Mercury and selenium in arctic and coastal seals off the coast of Norway

Abstract

Mercury and selenium concentrations (wet weight) have been determined in samples of liver, kidney and brain of grey seal ( Halichoerus grypus), harbour seal ( Phoca vitulina), harp seal ( Phoca groenlandica) and ringed seal ( Phoca hispida) caught along the Norwegian coast, 114 individuals in all. Significant differences have been found in mercury contamination between the 4 species caught in the same coastal area, Jarfjord, located at the north-east of the Norwegian coast close to the Russian border. Very low hepatic mercury levels were found in the arctic species, ringed and harp seals, ranging from 0·20 to 0·67 and 0·04 to 1·0 μg g −1, respectively, while in the coastal seal species the concentrations were 10 to 40 times higher. The corresponding ranges were 0·7 to 48·3 μg g −1 in grey seals and 0·2 to 19·0 μg g −1 in harbour seals. The median values were 13·5 and 0·7 μg g −1, respectively. The highest levels were found in grey seals, indicating that particularly the stock frequenting the waters of the north-east coast of Norway and north-west coast of Russia had received a substantial mercury exposure. Fifty-five percent of these grey seals from Jarfjord had hepatic mercury levels above 10 μg g −1 and 21% had levels above 20 μg g −1. By a one-way analysis of covariance, sex and age were found to explain 28 and 30%, respectively, of the total variability in the mercury concentration in grey seal from Jarfjord. Significant differences in mercury concentrations were also found between stocks of harbour seals caught at different sites along the Norwegian coast, and decreasing concentration from the south to the north-east coast of Norway was revealed. The renal mercury levels in the arctic seals ranged from 0·08 to 0·45 μg g −1, and about five times higher levels were found in grey seals and harbour seals. The mercury levels in the brain ranged from the detection level (0·01 μg g −1) to about 0·1 μg g −1. The hepatic selenium levels in the arctic seal species ranged from 0·8 to 3·7 μg g −1. The corresponding ranges in grey seals and harbour seals were 1·0 to 23·3 μg g −1. The renal selenium levels were lower, and the levels in the brain were below the detection level (0·01 μg g −1). The mercury/selenium ratio was close to unity for mercury concentrations greater than 15 μg g −1, and a nonlinear, concave relationship was found between the ratio of the hepatic mol concentrations of mercury and selenium and the hepatic mol concentrations of mercury.