In an earlier study of 37 a-Si:H films we identified positive correlations between the saturated light-induced defect density Nsat, the hydrogen content CH measured by IR absorption, and the optical gap. Impurities also have been implicated in the production of metastable defects. Yet no conclusive evidence has been produced that non-dopant impurities cause defects. This situation led us to analyze our samples for impurity content. Our present 42 samples were made in six laboratories by ten combinations of deposition technique. The concentrations of H, B, C, N, O, F, Na, Cr, and Ge were determined by secondary ion mass spectroscopy. Na, Cr, or Ge were not detected. The content of C, N and O varies by a factor ∼1,000 and depends on deposition system and source gas. We report a comprehensive evaluation of our data with emphasis on their correlation with optoelectronic properties. We find the annealed state defect density Nann, and the saturated light-induced defect density Nsat surprisingly independent of impurity content.