Forms of mercury in the Baltic mussel (Mytilus trossulus): Human and ecosystem health risk assessment.

Mercury (Hg) is one of the most dangerous environmental pollutants. A significant source of this toxic element to the human body is the consumption of seafood - including the increasingly popular mussels. Mussels also play an important role in the marine ecosystem, providing a food base for fish and birds. The study aimed to determine the level of total Hg and its labile and stable forms in the Baltic mussel (Mytilus trossulus), as well as to indicate the factors that shape them. The research was conducted in the Puck Bay (Polish part of the southern Baltic Sea) in 2012-2013. The study material consisted of M. trossulus mussels, the components of their diet (suspended matter and phytoplankton), and surface sediments. Concentrations of total Hg (HgTOT) and the individual Hg forms were established using the thermodesorption method on a DMA-80 analyser (Milestone). The obtained results showed that the level of Hg concentration in M. trossulus from the Puck Bay was shaped by the individual features of specimens, related to the growth and reproductive cycle of mussels, as well as the quality of food consumed by them. The total share of labile Hg forms in M. trossulus was high, exceeding 90% of HgTOT, and the predominant form was the most dangerous organic Hg. This means that almost all of the Hg accumulated in mussels can be transferred to higher trophic levels. The obtained results showed that Baltic mussels were characterised by levels of HgTOT and organic Hg deemed to be safe for humans. A positive relationship was noted between the HgTOT concentration in a mussel's tissues and the length of its shell. Smaller sized organisms demonstrated not only by lower Hg concentrations, but also by better condition and, consequently, higher nutritional value.