By utilizing multifrequency electron paramagnetic resonance (EPR) spectroscopy, the iron functional center in Fe3+-modified polycrystalline lead zirconate (PbZrO3) was studied. The single phase polycrystalline sample remained orthorhombic and antiferroelectric down to 20 K as confirmed by high-resolution synchrotron powder diffraction. The Fe3+ ions were identified as substituting for Zr4+ at the B-site of the perovskite ABO(3) lattice. Similarly as found for Fe3+:PbTiO3 [Mestric , Phys. Rev. B 71, 134109 (2005)], the value of the fine-structure (FS) parameter B-2(0) is only consistent with a model in which a charged (Fe-Zr(')-V-O(center dot center dot))(center dot) defect associate is formed. In contrast to a well defined iron functional center in lead titanate (PbTiO3) with FS parameters exhibiting variances of less than 3%, a strong broadening of the EPR powder pattern was observed in lead zirconate, indicating a much larger variance of FS parameters. It is suggested that the apparent broad distribution of fine-structure parameters arises from the system's capability to realize different oxygen vacancy positions in the first coordination shell around the iron site. This proposed model of a small number of distinct iron-oxygen vacancy sites is supported by the observation that corresponding B-2(0) and orthorhombic B-2(2) FS parameters of these sites are anticorrelated, a property not expected for random distributions of fine-structure parameters.