Chlorinated dibenzodioxins and pentachlorophenol.

Pentachlorophenol is a registered antimicrobial agent whose principal use is for the preservation of wood. Typical commercial pentachlorophenol contains a variety of substances which are considered to be "inactive" from the aspect of antimicrobial efficacy. Consequently, pentachlorophenol is sold as an antimicrobial agent with 95%o active ingredients and 5%o "inert" ingredients. Analysis of acceptable commercial pentachlorophenol is shown in Table 1. The "caustic insolubles," sometimes referred to as the "nonphenolic or neutral impurities," include chlorinated dibenzo-p-dioxins and chlorinated dibenzofurans (1). Recently developed analytical technology has allowed quantitation of hexachlorodibenzop-dioxins and octachlorodibenzo-p-dioxin in pentachlorophenol. Portrayed in Table 2 are concentration ranges for these two chlorodibenzo-p-dioxins in samples of currently available commercial grade pentachlorophenol. Techniques capable of detecting 0.05 ppm showed no 2,3,7,8-tetrachlorodibenzo-p-dioxin in any sample of pentachlorophenol examined by us. The absence of this compound in pentachlorophenol is not surprising, because the appropriate precursors for its formation are not present.