Erik Björn lab

Our research program is focused on the biogeochemical cycling of mercury (Hg). Mercury pollution is a major environmental issue and Hg is considered by the World Health Organization as one of ten chemicals of largest public health concern. Methylmercury (MeHg) is of particular concern for human health as it is a neurotoxin that bioaccumulates and biomagnifies in the aquatic food web, potentially causing high human exposure via fish consumption. Indeed, it is estimated that 10 percent of children born in Sweden, and in total 1.8 million children per year within the EU, have been exposed prenatal to Hg levels considered unsafe.

We study how the chemical structure (speciation) of Hg control mechanisms and kinetics for reactions which are central for the cycling of Hg in the environment. We aim to both understand such processes at the molecular level and to establish their importance in natural environmental systems. In particular, we study methylation and redox reactions and bioaccumulation processes of Hg. These processes are largely mediated by various types of microorganisms and our research is therefore largely conducted at the border between biogeochemistry and microbiology.

To achieve our research objectives, we develop analytical methods and experimental strategies to determine molecular structure of Hg compounds (including Hg bonding to microbial cell membranes), concentrations and thermodynamic stability constants of compounds and rate constants for their formation and degradation. We carry out experimental studies on both controlled model systems of varying complexity and on natural systems at realistic conditions. Principal analytical techniques and research approaches for our work include:

• Chromatography – mass spectrometry coupled techniques, in particular GC- and LC-ICPMS and LC-ESIMS/MS. These are used for selective determination of trace metal compounds at low concentrations, and often in combination with the use of isotopically enriched tracers.
  
  
• X-ray absorption spectroscopy, in particular synchrotron-based techniques, to further characterize chemical structures of trace metal compounds.
  
  
• Thermodynamic and kinetic modeling approaches, to determine chemical speciation and the rate of reactions.
  
  
• Vibration spectroscopy and microscopy techniques to characterize physiological and morphology properties of microbial cells and biofilms.
  
  
• Characterization of microbial communities and aquatic food webs in close collaborations with microbiology and ecology partners.
  
  
• Incorporation of mechanistic process understanding in regional and global scale biogeochemical and food web models for Hg in collaborations with partners.