A sealing apparatus for mitigating emissions of a hazardous gas flowing between first and second regions. A body of the apparatus includes at least one inlet, at least one outlet spaced apart from the at least one inlet, and a channel connecting the at least one inlet and the at least one outlet in fluid communication. Treatment material housed in at least a portion of the channel is adapted to treat the hazardous gas to form a conditioned gas. In use, the hazardous gas being emitted from the first region is received at the at least one inlet, and the conditioned gas is discharged to the second region at the at least one outlet. The apparatus may be used in combination with a storage container housing radioactive or other toxic waste.