Assessing the Ability of Marine Plastic Waste to Adsorb Heavy Metals and Emerging Organic Contaminants from Water

Student thesis: Doctoral ThesisDoctor of Philosophy (awarded by UHI)


Plastic waste has been identified as an increasing threat to the marine ecosystem. One of the most concerning aspects of plastics in the marine environment is their ability to bind contaminants and act as vector for their long-range transport. This may include established and emerging contaminants such as pharmaceuticals, radionuclides, flame retardants, industrial chemicals, etc. Meanwhile, these same contaminants present challenges in the treatment of drinking and waste waters. This project sought to couple these two issues and evaluate the adsorption capacity of ‘raw’ and ‘functionalised’ marine plastic waste as a low-cost novel adsorbent for the removal of contaminants from aqueous media.
Four different reagents were applied to functionalise polypropylene (PP) plastic ropes collected from beaches around Northern Scotland coasts, with dopamine selected as being the most effective. Scanning electron microscopy (SEM) with energy dispersive X-Ray analysis (EDX), Fourier-transform infrared spectroscopy (FTIR), and X-ray diffraction (XRD) techniques were used to examine the materials and revealed the formation of polydopamine on their surfaces.
Through a prioritisation process, which considered occurrence of environment, application, environmental and health impacts, etc., Cu2+ and Pb2+ were selected as target inorganic contaminants, while PeCB and BDE 47 were selected as target organic pollutants for evaluation. Dopamine modification was found to significantly improve the adsorption capacity for Cu2+ and Pb2+, which could achieve 317 and 536 μg/g at 40 °C, respectively. FTIR and X-ray photoelectron spectroscopy (XPS) results indicated the main mechanisms in removal to be electrostatic interaction and chelation. For the organic pollutants, dopamine modification improved the adsorption capacity for BDE 47, but decreased that for PeCB. FTIR and XPS analysis indicated the main mechanism for PeCB adsorption was hydrophobic interaction while for BDE 47 hydrophobic interaction, hydrogen bonding, and π–π interaction were involved. Modelling studies showed adsorption of both heavy metals and organic pollutants were best described by Langmuir isotherm and pseudo 2nd order kinetics models.
Column studies on Cu2+ and Pb2+ revealed that use with plastic adsorbents with activated carbon could enhance the lifetime of the latter by about 82%. The production cost of plastic adsorbents was estimated and the reduced operating costs of adding an extra plastic adsorbent column into the existing activated carbon column wastewater system were also estimated.
This study was the first to explore and evaluate the potential of marine plastic waste as an adsorbent and results suggest that these materials could be combined with other materials in wastewater treatment systems. The same results re-emphasise the potential of marine plastic wastes to bind and promote transportation of contaminants in the marine environment.
Date of Award29 Nov 2022
Original languageEnglish
Awarding Institution
  • University of the Highlands and Islands
SupervisorSzabolcs Pap (Supervisor) & Stuart Gibb (Supervisor)

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