A filter cartridge apparatus is provided for a respirator. The apparatus contains a wettable filter medium for use with a respirator in order to filter tritium, the filter medium being wetted when in use. The apparatus is also mountable to a cartridge containing a separate HEPA or other filter that is typically maintained in a dry state. Thus, a single unit containing both wet and dry filter media is provided for mounting to a respirator so that tritium or tritium water vapor and particulate contaminants can be filtered at the same time.