Occasionally, a situation arises – often the result of unforeseen consequences of man’s activity – that poses a new and significant challenge to the natural world and, ultimately, human health. In recent years, images of plastic pollution in the environment have become commonplace – particularly in the seas and oceans of the world. For an up-to-date overview, visit Coastal Care: a nonprofit foundation dedicated to defending the beaches and shorelines of our shared planet, and read our blog: The plastic in our food chain.
Importantly, the ‘large-scale’ pollution caused by discarded plastic goods is accompanied by micropollution. That is, the formation of microscopic particles of plastic (from 1 to 5 mm in size and known as microplastics) that are thought to be potentially much more damaging to the natural world.
• Persistent in the environment, many common compounds are nonbiodegradable
• Surface chemistry changes that occur in seas and oceans can make microplastics appear as food – leading to accumulation throughout the marine food chain
• Airborne microplastics can be inhaled into lungs, where they may lodge or act as a vector to transport other chemicals into the body
• Plastic packaging can contaminate food and water, bringing microplastics into the human body
• Scientific knowledge and understanding of the impact of microplastics remains limited – making it difficult to set appropriate limits and regulations
One early consequence of such issues is the need for specific, sensitive, and robust analytical approaches that allow the identification, quantitation, and monitoring of the situation. For an analytical method to gain universal acceptance, availability of analytical instruments, simple sample preparation routines, and straightforward experimental protocols are also essential.
A range of techniques, including all forms of gas and liquid chromatography, ICP-MS, and Fourier transform infrared (FTIR) spectroscopy make up the analytical toolbox of a typical environmental chemist. Researchers across the world are now working towards standardized analytical methods to best characterize microplastics in terms of chemical identity, particle size and shape, and total mass.
Professor Jes Vollersten and his team at Aalborg University in Denmark are leading this initiative, developing robust sample preparation methods and innovative data analysis tools. The goal is to achieve a level of standardization across the analytical routine. It will enable scientists around the world to compare results with confidence as they assess the true impact of microplastics in the environment.
For microplastic particles down to around 10 μm in size, the group is using laboratory-based FTIR imaging as their preferred analytical solution. The system comprises of an Agilent Cary 620 FTIR microscope coupled to an Agilent Cary 670 FTIR spectrometer. In addition, rapid field-based characterization and chemical identification of microplastic particles greater than 5 mm is being developed using mobile FTIR analysis.
Environmental samples are complex. The multicomponent matrix of organic and inorganic elements creates well-known challenges for analysts everywhere. The approach taken by Professor Vollersten’s team has been shown to provide a reproducible and representative sample for FTIR imaging from raw samples of water, sediment, and fish.
Oxidation by H2O2 was used as the main pretreatment step, as it would preserve the plastic while removing unwanted organic material. Water samples were concentrated by sieving and flushing with ethanol; sediment samples were sieved, freeze dried and gravimetrically weighed. Separation was used to split the organic/inorganic phases; fish samples were freeze dried, resuspended, and sieved.
The final concentrated plastic particle samples from each of the three sample types were suspended in ethanol and prepared for FTIR imaging on the Agilent system in either reflection or transmission mode.
Spectra were analyzed using MPhunter, a freeware software package developed at Aalborg University, Denmark, in collaboration with the Alfred Wegener Institute in Germany.
Professor Vollersten’s analytical approach proved a rapid and accurate way to automatically identify and quantify microplastics and other materials. The authors concluded that: “Combined with H2O2 oxidation, FTIR imaging is a strong candidate to be a standard method in microplastic analysis.”
A recent webinar: ‘Microplastics, from Beach to Bench: Complete Characterization and Chemical Identification Using Mobile FTIR and FTIR Imaging Technologies.’ is now available ‘on-demand’ – access and view it here.
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Keywords: microplastics; FTIR imaging; environmental pollution