Extraction et analyse de contaminants organiques hydrophobes (HAP et PCB) retenus par les déchets plastiques en milieu marin.

Abstract

As they are persistent and bioaccumulative, PAHs (Polycyclic Aromatic Hydrocarbons) and PCBs (Polychlorinated Biphenyls), reported to be toxic or to have a chronic effect in marine organisms, are likely to (i) disrupt the marine ecosystem balance, and (ii) be transmitted from one species to another through the food chain. In this study, the individual concentrations of PAHs and PCBs retained in plastic debris floating in marine waters were determined. Two hitherto unexplored ocean regions were examined. One is nearcoastal (Java Island, Indian Ocean) while the other is in the open sea (Gyre of the North Atlantic Ocean). Analyses revealed that all collected plastic samples contained PAHs and PCBs, which indicates the contamination of both regions. A total of 15 PAHs and 39 PCBs were detected and quantified. Some are highly toxic, such as Benzo [a] pyrene, PCB77 and PCB105 (dioxin-like PCBs, priority substances). Significant differences between the two regions samples, relating to the nature of the components and their concentrations, were revealed. Thus, the mean of the cumulative PAHs' concentrations in the Gyre Polyethylene debris reached 57.7 ng/g, while their Javanese counterparts (Polyethylene and Polypropylene) had an average content 9 times higher. Cumulative PCBs' concentrations observed in debris from the open ocean waters averaged 18.6 ng/g, while coastal debris showed an average concentration 550 times higher, raising much concern. The difference in concentrations of both PAHs and PCBs observed between coastal debris and gyre debris is interpreted by the degradation and/or release of these compounds by ocean currents, during their transport from the coasts (from where they originate), to distant waters (where they migrate). From the qualitative point of view, gyre's Polyethylene debris were chiefly characterized by heavy PAHs and low-chlorinated PCBs, whereas the coastal polyolefin debris predominantly displayed light PAHs and high-chlorinated PCBs. The pollutant distribution heterogeneity, in samples collected from the same region (Java), but at five different sampling sites, is mainly explained by the different distances separating these sites from human activities, the latter being the main expected source of contamination. Polymer size, its residence time in the marine environment and its age also affect contaminants' adsorption on this polymer. The significant qualitative and quantitative difference of contents between polyethylene samples and polyethylene terephthalate samples, both from the gyre, cannot be fully explained by the difference in the affinity of these polymers for PAHs and PCBs.