Déchets marins et microplastiques

4. Can micro-plastics transport contaminants into the marine environment?

Persistent, bioaccumulating and toxic compounds or PBTs can be transported in the atmosphere or in water. Plastics found in the ocean contains a wide-range of such organic contaminants like PCBs, chlorinated, brominated or fluorinated compounds as well as petroleum hydrocarbons. Three possible fates for the contaminants have been imagined:

Hypothesis 1; the way PBTs are attached to micro-plastics is reversible.

Micro-plastics then act as transporters of the PBTs between environments where their concentration is high to the cleaner areas contaminant concentration is lower.

Hypothesis 2; for most PBTs, atmospheric transport dominates.

Micro-plastics may matter as a source of PBT’s only where long-range atmospheric transport is low. In view of the low concentrations of micro-plastics reported in the Ocean, it seems likely that long-range atmospheric transport will dominate along wind trajectories.

Hypothesis 3; micro-plastics are stable in the surface water

Micro-plastics then serve to stabilize the PBTs and reduce either their sedimentation or their uptake in the food web.

It is suspected that plastics may transfer those PBTs that do not undergo long-range atmospheric transport from coasts to the interior of Oceans. Time-scales of uptake and release are a function of the type of plastic, its size, the compound of interest and diffusion between plastic and water.

The workshop considered that the quantification of the size ranges and identification of the type of plastic particles present in the environment needs to be given priority; this will allow a better understanding of the kinetics of plastic-absorbed contaminants as well as potential chemical and physical effects related to particle size. Furthermore, uptake and distribution patterns of micro-plastic particles along food-chains needs to be analysed in different geographic areas. More...