Silver nanoparticles are being added to a growing number of everyday consumer products, with many inevitably finding their way into the environment. A new study examines whether living bacterial biofilms can help with their removal during the wastewater treatment process.
Nowadays, manufacturers are incorporating engineered nanoparticles into thousands of products – such as cosmetics, sunscreens, clothing and food packaging – to enhance their existing properties or add new benefits, such as an improved texture or a longer shelf-life. Silver nanoparticles (Ag-NPs) are one of the largest and fastest growing categories, due to their powerful anti-microbial properties and relatively low cost.
But a large proportion of these tiny particles are inevitably released into wastewater, with many ultimately ending up in the environment. Here, they can accumulate in crops and aquatic life, with potential knock-on implications from their subsequent transfer through the food chain. Innovative approaches will be necessary to tackle this new man-made threat to our environment.
Biofilms are communities of microorganisms that attach to each other and often to surfaces, such as the inside of pipes. Ubiquitous in aquatic environments, once established they extrude molecules that form an extracellular matrix that offers them protection and makes their removal especially difficult.
In the laboratory, biofilms are particularly bad news. They can be an ongoing source of contamination since bacteria, along with their associated endotoxins and nucleases, are released in unpredictable bursts. But on the other hand, engineers at wastewater treatment plants can make use of biofilms, integrating them into existing processes to improve capacity by as much as 200%. As a potential way of curbing their flow into the environment, researchers are now looking at whether bacterial biofilms can help remove engineered nanoparticles from wastewater.
In a new study, scientists at the University of Arkansas explore whether living biofilms of bacteria can successfully remove Ag-NPs from wastewater.1 The team made Ag-NPs in the laboratory, taking great care to avoid introducing contaminants during the synthesis process by using acid-washed glassware rinsed three times with ultrapure water from an ELGA PURELAB Flex system.
The periodic recirculation in PURELAB flex also helps to prevent biofilm from building up in water used in labs. The researchers then created artificial biofilms using different combinations of four species of bacteria typically found in wastewater. They then carried out a series of carefully controlled laboratory experiments to investigate the ability of their biofilms to accumulate Ag-NPs from synthetic wastewater.
They found that a biofilm composed of two species, A.calcoacetius and D.acidovorans, accumulated the highest concentrations of Ag-NPs. In further tests, they determined that small concentrations of Ag-NPs attach to the biofilm and are subsequently released.
Given the dynamic nature of living biofilms, the phenomena of Ag-NP accumulation within the biofilm and their subsequent release is valuable knowledge that will also help to improve understanding of biofilm-nanoparticles interactions in other systems.
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Walden, C. & Zhang, W. Bioaccumulation of silver nanoparticles in model wastewater biofilms. Environmental Science.: Water Research & Technology. 2018. DOI:10.1039/c8ew00102b
Dr Alison Halliday
After completing an undergraduate degree in Biochemistry & Genetics at Sheffield University, Alison was awarded a PhD in Human Molecular Genetics at the University of Newcastle. She carried out five years as a Senior Postdoctoral Research Fellow at UCL, investigating the genes involved in childhood obesity syndrome. Moving into science communications, she spent ten years at Cancer Research UK engaging the public about the charity’s work. She now specialises in writing about research across the life sciences, medicine and health.