QED corrections to the binding energy of the eka-radon $\mathrm{}(Z=118\mathrm{})\mathrm{}$ negative ion

Quantum electrodynamic (QED) electron self-energy and vacuum polarization corrections to the binding energy of the $8s$ electron in the eka-radon $\mathrm{}(Z=118\mathrm{})\mathrm{}$ negative ion are calculated. This ion was found recently to be stable in the Dirac-Coulomb-Breit Hamiltonian; an improved basis and correlating all 119 electrons give a binding energy of $-0.064\left(2\right)\mathrm{}\mathrm{eV}.$ The QED contribution is 0.0059(5) eV, amounting to a 9% reduction of the binding energy. This is the largest relative QED effect reported for neutral or weakly ionized atoms, and confirms the importance of QED corrections for superheavy elements.