1. Introduction

1.1 Background

• waste incineration

• metallurgical industries, including smelting, refining and recycling

• industrial and domestic coal and wood combustion

• exhaust emissions from vehicles running on diesel and unleaded petrol

• controlled burn-offs

• uncontrolled and accidental fires

• pesticide use.

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 (especially those at the top of the food chain, such as predatory birds and marine mammals) and humans. In view of this international concern, the Ministry for the Environment commenced a national Organochlorines Programme² 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.

1.2 Organochlorine pesticides in New Zealand

A number of organochlorine pesticides were widely used across a variety of industry sectors (agriculture, horticulture, timber processing) in New Zealand from the late 1940s to the late 1980s. These pesticides included herbicides and insecticides such as DDT, dieldrin, chlordane, 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) and pentachlorophenol (PCP). Many of these chemicals, at a technical or commercial grade specification, contained trace levels of impurities. Technical grade PCP typically contained ‘dioxin impurities’. As a result, at locations where PCP was stored or used, there is the potential for the soil to be contaminated with PCP and the dioxin impurities.

PCP in New Zealand

Until its voluntary withdrawal by the timber industry in 1988, PCP (or its sodium salt NaPCP) was used in the industry in a variety of treatment processes. The use of PCP on a site varied from a single occasion up to approximately 35 years. On many sites the locations where the chemicals were used, or where the treated timber was stored, were unpaved. Consequently, spills of chemicals or drippage from freshly treated timber have resulted in soil contamination by PCP and dioxins. To assist with the management of contaminated timber treatment sites, health and environmental guidelines were published in 1997 (Ministry for the Environment and Ministry of Health, 1997).

Use of the term PCP in this report

Unless otherwise specified, the use of the term PCP in the text and tables of this report means pentachorophenol as measured in soil samples irrespective of the chemical form used to treat timber.

PCP as a preservative

PCP in diesel oil was used as a permanent timber preservative (in telegraph poles, railway sleepers, etc.), applied either through a pressure treatment process (known as the Rueping process) or through hot and cold dipping in a bath. The Rueping process was used at one site only, Waipa. Although there was a second plant in Christchurch, there is no record of it being used. Three sites used the hot and cold bath method. The concentration of PCP in both of these processes was 5% weight per volume (w/v).

NaPCP as a preservative

A preservative formulation of sodium pentachlorophenate (NaPCP) in water (Immutan B and Tanalith FMP) was also used, again in a pressure treatment process in the late 1960s to mid-1970s. The concentration of pentachlorophenate in the treatment solution was relatively low at 0.06-0.14% w/v PCP. Much less preservative was required for internal building timbers, so lower amounts of preservative were used per unit of wood compared with the above processes. Because the use of this process was not widespread (estimated to be fewer than 20 sites) and only a relatively small amount of timber was treated by this method, contamination associated with this process has not been investigated in this study.

NaPCP as an antisapstain fungicide

Pine species are susceptible to attack by fungi that feed on wood sap, and their excretion may cause discolouration of the timber. NaPCP was used to prevent fungal attack on the timber while it was being dried before further processing. Freshly sawn (green) timber had antisapstain fungicide applied, either in a dip bath or in a spray tunnel as it travelled from the saws to a sorting table. Logs, posts and poles were treated in dip baths or spray tunnels, or by hand or mechanical spraying. The concentration of PCP for sapstain control was generally 0.5% w/v, although in some hand-spraying operations the concentration was up to 1.0% w/v.

In the boron diffusion process, NaPCP was also added to the boron treatment chemicals (applied in a dip bath or spray tunnel). Because the majority of this timber had already been treated in the ‘green chain’ antisapstain process, the concentration of PCP in the boric treatment solution was only 0.2% w/v. If the timber had not been treated at the green chain stage, the concentration may have been raised to 0.5% w/v.

1.3 Purposes of the study

In 2000 the Ministry for the Environment published an inventory of dioxin sources covering a wide range of processes and activities (Ministry for the Environment 2000). This inventory included an estimate of the dioxin reservoir present in soil at sawmill sites. To estimate the reservoir, the soil burdens were calculated for each area at the sites where contaminant concentration data were available. These burdens were then summed to give a total dioxin burden per site, and this burden was multiplied by the estimated number of sawmill sites in the country. In this way, the dioxin reservoir at sawmill sites was estimated to be 310 g, measured as toxic equivalents or TEQ (see section 2.1). It was noted then that this estimate was based on limited data with inherent uncertainty over the national figure.

The current study was initiated by the Ministry for the Environment to provide more definitive data on the level of dioxin contamination at sawmill sites and to better assess the risks such sites may pose.

The four key tasks of the study were to:

1. collect more reliable and nationally representative data on the concentration of dioxins at sawmill sites

2. revise the existing estimate of the dioxin reservoir at sawmill sites

3. detail the types of environmental and risk management conditions that may be found at sawmill sites, and develop a risk profile of these sites

4. identify options for risk reduction measures for residual contamination associated with past usage of PCP at sawmill sites in New Zealand.

1.4 Scope and content of this report

The remainder of this report is structured as follows.

Chapter 2 gives brief background information on dioxins, including their toxicity and the standard means of reporting dioxin concentration using toxic equivalence factors. It then provides a summary of the data on dioxin contamination that was available prior to this study.

Chapter 3 provides details on the study design and methodology.

Chapter 4 presents the results of the site investigation for sites that were classified as small, medium or large users of PCP. The study information is then used to revise the estimate of the dioxin reservoir at sawmill and timber treatment sites. This estimate takes into consideration areas where contamination may have occurred but that were not specifically investigated in the studies, as well as the degree of remediation that may already have taken place.

Chapter 5 looks at the potential risks that may arise from the contaminant levels found. The risk from off-site migration and entry into the food chain is assessed to be low, so the focus is placed on potential on-site risks for three main land uses: ongoing sawmill/industrial use, residential use and agricultural use.

Chapter 6 then examines options for risk reduction for these three uses.

Chapter 7 provides conclusions drawn from the study and the investigation results, and discusses the limitations of the study results.