Abstract: The present invention relates to filtering units or cartridges useful for avoiding environmental pollution resulting from the decomposition of corpses in cemeteries. The units or cartridges comprise a non-porous container with an inlet for gases at one end and an outlet duct having its entrance within and proximate the opposite end. Gases entering said container through the inlet pass through at least the greater part of said container before reaching the outlet. A plurality of selective filtering zones lie within said container selectively to operate on gases passing through the filter from the inlet to the outlet. These zones, which may be separated by separators, including an inert and porous material to act both as a filter for bacteria and as a layer to retain the remaining filtering material in position, a layer of acidic material to eliminate amines, a layer of a metallic sulphate to remove compounds containing sulphur and a final layer of activated charcoal located proximate the outlet.