Concentrations of Hg in Swedish marine systems are generally lower than in fresh water

systems, but still often exceed environmental target levels. As top predators in many

marine food webs, seals are exposed to heavy metals, like Hg and Cd, which are known

to biomagnify with increasing trophic level in the food web. Therefore, studies of Hg

concentrations over time are preferably conducted in relation to seal diet during the

same period. By analysis of naturally occurring stable nitrogen and carbon isotopes it is

possible to determine on which trophic level a certain organism is located and where it

feeds. The aim of the present study was to try to establish background concentrations of

Hg and some other metals in Swedish marine waters by analyses of seal bones from the

1840s and forward. Stable isotopes were analyzed in order to discover possible

correlations between metal concentrations and trophic level, and changes over time in

dietary intake of metals.

No significant change in metal concentrations was seen over time, except for a

significant decrease in Zn concentrations in Baltic Grey seal. A significant difference in

δ

15N and δ13C values between species and between Baltic and Skagerrak areas was

discovered. No significant correlation between δ

15N or δ13C values and metals was

found, however, the seal with the highest δ

15N value (Harbor seal) also had the highest

Hg concentration. Even though the δ

15N values suggested an increase over time the

increase was not statistically significant. No statistically significant change over time was

found in δ

13C values.

It is important to keep in mind that this study was based on 44 individual seals spread

over 126 years. Data on sex and age was lacking for almost half of the seals, which made

statistical analysis on these parameters difficult to perform. Even though no obvious

trends or differences in metal concentrations between areas and species were seen, the

results from this study can serve as a base for further studies and provide valuable

information for interpreting the actual contamination load in Swedish marine systems.