Environmental Project, 940 – Survey of dioxin emission from PCP-treated wood

Survey of Dioxin Emission from PCP-treated Wood

7 Conclusion

Pentachlorophenol-preserved wood has been discussed as a source of dioxin emission to the Danish society. The Substance Flow Analyses made on dioxin in Denmark have until now estimated the emission to air at 0.5 - 26 g I-TEQ/year [Hansen and Hansen, 2003]. The emission from PCP-preserved wood can therefore be both a quite substantial and a less significant source of the total Danish dioxin emission. Especially the question regarding evaporation from the PCP-preserved wood is unclear, as only the dioxin concentration in newly PCP-treated wood has been examined in a few international studies.

It is expected that there are two sources of dioxin from PCP-preserved wood: Construction wood that has been treated with PCP preservation in the period of 1950 to approximately 1977 and different types of wood preserved with PCP and imported to Denmark. The present import of PCP-preserved wood is expected primarily to be disposable pallet boards from Southern Europe which have been anti-sap-stain controlled with PCP. These two sources of dioxin have therefore been examined in the present study.

Because of the number of available analyses the project have only been able to give an indication of the size of the two sources, but succeeds in documenting that especially construction wood should be regarded as a notrworthy source of dioxin emission.

Imported PCP preserved wood
The samples of disposable pallet boards were selected only on the basis of the country of origin the goods were imported from, as it would be very difficult to trace the history of the pallet boards. It was not known whether the pallet boards actually contained PCP. It was therefore quite surprising that PCP could be traced in 6 out of the 10 selected pallet board samples. The use of PCP for anti-sap-stain control is therefore still regarded to be quite common both in Spain, Portugal and France - as PCP was found in samples from all three countries. The concentrations of PCP in the pallet board samples were however considerably lower than previously estimated concentrations, as the measured values were in the range of 20 - 164 μg/kg wood (90 % confidence level), and the previously used concentrations for industrial, preserved wood were in the range of approximately 0.1 - 0.2 g/kg wood. Only one dioxin analysis was made on pallet board. The sample with the highest PCP concentration was selected for the analysis. The measurement showed a dioxin content of 4.6 ng I-TEQ/kg wood, which is low compared to the construction wood.

Although the present import of dioxin and PCP with PCP preserved wood probably is small the emission of dioxin to air must be expected basically to be determined by the quantity of dioxin still present in PCP-preserved wood imported during the 1980'ties and the 1990'ties. The emission has consequently been recalculated to 0.03 – 5 g I-TEQ/year, which is only slightly less than the emission figure of 0.03 – 6 g I-TEQ/year previously assumed.

The wood in question is used for construction purposes and will by time slowly will be disposed of resulting in that the emission of dioxin also slowly by time should be expected to be reduced and eliminated.

It is emphasised that the above calculations must be taken as extremely uncertain and should be regarded as an indication only of the relevant order of magnitude for the dioxin flows in question.

Construction wood preserved with PCP in Denmark
The construction wood samples have been collected based on mini-interviews with house owners living in houses constructed in the period of 1960 - 1972. The chance of finding dioxin in these samples was therefore better, and dioxin was actually found in all five analysed samples. The measured concentrations range between 84-1079 ng I-TEQ/kg wood.

Assuming that the measured concentrations follows a normal distribution the 90 % confidence level (the concentrations representing the interval within which 90 % of all concentrations are likely to be registered) is defined as interval of 34 - 793 ng I-TEQ/kg wood. This corresponds to a total dioxin content of 42 - 974 g I-TEQ in the PCP-preserved construction wood that is left in Denmark by 2003.

Assuming an evaporation rate of 0.5 % of the actual dioxin content in the wood the dioxin emission from the PCP-treated construction wood in Denmark can be estimated to 0.2 - 4.9 g I-TEQ/year in 2003.

This estimate corresponds reasonable well to the estimate from [Hansen, 2003] on 0.5 - 20 g I-TEQ/year for the year 2000, considering inter alia that the quantity of PCP-treated wood still in use in Denmark is assumed to have been lowered by around 37 % between 2000 and 2003.

Based on the experiences from the present project the total estimate for dioxin emission from PCP-treated wood can be summed up to 0.23 - 9.9 g I-TEQ/year. This is lower than the earlier used estimate of 0.5 - 26 g I-TEQ/year [Hansen, 2000] and [Hansen and Hansen, 2003]. In spite that the interval for emission of PCP-preserved wood has been reduced, PCP-treated wood must still be regarded as a noteworthy contribution to the total dioxin emission in Denmark.