However, a new study has found that not all mercury is equally toxic, as its chemical form makes a big difference. Researchers at the ESRF (European Synchrotron), together with CNRS, ENS Lyon and the Institute of Marine Research in Norway, have now unveiled how Atlantic bluefin tuna transforms the toxic form of mercury into less harmful forms. Using the ESRF’s intense X-ray beams, the study team tracked how mercury is processed inside Atlantic bluefin tuna. The team found that part of mercury in edible muscle of Atlantic bluefin tuna occurs as a tetraselenolate complex — Hg(Sec) 4 — which is arguably not toxic, since this complex transforms into inert mercury selenide in the spleen. The Atlantic bluefin tuna is a high trophic predator, like bigeye tuna, so the results of this research cannot be extended to lower trophic tuna species, which contain much less mercury.