Executive Summary

There is worldwide concern about organochlorine contaminants in the environment because even low concentrations are reported to contribute in the long term to significant risks to the health of animals and humans. In view of this concern, the Ministry for the Environment commenced a national Organochlorines Programme to carry out research, assess exposure and health risks, and consider issues such as clean-up targets and emission control standards. This report, Assessment of Dioxin Contamination at Sawmill Sites, is part of this broader programme of work on dioxin and organochlorine issues.

The purpose of the current study was to provide the Ministry for the Environment with a revised national estimate of dioxin contamination at sawmill sites and to identify options for reducing risk at these sites. From a review of regional council information and the Timber Preservation Authority files, a total of 255 sawmills are thought to have used NaPCP or PCP, and these have been classified as small, medium or high users of PCP based on the available information.

In this study, PCP and dioxin analyses were undertaken on soils sampled from 17 sawmills within the vicinity of the historical application of PCP-containing solutions (antisapstain dip or spray, sorting table, boric dip or spray, chemical storage or mixing area). The sawmills sampled represented small, medium and high PCP users, and the data for each category have been extrapolated for the number of sites in each category.

The total amount of dioxin remaining in soil collectively from the 255 sawmill sites in New Zealand was estimated at November 2002 to be:

• 80-250 grams dioxin toxic equivalents¹ from NaPCP use

• 172 grams dioxin toxic equivalents from PCP in oil use.

These estimates revise those previously published in the New Zealand Inventory of Dioxin Emissions to Air, Land and Water, and Reservoir Sources (Ministry for the Environment, 2000).

On a site-by-site basis, risks to human health and the environment from soil contaminated by PCP and dioxin are associated predominantly with the sites (approximately 35) that were relatively large users of PCP. Investigations of some of these sites have shown (although this is not reported in this study) that PCP and dioxin have migrated off site and contaminated, respectively, water bodies and sediment (dioxin is tightly bound to particulate matter in the absence of oil), including two sites where PCP in oil was used as a preservative (Waipa and Hanmer Springs).

Attention to health risk assessment is strongly indicated for such sites if a change from an industrial use to residential use or a life-style block were proposed. Given the scale of operations on these sites and their locations, such changes in land use are unlikely.

Unless the site was a large user of PCP, investigations of PCP contamination by the timber industry and regional councils indicate that little off-site migration of PCP (and by implication dioxins) is likely in either groundwater or surface water. Thus, on a site-by-site basis, if little potential for dioxin entry to the food chain or the aquatic environment is apparent, the potential risk to human health is confined to direct exposure to the soil where PCP has been used.

A database has been compiled of sites that used PCP in New Zealand. This database has been provided to regional councils on a region-by-region basis to assist local government to monitor the use of these sites, particularly in situations involving a change of land use.