The Mediterranean and Black Seas are unique marine environments subject to important anthropogenic pressures due to riverine and atmospheric inputs of organic pollutants. Here, we report the results obtained during two east-west sampling cruises in June 2006 and May 2007 from Barcelona to Istanbul and Alexandria, respectively, where water and plankton samples were collected simultaneously. Both matrixes were analyzed for hexaclorochyclohexanes (HCHs), hexachlorobenzene (HCB), and 41 polychlorinated biphenyl (PCB) congeners. The comparison of the measured HCB and HCHs concentrations with previously reported dissolved phase concentrations suggests a temporal decline in their concentrations since the 1990s. On the contrary, PCB seawater concentrations did not exhibit such a decline, but show a significant spatial variability in dissolved concentrations with lower levels in the open Western and South Eastern Mediterranean, and higher concentrations in the Black, Marmara, and Aegean Seas and Sicilian Strait. PCB and OCPs (organochlorine pesticides) concentrations in plankton were higher at lower plankton biomass, but the intensity of this trend depended on the compound hydrophobicity (K(OW)). For the more persistent PCBs and HCB, the observed dependence of POP concentrations in plankton versus biomass can be explained by interactions between air-water exchange, particle settling, and/or bioaccumulation processes, whereas degradation processes occurring in the photic zone drive the trends shown by the more labile HCHs. The results presented here provide clear evidence of the important physical and biogeochemical controls on POP occurrence in the marine environment.

[1] The Mediterranean and Black Seas are unique marine environments subject to important anthropogenic pressures due to atmospheric and riverine inputs of organic pollutants. They include regions of different physical and trophic characteristics, which allow the studying of the controls on pollutant occurrence and fate under different conditions in terms of particles, plankton biomass, interactions with the atmosphere, biodegradation, and their dependence on the pollutant physical chemical properties. Polycyclic Aromatic Hydrocarbons (PAHs) have been measured in samples of seawater (dissolved and particulate phases) and plankton during two east-west sampling cruises in June 2006 and May 2007. The concentrations of dissolved PAHs were higher in the south-western Black Sea and Eastern Mediterranean than in the Western Mediterranean, reflecting different pollutant loads, trophic conditions and cycling. Particle and plankton phase PAH concentrations were higher when lower concentrations of suspended particles and biomass occurred, with apparent differences due to the PAH physical chemical properties. The surface PAH particle phase concentrations decreased when the total suspended particles (TSP) increased for the higher molecular weight (MW) compounds, consistent with controls due to particle settling depletion of water column compounds and dilution. Conversely, PAH concentrations in plankton decreased at higher biomass only for the low MW PAHs, suggesting that biodegradative processes in the water column are a major driver of their occurrence in the photic zone. The results presented here are the most extensive data set available for the Mediterranean Sea and provide clear evidence of the important physical and biological controls on PAH occurrence and cycling in oceanic regions.

We present here the first estimates of floating macro-litter in surface waters from the Rhone River, based on monthly visual observations during 1-year period (2016-2017). Plastic represented 77% of the identified items, confirming its predominance in riverine floating litter. Fragments (2.5-50 cm) and Single Use Plastics (i.e. bags, bottles and cover/packaging) were among the most abundant items. Frequent non-plastic floating litter were paper items such as packaging material and newspapers, and metal items (mostly cans), representing 14% and 5% of total litter, respectively. A lower-end estimate resulted in ∼223,000 plastic items (∼0.7 t of plastic) transported annually by the Rhone surface waters to the Gulf of Lion (NW Mediterranean Sea). Floating macroplastics are only a fraction of the total plastic export by the Rhone. Our study highlights the current discrepancy between field observations and theoretical estimations. Improvements are needed to harmonize data collection methodologies for field studies and model validation.