Scented Refresher Tabs: Dependable, safe and economical long term odour control for toilets. Chemitab toilet deodorant blocks (crystals) are made from 100% organic material and contain no soap or water soluble components. The crystals gradually evaporate, leaving no residue to contaminate the water. Para dichlorobenzene (PDCB) deodorant blocks are a non-regulated product for transport and storage. PDCB has a short half-life in the atmosphere and is considered readily biodegradable. Recent international studies of the effects of PDCB have concluded that it poses little threat to the environment or to human health when used as intended.