Supervisors info:
Αριάδνη Αργυράκη, Καθηγήτρια, Τμήμα Γεωλογίας και Γεωπεριβάλλοντος, ΕΚΠΑ
Summary:
Considering the estimated maximum 300k Tn of microplastics (MPs) released yearly in the EU and the scarcity of systematic surveys for MPs, monitoring and managing their potential risks poses notable challenges to researchers and governments worldwide. Primarily owing to their small size and complex composition, the lack of standardization on methodologies for sampling & analysis, reporting units, and QA/QC procedures, present significant challenges for synthesizing research findings, interpreting data, and drawing meaningful conclusions. Furthermore, up to now the focus of research has been mostly on developing methods to estimate the amount and type of MPs in the marine environment. Standardized protocols for the recovery and characterization of MPs in soils are still under investigation, although it has been established that they are characterized by elevated adsorption capacity as the result of their large specific surface area; thus, they adsorb typical soil contaminants such as metals and metalloids, promoting their dispersion in the environment.
In this study, soil samples were selected from the systematic soil dataset of the Attica region in Greece, taken at depths of 0-20 cm and 20-40 cm. Spiking experiments were conducted using a composite mixture of soil collected at natural forest sites and blank samples spiked with cryomilled polymers. Various techniques and reagents were tested to enhance recovery and facilitate characterization. Different reagents were compared regarding their effectiveness on the degradation of organic particles, including Strand solution (0.67 mol/L NaClO, 0.45 mol/L KOH), KOH (2.6%), H2O2 (30%), and one using porcine pancreatic enzymes. Mineral particle removal involved density separation with supersaturated NaCl and ZnCl2 solutions, followed by filtration to retain MPs. Modifications were made in the choice of reagents for repeated experiments. A multi-method approach for identifying and characterizing MPs included analysis with an optical microscope, FTIR, and Raman spectroscopy for evaluating the MP recoveries based on different treatments. All pre-treatment methods effectively could reduce some organic matter aggregates and both chlorine solutions extracted lighter plastic particles such as polyethylene (PE) and polystyrene (PS). Despite their higher density, PVC PET and tire particles were obtained from both density solutions, by observing them with an optical microscope. However, the KOH and Strand solutions were unable to decompose organic aggregates. It’s important to continue the experimental procedure by counting particles using FTIR – mapping software, to apply the methods from the spiking experiment to soil samples of unknown microplastic contaminants.
Keywords:
Microplastics (MPs), Contamination, Characterization methods, Density separation
