A preservative is a natural or synthetic chemical that's added to products such as foods, pharmaceuticals, paints, biological samples, wood, etc. to prevent decomposition by microbial growth or by undesirable chemical changes. Preservatives in wood Preservatives may be added to wood to prevent the growth of fungi as well as to repel insects and termites. Typically arsenic, copper, chromium, borate, and petroleum based chemical compounds are used. For more information on wood preservatives, see… (More on Preservatives)