Investigating the properties of plastic resin pellets found in the coastal areas of Lesvos Island

Plastic pellets (small granules, 1-5 millimeters in diameter) are widely distributed in the ocean
and coastal zones all over the world. They are an industrial raw material for the plastic
industry and are unintentionally released to the environment both during manufacturing and
transport. These pellets are highly persistent and because of their hydrophobic nature they
have being identified as carriers of toxic chemicals in the marine environment. Several marine
organisms accumulate plastic particles in their stomach. A positive correlation between the
mass of ingested plastic and PCBs in fat tissues has been documented. Also, plastic pellets
are proposed as indicators of organic pollution in the sea. However, the sorption mechanisms
of organic contaminants onto plastic pellets are not yet well understood. For this reason we
collected such pellets from various beaches in Lesvos island. Since this material is highly
heterogeneous we also obtained, from plastic manufacturers, virgin pellets made from
polyethylene and polypropylene. Phenanthrene was used as the model sorbate. It is a
compound with high toxicity and abundance in the environment and relatively easy to use in
the laboratory. Also, there are many publications dealing with phenanthrene sorption onto
different materials and our results are easily compared with previous research. Batch
experiments were performed to determine the sorption kinetics of the pellets. Factors under
investigation included pellet material, degree of pellet erosion, and sorption kinetic behavior.
All of the five beaches in Lesvos island investigated had plastic pellets on the sand surface.
All of these plastic pellets were eroded and 2/3 of them had similar appearance to virgin
polyethylene pellets obtained from plastic manufacturers. Pellet color is not indicative of
erosion that will lead to varying sorption kinetic behavior. Pellet density could not be used to
identify pellets sampled from the beach. Apparent sorption coefficient increases with time for
all pellets investigated. Thus, sorption into plastic pellets is limited by diffusion in the polymer
phase. 2/3 of the plastic eroded pellets demonstrate sorption kinetics similar to virgin
polyethylene pellets after 38 days.