An investigation of potentially toxic element content in beached plastic resin pellets from Kuwait and the United Kingdom

Plastic is the dominant form of debris in the marine environment, with microplastics of particular concern due to their wide distribution and impact. Microplastics contain catalyst residues and additives such as plasticisers and fillers. They can absorb hydrophobic persistent organic pollutants (POPs) from the surrounding environment. Recent evidence indicates they can also be a vector for potentially toxic elements (PTE). Plastic resin pellets were collected from the foreshore at Limekilns, Scotland, UK and from Shuwaikh Port, Kuwait. They were air-dried, sieved, rinsed with deionised water and then classified using FTIR analysis. Examples of each type of plastic pellet were subjected to a two-step extraction procedure: cold leaching for 24 h in 20% aqua regia followed by microwave-assisted digestion in nitric acid. Aluminium, As, Ca, Cd, Cr, Fe, Mn, Na, Pb, V, and Zn were measured in the extracts by ICP-MS using an Agilent 7700x instrument. Pellets collected from Limekilns were 68% polyethylene and 32% polypropylene, while samples from Kuwait were 45% polyethylene and 45% polypropylene. Analyte concentrations were higher in polyethylene than in polypropylene pellets at both locations, and concentrations of Al, As, Cr, Ni, and V are significantly higher in Kuwait than in the UK samples. Larger amounts of PTE were released in the first step of the extraction than in the second step, except for Ca, Mg and Na. The latter were also detected in virgin pellets, suggesting they were incorporated during pellet manufacture rather than sorbed from the marine environment.