When people think about plastic in the ocean, they often imagine a long journey that sees waste drift around the globe for years before it eventually washes up somewhere far away from its origin. Selina Pfäffli’s Bachelor’s thesis paints a different picture of the Can Tho River in Vietnam. Much of the plastic identified there was neither old nor imported. Instead, it came from within the country itself and had often been produced just a few months earlier.
A barrier across the river
Pfäffli recently completed her BSc in Natural Resource Sciences at the ZHAW and carried out her thesis in collaboration with The Ocean Cleanup, a Dutch non-profit organisation that uses so-called “Interceptors” to collect plastic from rivers around the world before it reaches the oceans. For her fieldwork, she spent six weeks in Can Tho at an Interceptor installation located three kilometres upstream of the point where the Can Tho River joins the Hau River, a branch of the approximately 4,900-kilometre-long Mekong.
The installation itself is relatively unremarkable: a 100-metre-long floating barrier that covers around 17% of the river’s width and directs floating debris along with the natural current towards a conveyor belt. From there, the waste is transferred into six containers, which are lifted out and unloaded using a crane as required, a process referred to locally as “offloading.” Pfäffli observed two such operations on 7 October and 1 November 2024. In total, the Interceptor removed 1,592 kilograms of material from the water over this period.
Selina Pfäffli
Graduate of the BSc in Natural Resource Sciences, ZHAW School of Life Sciences and Facility Management
“In the future, I hope that I can continue to be involved in such exciting and relevant environmental projects and perhaps help to make the world a little bit better.”
From container to analysis tray
On a tarpaulin spread out along the riverbank, Pfäffli sorted the collected material according to an internationally standardised protocol and analysed it in detail: origin, brand, production and expiry dates, degree of degradation and type of plastic. In this way, she examined 342 clearly human-made objects individually.
Describing her fieldwork, Pfälli explains that a typical day began with an offloading operation, i.e. the emptying of the containers. She would then sort through the contents, select representative items, allow them to dry, and finally measure, photograph and document each object individually.
Fresh, local and impossible to ignore
The majority of the material intercepted (92 % by weight) was organic in nature, primarily floating water hyacinths, which the Interceptor is unable to distinguish from actual waste. Within the remaining plastic, however, a clear pattern emerged: of the items whose origin could be determined, 85.7 % were produced in Vietnam by local companies under domestic brands. More than three-quarters of the objects that could be dated had been produced within the previous year.
The origin was most frequently identified in the case of PET drinking bottles. At 52 items, they constituted the largest single category, followed by plastic bags and polystyrene fragments. Takeaway packaging from restaurants and the nearby night market featured prominently among the objects found. For Pfäffli, this suggests that a large proportion of the waste is not imported, but rather is generated and discarded directly along the river.
Where the data reaches its limits
The picture is not entirely complete, however. For around two-thirds of the 342 items examined, it was not possible to identify either the brand or the country of manufacture with certainty – labels had faded, were missing or could not be identified due to language barriers encountered on site.
The fieldwork itself also faced limitations: delays in coordination between the Interceptor operations, transport vessels and waste disposal companies extended the offloading intervals. In addition, the reference samples used for the degradation analysis were drawn from the smaller sample of 342 items rather than from all 1,744 recorded pieces. In her thesis, Pfäffli openly acknowledges these limitations, not least because they demonstrate just how much manual work and discretion are still required – even in the case of a standardised field protocol.
The people behind the project
Pfäffli first came into contact with The Ocean Cleanup through a lecture in her first year of study, which sparked her enthusiasm for the subject. During a semester abroad in the Netherlands, where the organisation is based, she sought direct contact. What began as a visit developed into a collaboration, and this collaboration ultimately became a Bachelor’s thesis conducted on the other side of the world.
On site, Pfäffli relied on an experienced team. Nadhira Putri organised the logistics of the fieldwork, while Thanh Do, Operations Manager in Can Tho, was responsible for coordinating with Interceptor operations, transport vessels and the waste disposal companies. The project was also made possible through the Sustainable Impact Program at the ZHAW, which provides financial support for projects such as this one.
Adapted from the following sources:
