Spatial distribution, vertical profiles and budget of organochlorine compounds in Western Mediterranean seawater

Abstract

Individual PCB congeners (IUPAC Nos. 28, 52, 44, 70, 101, 118, 153, 138, 187, 128, 180, and 170), hexachlorocyclohexanes (HCHs) and dichlorodiphenylethanes (DDTs) were determined in 15 samples of suspended particulate matter (> 0.7 μm) (SPM) collected in the Catalan Sea and the Gulf of Lions. Furthermore, 6 vertical profiles were sampled at the Ebro and Rhoˆne River mouths, Sicilian and Gibraltar Straits, off-shore Barcelona and in the open sea. Finally, 6 dissolved phase samples from the Catalan Sea were taken and analysed. The highest PCB and DDT concentrations were detected offshore Valencia (26 and 2.8 pg l−1, respectively). Other sources of pollution were identified at the Ebro transect. Spatial variability shows an enrichment of organochlorine compounds (OCs) in a thermohaline front located midway between the Iberian Peninsula and the Balearic Islands. Vertical profiles of OCs in the SPM show for the first time, a surface enrichment pattern exhibiting concentration maxima in phyto- and zooplankton zones and declining OC concentrations with depth, except nearby sewage disposal sites offshore from Barcelona. Concentrations of PCBs (28–63 pg l−1) and DDTs (0.8–4.3 pg l−1) in the dissolved phase were one order of magnitude higher than in the corresponding particulate phase (1.7–16.6 and 0.16–0.98 pg l−1, respectively). Residence times of the SPM were estimated at every depositional area ranging from 1.46 to 8.05 years for PCBs and from 0.46 to 1.32 years for DDTs. Concurrently, sedimentation rates of SPM ranged from 0.37 to 0.78 m d−1 for PCBs and 1.18 to 4.68 m d−1 for DDTs. The PCB budget in the seawater of the western Mediterranean was computed using a three ☐ model accounting for 2.4 and 14.1 t in the particulate and dissolved phases, respectively. The DDTs budget was estimated to be ca. 179 and 717 kg in the particulate and dissolved phases respectively. Finally, the input of PCBs through the Gibraltar and the output through Sicilian Straits amounted for 1.5 and 1.3 t y−1, respectively. Concurrently the corresponding input and output for PCBs were 92 and 82 kg y−1 through Gibraltar and Sicilian Straits, respectively.