Pollution historical trends as recorded by sediments at selected sites of the Venice Lagoon

Polychlorinated biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), dibezofurans (PCDFs) and hexaclorobenzene (HCB) were determined in three sediment cores of the Venice Lagoon: I1, from the San Giuliano Canal that is likely the main source of pollutants for the study area; E, representing the lagoon sediment of the zone of Campalto; and M3, typical of a salt marsh environment and mostly subject to atmospheric inputs. Maximum concentrations were found in core I1: 25-1858 ngl-TE kg-1 (kg to the minus 1)(PCDD/fs), 1.7-13 micrograms kg-1 (kg to the minus 1)(HCB), and 107 - 717 micrograms kg-1 (kg to the minus 1) (PCBs) are surficial and peak values, respectively. The lagoon sediment (E), is much less contaminated: 24-47 ngl-TE kg-1 (kg to the minus 1) for PCDD/Fs, 2.3-3.6 micrograms kg-1 (kg to the minus 1) for HCB, and 56-203 micrograms kg-1 (kg to the minus 1) for PCBs whereas M3 shows the lowest values: 1.6-6.0 ngl-TE kg-1 (kg to the minus 1)for PCDDs/Fs, 0.3-0.6 micrograms kg-1(kg to the minus 1)for HCB, and 7.1-39 micrograms kg-1 (kg to the minus 1) for PCBs. In any case, the recent trend is toward a decrease of pollutant concentration. The chronology of cores E and M3 is based on both Pb-210 and Cs-137 activity depth profiles. The maximum concnetrations of PCDD/Fs, HCB, and PCBs correspond to the years 1949, 1980, and 1968, respectively. The homologue profiles of PCDD/Fs confirm that I1 has been subject to an industrial source while the other sites also recorded significant contributions, changing over time, of octa-chlorinated dioxin from combustion. a comparison of the pollutatn invetories, all normalised to PB-210 invetories, suggests that the atmospheric contribution to the contamination of the area of Campalto is low: the upper limits range from 6% (PCDD/Fs) to 17% (HCB).