Degradation under atmospheric conditions (which is the
case for floating or even submerged plastic pieces in the
ocean), generally involves - but is not limited to - chemical
absorption of oxygen atoms in the polymer chain in the
form of ketones (C=O), hydroxyl (OH) or carboxylic (COOH)
groups. Due to this oxygen uptake, advanced degradation
leads to an increase of material density, which we indeed
observed in our samples from Hawai’i (Sub-section 9.1.3).