State professor of agricultural and biological engineering, College of Agricultural Sciences, because they demonstrate the potential for biochar made from plentiful agricultural wastes—that otherwise must be disposed of—to serve as a low-cost additional treatment for reducing in treated wastewater used for irrigation.

“Most are currently not equipped to remove emerging contaminants such as pharmaceuticals, and if those toxic compounds can be removed by biochars, then wastewater can be recycled in irrigation systems,” he said. “That beneficial reuse is critical in regions such as the U.S. Southwest, where a lack of water hinders crop production.”

The pharmaceutical compounds used in the study to test whether the biochars would adsorb them from aqueous solution were: sulfapyridine, an antibacterial medication no longer prescribed for treatment of infections in humans but commonly used in veterinary medicine; docusate, widely used in medicines as a laxative and stool softener; and erythromycin, an antibiotic used to treat infections and acne.

The results, published today (Nov. 16) in Biochar, suggest biochars made from agricultural waste materials could act as effective adsorbents to remove pharmaceuticals from prior to irrigation. However, the biochar derived from cotton gin waste was much more efficient.

In the research, it adsorbed 98% of the docusate, 74% of the erythromycin and 70% of the sulfapyridine in aqueous solution. By comparison, the biochar derived from guayule bagasse adsorbed 50% of the docusate, 50% of the erythromycin and just 5% of the sulfapyridine.

The research revealed that a temperature increase, from about 650 to about 1,300 degrees F in the oxygen-free pyrolysis process used to convert the agricultural waste materials to biochars, resulted in a greatly enhanced capacity to adsorb the pharmaceutical compounds.

“The most innovative part about the research was the use of the guayule bagasse because there have been no previous studies on using that material to produce biochar for the removal of emerging contaminants,” said lead researcher Marlene Ndoun, a doctoral student in Penn State’s Department of Agricultural and Biological Engineering. “Same for cotton gin waste—research has been done on potential ways to remove other contaminants, but this is the first study to use cotton gin waste specifically to remove pharmaceuticals from water.”

For Ndoun, the research is more than theoretical. She said she wants to scale up the technology and make a difference in the world. Because cotton gin waste is widely available, even in the poorest regions, she believes it holds promise as a source of biochar to decontaminate water.

“I am originally from Cameroon, and the reason I’m even here is because I’m looking for ways to filter water in resource-limited communities, such as where I grew up,” she said. “We think if this could be scaled up, it would be ideal for use in countries in sub-Saharan Africa, where people don’t have access to sophisticated equipment to purify their water.”

The next step, Ndoun explained, would be to develop a mixture of biochar material capable of adsorbing a wide range of contaminants from water.

“Beyond removing emerging contaminants such as pharmaceuticals, I am interested in blending biochar materials so that we have low-cost filters able to remove the typical contaminants we find in , such as bacteria and organic matter,” said Ndoun.



More information:
Marlene C. Ndoun et al, Adsorption of pharmaceuticals from aqueous solutions using biochar derived from cotton gin waste and guayule bagasse, Biochar (2020). DOI: 10.1007/s42773-020-00070-2

Citation:
Biochar from agricultural waste products can adsorb contaminants in wastewater (2020, November 16)
retrieved 17 November 2020
from https://phys.org/news/2020-11-biochar-agricultural-products-adsorb-contaminants.html