Formation and spread of methylmercury – the weak link in risk assessment of mercury contaminated sediments

Project description

Mercury constitutes a severe threat to ecosystem viability and human health, mainly through the formation and spread of neurotoxic methylmercury (MeHg) in aquatic ecosystems. Therefore, MeHg is a critical “risk-determining” component in contaminated sediment. Current risk assessments are inadequate since they are based on measured concentrations only and do not include the potential for MeHg formation and spread.

Recent advances in process understanding of MeHg formation and the development of new state-of-the art technologies in synchrotron radiation sources and mass spectrometry now enable the transformative research required to implement MeHg formation and spread in refined risk assessments. In this project we:

1. determine the chemical forms of inorganic Hg, Hg(II), and the composition of natural organic matter (NOM) in contaminated sediment. These are the two principal controlling factors for MeHg formation;
   
   
2. identify at which conditions MeHg formation is limited by either of these factors or a combination of both. This will allow to assess if the risk for MeHg formation is controlled by an inherent property of the contaminated sediment itself (Hg(II) speciation), or determined by the biogeochemistry of the surrounding environment (NOM inputs);
    
3. evaluate and optimize the use of stable Hg isotope measurements to trace the spread of Hg(II) and MeHg from contaminated sediment to surrounding water mass, sediment and biota.

This emerging technology is the most potent for reliable source tracing of Hg and MeHg in the environment. Overall, the project deliverables are important for refining risk assessment of Hg contaminated sediment, including to predict the potential impact of environmental change scenarios and tailor land use and aquatic resource management nearby the site, as well as for optimizing mitigation measures.