Sorption of trace elements (Cd, Cu, Hg, Pb, and Zn) by macro- and microplastics within intertidal sediments; A laboratory, field and modeling approach

Plastic are now the main fraction of marine and beach litter as a result of the increasing production and wide range of applications. Due to continuous degradation, long residence times, and behaviour, there is widespread concern and gaps in knowledge regarding the growing impacts of plastic macro- and microparticles on marine and freshwater ecosystems and human health. The potential threat that plastic particles impose on ecosystems varies from ingestion by a wide range of aquatic organisms to their ability to sorb a diversity of environmental pollutants including trace elements. Only a few studies have addressed trace elements-plastic particles interactions within marine intertidal sedimentary environments. To address these current knowledge gaps, I applied laboratory, field, and modelling approaches to examine the sorption of Cd, Cu, Hg, Pb, and Zn by macro- and microplastics of PETE and HDPE within marine intertidal sediments. First, I used field experiments in the intertidal area of Burrard Inlet (Canada) to compare long-term sorption of trace elements by 4 types of plastic macro- and microparticles within two contrasting intertidal sediment environments. I found that trace elements sorption by plastic macro- and microparticles are dependent of sediment geochemistry and polymer characteristics and degradation status. Sorption of trace elements by macro- and microplastics decreased with increasing organic matter concentration in sediments. Plastic particles play a minor role in trace elements sorption in the presence of organic matter at high concentrations as a result of competitive adsorption. Second, I used controlled laboratory experiments to test the dependence of temperature on trace element sorption by plastic macro- and microparticles within intertidal sediments. Temperature alters the sorption of metals by plastic by altering the rate of reaching equilibrium and equilibrium concentration. Constant temperature had only a minor influence on the partitioning of trace elements in presence of organic matter at high concentrations. Lastly, I show that PFOM and PSOM kinetic models do not perform well in testing data derived from sorption experiments and suggest a framework for the future development in modeling and predicting of trace elements sorption by plastic particles within intertidal sediments. Overall, this thesis enhances our understanding of trace elements-plastic particles interactions in intertidal sediments and provides a tool that can be used to assess the conditions under which macro- and microplastics pose the greatest threat by providing an additional vector of Cd, Cu, Hg, Pb, and Zn exposure into benthic food webs.