The certified materials were bought from NIST.

Reference materials were analyzed in the laboratory for THg isotopic composition. All the samples were combusted with the marine particles and zooplankton to act as procedural reference.

For THg isotope determination the reference were combusted in a two-stage combustion furnace and Hg(0) g was trapped in a 1% KMnO4 solution. The 1% KMnO4 solution was analyzed for Hg stable isotope composition using a multiple collector inductively coupled plasma mass spectrometer.

All the methods are detailed in Motta et al., (2019).