Environmental Project, 940 – Survey of dioxin emission from PCP-treated wood – 2 Dioxin and pentachlorophenol treated wood

Survey of Dioxin Emission from PCP-treated Wood

2 Dioxin and pentachlorophenol treated wood

Technical pentachlorophenol has been shown to contain a large number of impurities, depending on the manufacturing method. Pentachlorophenol and its derivatives are therefore generally accepted as precursors of polychloro-dibenzodioxins (PCDDs) and polychlorodibenzofurans (PCDFs) and will naturally contain traces of dioxin (used as abbreviation for PCDDs and PCDFs) developed during the formation process of pentachlorophenol. Other impurities can be polychlorodiphenyl ethers, polychlorophenoxyphenols, chlorinated cyclohexenons and polychlorinated biphenyls (PCBs) [Hansen, 2000]. Technical PCP is typically about 86 % pure [Borysiewicz and Kolsut, 2002]. By now most of the PCP in the PCP-preserved wood still in use in Denmark is expected to have evaporated [Borsholt, 2003], but no precise knowledge exists as to what extent the dioxin has also evaporated. If a parallel is drawn to evaporation of PCB from joint foam for construction purposes, a dioxin evaporation of 10 % of the original content can be expected over a 20-year period. Based on this thesis the annual emission to air from PCP-treated wood was estimated to 0.5 - 20 g I-TEQ/year [Hansen and Hansen, 2003]. The evaporation rate assumed corresponds reasonable well to Dutch assumptions of a half-life of dioxin in wood of 150 years [Bremmer et al 1994].

Pentachlorophenol and its derivatives have been used as wood preservatives in Denmark in a period from approximately 1950 to 1977, where restrictions on the content of dioxin in PCP were introduced [Bylaw, 582-1977]. These restrictions actually functioned as a ban, eliminating by and large all intended use and consumption of PCP in Denmark. Chlorophenols are extremely toxic to the aquatic environment, where chlorophenols can accumulate in sediments. Furthermore infiltration in soil might be a threat to the groundwater resource. Finally PCP and other chlorophenols are a source of formation and dispersal of dioxins and dibenzofurans. Small amounts of dioxins and furans are formed as impurities during production of PCP, and PCP can furthermore be converted into dioxins during combustion processes, primarily waste incineration processes [COWIConsult, 1985]. The health effects by PCP were another reason for the restrictions. The use of PCP in wood preservatives has among other things resulted in cancer deaths in the lumber industry [Alexander, 1996].

The restriction from 1977 was followed by a ban in 1996 on sale of chemical substances and products containing 0.1% PCP or higher concentrations and a ban on sale, import, export and use of goods containing 5 ppm PCP or higher concentrations [Bylaw, 420-1996]. As an exception, countries with ocean coast (France, Ireland, Portugal, Spain and the United Kingdom) can choose to use products with more than 0.1% PCP until the end of year 2008. This exception can only be used in industrial plants for treatment of wood (for outdoors) and waterproofing of fibres and heavy textiles. The total content of HCDD (HexaChloroDibenzoDioxin) in PCP must, however, not exceed 2 ppm [European Commission, 1999].

The use of PCP as wood preservatives has decreased dramatically in Europe since 1980, but it is still used in some scale in Southern Europe for among other things disposable pallets that can be imported to Denmark with goods.