Plastics in the environment

Plastic litter persists for many years, is readily dispersed by water and wind, and has been accumulating in the sea for decades. It entangles and is eaten by a wide diversity of aquatic fauna, killing them directly, or reducing their appetite. Concerns about microplastics introducing persistent organic pollutants (POPs) into aquatic foodwebs, combined with the discovery of ‘garbage patches’ in all the main ocean gyres, has sparked renewed interest in the subject. This project aims to understand and monitor plastic pollution with a view to reducing the amount entering the environment.

Plastics are used in a plethora of applications because they are lightweight, durable, have excellent barrier properties, and are relatively cheap. These properties also make inappropriately handled waste plastics a serious environmental and economic threat. The most significant threat arises from plastic ingestion, so it is important to understand why organisms ingest plastic. During 2024, Vonica Perold completed her PhD, which compared plastics ingested by seabirds with those found in the environment, and assessed changes in ingested plastic over the last 40 years. In a similar vein, CB student Abigail Campbell was awarded her MSc for a study of the long-term changes in plastic loads in White-chinned Petrels Procellaria aequinoctialis.

Although much remains to be learned about the impacts of plastics on aquatic ecosystems, we know enough to act to limit waste plastic entering the environment. Reducing plastic pollution depends on changing human behaviour through education, policy interventions, incentives, etc. Knowing where marine plastic comes from, and how it disperses through the environment, is crucial to target mitigation measures. Fitz researchers have developed indicators for the levels of environmental plastics that assess the efficacy of measures introduced to reduce plastic leakage. We monitor plastic in the environment – through interactions with biota as well as sampling on beaches. Studies of ‘general’ marine litter, such as bottles and their lids, which could come from a variety of sources, have shown that most foreign drink bottles washing ashore are dumped illegally from ships, whereas most loose lids have drifted from distant land-based sources.

However, most litter close to urban centres in South Africa comes from local sources. A more applied project, funded through the South African Waste Research Development and Innovation Roadmap, has assessed the efficacy of devices designed to trap litter in rivers and storm drains, and used spatially explicit models to identify key sites for the installation of litter traps. This project also has a social component, trying to better understand why people litter in different communities across the Cape Flats.

Activities in 2024

• Vonica Perold completed her PhD on seabird plastic ingestion, garnering many plaudits from her examiners. Her paper on the use of Brown Skua Catharacta antarctica pellets as a way to monitor ingested plastic in South Atlantic seabirds was published in Marine Pollution Bulletin, and a second paper reporting long-term trends in four frequently-ingested species appeared in Science of the Total Environment.
• Abigail Campbell was awarded an MSc for her study of long-term changes in plastic ingestion among White-chinned Petrels since the 1980s. Towards the end of 2024, she added more data from birds killed recently on fishing gear to her data set, and has a paper ready for submission to Marine Pollution Bulletin.
• PhD student Kyle Maclean expanded his original focus from the amounts of litter intercepted in rivers and storm drains to include surveys of the amounts of street litter generated in four areas in Cape Town, across the socio-economic spectrum. During 2024 he conducted workshops to assess attitudes to litter and littering in these four communities in collaboration with Prof. Rinie Schenck, SARChi Chair in Waste and Society at UWC. Kyle’s research is funded through an NRF bursary from Prof. Cristina Trois, SARChi Chair for Climate Change and Waste Management at UKZN.
• MSc student Chukwudi Nwaigwe made steady progress in writing up his study of the amount and composition of litter contributed to beach litter loads by beach-goers. He also assessed the factors influencing surf zone litter in False Bay to assess whether there is significant export of beach litter into the sea. He will submit his dissertation in March 2025.
• Peter Ryan and Coleen Moloney spent two weeks on Inaccessible Island in September 2024, where they collected data on stranded bottles and added another year of data to the long-term study using skua pellets. The bottle findings, updating the 2018 data published in PNAS in 2019, were published in Marine Pollution Bulletin.
• Vonica Perold processed all the plastics found in skua pellets and added them to the final chapter of her PhD that determined long-term changes in the characteristics of plastics ingested by South Atlantic seabirds, and compared these data with samples collected from selected remote South African beaches since the 1980s. The paper describing her findings has been submitted to Environmental Pollution.
• The final year of intensive sampling of bottles washing ashore on Marion Island was completed in April 2024. Maëlle Connan is lead author on a paper describing their origins, which will be submitted in 2025.

Highlights

• CB MSc student Abigail Campbell has updated her project to include the birds killed in 2024. A manuscript describing her findings will be submitted in early 2025.
• Vonica Perold was awarded her PhD and will graduate in 2025. She published two papers from her thesis in 2024 and will submit her final chapter for publication in January 2025. Perhaps surprisingly, she found little change in the amounts of plastic ingested by four petrels breeding on Inaccessible Island since the 1980s. However, there has been a decrease in the proportion of industrial pellets relative to fragments of manufactured items, reflecting improved pellet handling by plastics manufacturers and converters. Among plastic fragments, there has been an increase in the proportion of polypropylene relative to polyethylene. We lack a clear explanation for this change, but it was also detected in beached plastics.
• Peter Ryan led on a paper showing how the origins of drink bottle washing ashore on Inaccessible Island in the Tristan archipelago have changed over the last 6 years, with an increase in Chinese bottles more than offsetting a decrease in those from South America. He also assisted a Spanish team that reported the origins of bottles stranded in the Galapagos Islands, published in Environmental Pollution.
• Peter co-authored a paper in Marine Pollution Bulletin with Maëlle Connan and Lorien Pichegru showing how foreign drink bottle lids indicate a different litter source than foreign drink bottles on South African beaches; whereas most bottles are made in China and are dumped illegally from ships, almost all loose lids come from Indonesia, having drifted across the Indian Ocean.
• Peter also contributed to a paper led by Sarah Key from the University of Leicester, published in Environmental Pollution showing how colorants greatly affect the rate of degradation of plastic bottles in the environment.

Key co-supporters
South African Department of Science and Innovation, through the Waste RDI Roadmap, managed by the Council for Scientific and Industrial Research (CSIR); Commonwealth Litter Programme (CLiP); United Nations Environment Programme.

Research team 2024
Team leaders and collaborators:
Emer. Prof. Peter Ryan (FIAO, UCT)
Emer. Prof. Coleen Moloney (Biological Sciences, UCT)
Dr Maëlle Connan (NMU)
Dr Lorien Pichegru (NMU)
Dr Patrick O’Farrell (FIAO, UCT)
Dr Giuseppe Suaria (CNR-ISMAR, Italy)

Students:
Vonica Perold (PhD, UCT); Kyle Maclean (PhD, UCT); Chukwudi Nwaigwe (MSc, UCT); Abigail Campbell (CB MSc, UCT).