Renormalon contributions to Δϱ

Leading QCD vacuum polarization contributions to the electroweak parameter Δϱ are evaluated numerically using several different prescriptions for the gluon self-energy. Simple theoretical estimates of the asymptotic behavior are given. The results show a significant contribution from the leading infrared renormalons when Δϱ is expressed in terms of the top-quark pole mass and its absence when the MS running mass is employed. The calculations are applied to estimate higher-order QCD contributions to Δϱ.