Poly-aromatic hydrocarbon (PAH) inputs from the Rhône River to the Mediterranean Sea in relation with the hydrological cycle: impact of floods.

The concentrations of dissolved and particulate polycyclic aromatic hydrocarbons (PAHs) were monitored in waters of the Rhône River (France) every fortnight for a full calendar year, from June 1994 to May 1995. All flood events occurring over the course of the experiment were sampled at higher frequency to better quantify the impact of these extreme hydrological episodes on the annual export of PAHs to the Mediterranean Sea. This time-series indicates that more than 90% of the annual load of particulate PAHs is transported during flood episodes, with 77% discharged during the course of only one extreme flood event occurring in November 1994. During these intense events, riverine particles are depleted in PAHs while at low river discharge particles are PAH-enriched. Dissolved PAHs were less variable and less abundant than adsorbed PAHs, consistently with the low solubility of these compounds.