Bottles and lids are a useful way to disentangle these different sources of litter. In 2020, the entire Walker Bay beach was walked to sample for bottles (27 February) and lids (17 September). These items were examined for manufacturers marks and information on the date of manufacture to infer the origins and ages of litter items. The southern 3 km was again cleaned on 18 November, roughly two-months after the International Coastal Clean-up event.
Results and Discussion
A total of 462 bottles and 2219 lids was collected (88% and 79% during initial surveys, respectively). During the November collection, a further three full garbage bags of mostly plastic litter was collected, weighing a total of some 15 kg. The surveys along the entire beach indicated that cleaning effort is concentrated at either end of the beach, where access is easiest. Future clean-up efforts should target the central part of the beach, where the standing stock of litter is appreciably higher. Litter densities tended to be greater at the southern (De Kelders) end of the beach, presumably due to the accumulation of litter there due to local physical processes. The proportion of old soft drink lids (>10 years old) was greater at the southern end of the beach than the northern end, supporting the notion that litter accumulates towards the south of the beach.
More than two-thirds of bottles could be assigned to a country or region of manufacture. Almost one third (31%) were not made in South Africa, with bottles from 21 countries other than South Africa found on the beach. Most foreign-manufactured bottles came from Asia (75%), followed by South America (11%) and Europe (7%), with only 3% each from North America and the rest of Africa. Among bottles that could be ascribed to a specific country, most came from China (30%), followed by Indonesia (16%) and Malaysia/Singapore (14%). However there was a marked difference between PET and HDPE bottles. China (44%) and Malaysia/Singapore (20%) accounted for most PET bottles, with none from Indonesia, whereas Indonesia accounted for 55% of HDPE bottles. Many of the Indonesian bottles bore bite marks typical of bottles that had been adrift at sea for an extended period. It is likely that the HDPE bottles, which remain afloat even if full of water, drift across the Indian Ocean in the South Equatorial Current, whereas most PET bottles are dumped from ships. In support of this, most of the PET bottles were manufactured too recently to have drifted from distant source countries. For example, we found a Taiwanese water bottle on 18 November 2020 that was manufactured less than 2 months earlier, on 20 September 2020.