A new modelling study shows that the Seychelles and other islands in the western Indian Ocean are not responsible for most of the plastic waste that accumulates on their beaches.
Indonesia, India and Sri Lanka were found to be the main sources of land-based plastic debris.
The Seychelles also accumulate significant amounts of plastic debris of marine origin from fisheries and shipping lanes.
A Global Plastics Treaty
The results highlight the urgent need for a legally binding Global Plastics Treaty and greater enforcement of regional policies to reduce plastic waste.
Vast amounts of plastic debris accumulate on beaches across the Seychelles and other small island developing states.
Observational analysis – of plastic bottle labels, for example – suggest that much of this waste originates from distant sources and not from the islands themselves. But until now, the likely sources of this debris have not been quantified.
Plastics in the sea
A new study led by the University of Oxford investigated this by developing a high-resolution model that simulated the movement of plastic debris across the world’s oceans.
It used input data on ocean currents, waves and winds, and plastic debris entering the ocean from coastal populations, rivers and fisheries, to predict plastic debris accumulation at 27 sites in the Seychelles and wider western Indian ocean.
The researchers modelled the likely sources of both land-based and marine types of plastic pollution, and the results have been published in Marine Pollution Bulletin.
Sources of plastic debris
According to the research, Indonesia is the primary source of land-based plastic debris found on beaches in the Seychelles, with major contributions from India and Sri Lanka.
This was particularly the case for medium and large debris with a high buoyancy, such as bottle caps, sandals, bottles and small domestic items.
Plastic debris arriving from Indonesia would have been at sea for at least six months, and some for more than two years.
Smaller plastic debris, such as millimetre-sized plastic fragments and pellets, tended to originate from East Africa and from within the Seychelles itself.
Smaller fragments are less buoyant than larger items, and do not travel as far before sinking.
The Seychelles also accumulate significant amounts of plastic debris of marine origin from fisheries and shipping lanes, such as discarded or lost fishing gear.
The large numbers of bottles beaching at these islands with labels suggesting they come from Malaysia, Thailand and, in particular, China, were probably discarded from ships rather than floating from those countries directly.
For some islands, a significantly higher proportion of plastic waste comes from marine sources rather than land.
Seasons and plastic pollution
Rates of plastic debris accumulation showed a strong seasonal effect.
Plastic debris from both land and marine sources was most likely to land on beaches in the Seychelles at the end of the northwest monsoon, with the highest rates in March and April.
Plastic debris accumulation may also be amplified by El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD, also known as the Indian Niño) events.