Metals associated with beach plastic litter at Woodbridge Island and Derdesteen in Table Bay, South Africa

Abstract

Plastics and associated metallic contaminants pose a significant ecological risk to marine ecosystems and human health. To evaluate the potential threat of plastic waste in the marine environment, the distribution of plastic litter and their associated metals at Woodbridge Island and Derdesteen Beaches, located in Table Bay, Cape Town, was investigated. Beach litter was collected over a 100-m stretch of the beaches during low tide. Plastic debris was the most dominant litter type, accounting for 88% of the 4583 litter items collected at Woodbridge Island and 78% of 713 items at Derdesteen Beaches by count. Overall, this represents a significant portion of the 5296 litter items collected. Plastic fragments were the predominant category of plastics identified. Using a Spectrum Two Universal Attenuated Total Reflectance Infrared (UATR-IR) spectrometer, 11 polymers were identified in plastic items ≤ 200 mm, with polypropylene (40%) and polyethylene (24%) being the dominant polymer categories. Of the plastic debris (≤ 200 mm) processed for metal content using an inductively coupled plasma mass spectrometer (ICP-MS), polystyrene plastics were found to contain a higher abundance of the analyzed metals. Overall, metals were detected in plastic items at frequencies ranging from 49% (Se and Cd) to 100% (Cr and Ni), with median concentrations between 0.04 mg/kg (Co) and 147.36 mg/kg (Al). Pb exhibited the highest overall median concentration (6.05 mg/kg) with a detection frequency of 53% of the non-essential metals. This study highlights plastics as a potential vector for toxic metals in the marine environment, posing a significant threat to the proper functioning of marine ecosystems and underscoring the urgent need for continuous monitoring, control, and abatement of plastic waste in marine environments.