Investigation of sorption of environmental pollutants to virgin and aged microplastics

Plastics are a diverse group of materials used in packaging, construction, medical applications, and many more. Due to their favourable properties their production and consequently their input into natural systems has increased drastically over the last decades. In the environment (photo-)oxidation processes and mechanical abrasion may then lead to the decomposition of the plastics. During this process microplastics (<5 mm) are formed. It has been noted that xenobiotics which are present in the same compartments can sorb to microplastics. However, knowledge on this topic is still limited. The work presented here aimed to investigate the sorption of the type 2 diabetes drug metformin and the triazole fungicide difenoconazole to virgin polyamide (PA), polypropylene (PP), and polystyrene (PS). Additionally, sorption to cryo-milled PP and acid-treated PA was studied. The latter was also characterised by Fourier transform infrared spectroscopy (FTIR), gel permeation chromatography (GPC), and dynamic scanning calorimetry (DSC). Sorption experiments were planned on the basis of a full factorial design with agitation, salinity, and pH value as parameters. Results of the study revealed that metformin did not show any affinity towards the tested materials. Difenoconazole however, sorbed to all microplastics. Data analysis showed that agitation is the main influencing factor, whereas salinity and the pH value held little to no significance. Mechanical and chemical treatment of the polymers led to enhanced sorption of difenoconazole. Long-term sorption experiments confirmed the hypothesis that particle size strongly influences the time until sorption-desorption equilibrium is reached.