Biogeochemical and physical controls on concentrations of polycyclic aromatic hydrocarbons in water and plankton of the Mediterranean and Black Seas
Résumé
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.