Long-term decline of radiocesium concentration in seafood from the Ligurian Sea (Northern Italy) after Chernobyl

The activity of 137Cs, 134Cs and 40K in tissues from fish, molluse and shellfish of the Ligurian sea was measured during 1987–1988. The mean annual concentrations in 1987 were 5.92 ± 4.1 Bq/kg (wet tissue) for 137Cs and 2.7 ± 1.5 Bq/kg for 134Cs and 2.46 ± 1.82 and 0.33 ± 0.57 Bq/kg respectively in 1988. The mean value of 40K activity was 138.6 ± 22.1 Bq/kg. Contamination was significantly higher in the littoral area up to 1000 m from the coast (8.39 ± 7.6 and 1.74 ± 2.08 Bq/kg respectively versus 2.91 ± 1.87 and 0.58 ± 0.59 Bq/kg respectively in the open sea). The common octopus (Octopus vulgaris) had the highest radioactivity values and could be utilized as an indicator of radioactivity pollution. There were no significant differences regarding the trophic level, the seafood phylum, or the east and west Ligurian sea areas. Long-term reduction in the sea habitat was estimated at about 200 days for 137Cs and 110 days for 134Cs, reflecting differences in the physical half-life of these radionuclides. These values were lower than those found in terrestrial foodstuff and could have reflected dilution of the contaminants in the open sea. The effective dose equivalent for the Ligurian population of radiocesium originating from seafood was estimated at 1.3 μSv in 1987 and 0.5 μSv in 1988. These values represent 0.8 and 0.3% respectively of the annual dose (180 μSv/year) due to 40K intake with the diet.