A more recent study by Laurent Lebreton and colleagues suggests that 96%-98% of litter from land-based sources washes up within one year of entering the sea.

Olivelli's survey of beaches around Australia found that most litter items were concentrated on the backshore storm strand line, where litter items were larger on average than along recent tide-lines closer to the sea.

South Africa is an ideal place to study the fate of marine plastics because it is far from other major litter sources, and so most of the litter comes from local sources.

Jambeck's 2015 study estimated that the high proportion of mismanaged waste in South Africa results in 90,000 tonnes to 250,000 tonnes of plastic entering the sea each year.

To directly measure the amount of plastic leaking into the sea from urban areas, my student Eleanor Weideman sampled litter loads in Cape Town storm drains.