Using Infrared Spectroscopy Analysis of Plastic Debris to Introduce Concepts of Interaction of Electromagnetic Radiation with Matter

Harmful plastic debris found on beaches and in the oceans are not limited to drinking straws or bags. There are several synthetic organic polymers that can be used to make different kinds of plastic materials and have resulted in billions of tons of waste that can reach the aquatic biome and are harmful to freshwater and marine communities as well as humans. Small pieces, known as microplastics, are very small (<5mm) and can readily be ingested by marine organisms, causing dangerous threats to the food supply chain. Although plastic debris appears as particles of varying size, shape, color, and chemical composition, its origin or source cannot easy be identified by the naked eye. Sometimes, it is also difficult to identify whether debris is made of plastics materials. However, plastic debris sources can be revealed by applying basic concepts of the interaction of infrared radiation with matter. If a sample is irradiated with infrared light, a part of the radiation can be absorbed and provide detailed information about the structure of chemical compounds, such as the arrangement of nuclei and chemical bonds within the molecule. Chemical features of a molecule allow identification of the type of polymer that makes up a plastic material. In this paper the authors describe a multidisciplinary approach to teaching the interaction of infrared light and the vibrating process of molecules to characterize plastic pollutants. The practical classes involve both indoor and outdoor activities, divided into four steps: choice of case study site; plastic debris sampling; sample preparation and physical and chemical characterization of plastic debris (size, color, shape and polymer type); data interpretation and identification of the main plastic debris sources. The first three steps, which include outdoor activities, can also be performed by students of all ages, as well as by geography, environmental science and biology teachers who are fundamental in multidisciplinary studies. The data interpretation step that involves the polymer identification is performed at the laboratory, by using ATR-FTIR and/or optical transmittance sensor systems. Finally, the identification of the main plastic debris sources and the final conclusions are tasks that can be performed in a multidisciplinary way.