In an ongoing study, a Finnish research team has tested a new method for detecting and tracking the degradation of plastics in bodies of water. The team used so-called recombinant bacterial whole-cell biosensors – in short, biosensors – which were structured in such a way that they light up on contact with the monomer acrylic acid. According to the Finnish research team, the results show that the degradation of plastic waste in freshwater and salt water could be monitored with the help of these biosensors.
Microplastic is formed, for example, through UV radiation, salt and the waves of the sea during the degradation of large, improperly discarded plastic components. According to the Finnish research team, this can be proven nowadays in water specimens up to a size of one micrometre, for example through complex imaging processes such as micro-infrared spectroscopy. To identify even smaller plastic particles in the water, two research scientists from the University of Tampere, Emmi Puhakka and Ville Santala, have now applied a new method in their latest study: They used recombinant bacterial whole-cell biosensors to detect monomers in water specimens. Biosensors are usually used, for example, for the accurate in-situ and real-time detection in the analysis of water and effluent, e.g. for checking drinking water for the presence of pollutants and toxins. Sensors are described as recombinant when they are synthetically produced with the help of genetically modified microorganisms or in cell cultures. The biosensors used for the present study were used, according to the authors, for the first time for measuring plastic particles. The research team produced a bioluminescence biosensor based on the bacterium Escherichia coli (E. coli) and the firefly enzyme luciferase. The idea was that this sensor would light up when it came into contact with acrylic acid – a monomer and starting material for many plastics. Acrylic acid is formed, for example, during the decomposition of polyacrylic acid (PAA). This is utilised by the chemical industry predominantly as a starting material for the production of polymer plastics such as polyacrylates. PAA is, however, also used as a component of adhesives, polishes, paints and surface coatings.
In their study, the research scientists tested, with their developed biosensor, sterile water specimens and specimens from a freshwater lake in western Finland that had been mixed with acrylic acid in different concentrations. Apart from that, they had saltwater specimens, mixed either with PAA or polymethylmethacrylate (PMMA). The addition of PMMA served to prove that the biosensor reacts exclusively to PAA and not to other similar chemical compounds. The biosensor cells are added for sixty minutes to each specimen and then the luminescence is measured, which serves as proof of acrylic acid monomers. According to the study, acrylic acid molecules were detected with the biosensor cells in all three specimen types. Also in the saltwater specimens, the biosensor cells were able to identify the acrylic monomers stemming from PAA. According to the authors, the results show that this approach for the screening of environmental samples on plastics is suitable for both fresh and saltwater. It means, say the authors, that bacteria and enzyme-based biosensors could supplement present-day research methods for monitoring plastic monomers in water environments. In addition to this, the technology could be further developed and extended to other monomers.