Mikael Kaandorp and colleagues at Utrecht University built a model that combined measurements of plastic on beaches, at the surface and in deep water with data on fragmentation and sinking, to reconcile the long-standing puzzle of why far less plastic is found at sea than was thought to enter it.
They estimated about 3.2 million tonnes of buoyant plastic in the ocean in 2020, with an annual input of about 0.5 million tonnes, far below earlier estimates of 1–4 million tonnes and more. Between 90% and 98% of the mass is in items larger than 25 mm.
The key insight is that ocean plastic persists. Most of it is large, long-lived items that stay at sea longer than earlier models assumed, and the model suggests the amount at sea is still increasing.
This figure covers only buoyant plastic and is not comparable with Borrelle 2020 (all aquatic environments) or Jambeck 2015. Do not mix them in the same sentence.