2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/179596We show that higher-order vacuum polarization would contribute a measureable net charge to atoms, if the charges of electrons and positrons do not balance precisely. We obtain the limit $|Q_e+Q_{\bar e}| < 10^{-18} e$ for the sum of the charges of electron and positron. This also constitutes a new bound on certain violations of PCT invariance.9 pages, 1 figure attached as PostScript file, DUKE-TH-92-38. Revised versionHigh Energy Physics - Phenomenologytext