Wood preservation facilities, pentachlorophenol pressure: chapter E-1

1. Production and Use

Pentachlorophenol¹(PCP) was first used as a wood preservative in 1936 (1). The biological properties of PCP have resulted in its use as an antimicrobial agent in industrial cooling systems and papermaking, and as a fungicide in protein-based latex paints (2). Agriculture Canada restrictions in 1981 limited the use of PCP for preservation of outdoor wood products. PCPis currently used for pressure treatment of wood products (PCPP) such as telephone and electrical utility poles, cross-arms, posts and construction timbers (3). Over 90% of all PCPP is used for utility pole preservation. PCP use by the wood preservation industry depends primarily on the size of the pole and cross-arm markets: chromated copper arsenate (CCA) has partially replaced PCP in the utility pole market, and the PCPrailway tie market has been converted to creosote/oil treatments, leading to a decline in use since 1981 (4). Table 1 provides an overview of PCP use at Canadian pressure treatment facilities.

PCP is prepared by reacting chlorine with phenol in the presence of a catalyst at high temperatures. PCP was last manufactured in Canada in 1983. It is now obtained from only one U.S. manufacturer who supplies it in the form of solid blocks (900 kg/2000 lbs) or liquid bulk . The petroleum oils used as carriers for PCP are purchased generally from Canadian sources.

The pressure-impregnated PCP/oil mixture is retained by the wood, and its bio-effectiveness protects the wood against fungi and insects. In addition to functioning as a carrier of PCP, the oil also provides extra protection against moisture content changes, leading to greater wood stability and resistance to splitting. For utility pole use it has the additional advantage of providing resistance to electrical currents and facilitating the climbing of poles by line personnel.

The CSA O80 Series of Standards specifies requirements related to the preservation and fire retardance of wood through chemical treatment (pressure), which includes PCP-treated products. (5) Treatment conditions must be calibrated to yield the target retention levels described on the pesticide label.