Life cycle assessment of pentachlorophenol-treated wooden utility poles with comparisons to steel and concrete utility poles

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Abstract

A cradle-to-grave life cycle assessment (LCA) was done to identify the environmental impacts related to pentachlorophenol (penta)-treated wooden utility poles. Penta-treated utility poles commonly are used for electricity distribution and transmission, and telecommunications. In addition, this LCA has evaluated the opportunities to reduce the environmental impacts associated with penta-treated poles and has compared the penta-treated pole product to alternative products. A model of penta-treated utility pole life cycle stages was created and used to determine inputs and outputs during the pole production, treating, service life, and disposal stages. Pole production data are based on published sources. Primary wood preservative treatment data were obtained by surveying wood treatment facilities in the United States. Product service life and disposal inventory data are based on published data and professional judgment. Life cycle inventory inputs, outputs, and impact indicators for penta-treated utility poles were quantified per pole. In a similar manner, an inventory model was developed for the manufacture, service life, and disposal of the primary alternative products: steel and spun concrete utility poles. Impact indicator values, including greenhouse gas (GHG) emissions, fossil fuel and water use, and emissions with the potential to cause acidification, smog, ecological toxicity, and eutrophication were quantified for each of the pole products.

The GHG, fossil fuel use, acidification, water use, eutrophication, and ecological toxicity impact indicator values for penta-treated poles are less than those for concrete poles. The GHG, fossil fuel use, acidification, water use, and ecological toxicity impact indicator values for penta-treated poles are less than those for steel poles. The values are about equal for eutrophication. The smog impact from penta-treated poles is greater than the smog impact from both concrete and steel poles.

Introduction

Wood products are susceptible to degradation when left untreated [1] and preservative treatments can extend the useful life of a wood product by 20–40 times that of untreated wood [2] in weather-exposed or wet environments subject to microbial or insect attack. To lengthen the service life of wood products susceptible to degradation, chemical preservation was introduced in the late 1700s and early 1800s. By 1842, wood preservation chemicals included mercuric chloride, copper sulfate, zinc chloride, ferrous sulfate with a sulfide, and creosote [3]. Over the years, industry has modified its wood preservation formulations with new preservatives, thereby meeting consumer preferences and addressing various treated wood applications, such as railroad ties, utility poles, marine pilings, guard rail systems, highway bridge timbers, agricultural fencing, and dimensional lumber.

There are an estimated 120–200 million preservative-treated wood utility poles currently in service in the U.S. Common preservatives used in wood utility pole treatment include chromated copper arsenate (CCA), creosote, and pentachlorophenol (penta). Approximately 62 percent of the total annual preserved utility pole production is estimated to be treated with penta [4].

Penta production began experimentally in the 1930s, with commercial use expanding during the 1940s through the 1980s. Prior to 1987, penta was registered for use as a herbicide, defoliant, molluscicide, fungicide, and insecticide [5]. Since then, penta has been a restricted-use pesticide for use by certified applicators only. Penta is mostly used now in the U.S. as a wood preservative. One of the primary products treated with penta preservative is utility poles.

Penta is mixed with petroleum oil, typically diesel or similar oil cuts, and applied under pressure to the wood products. The American Wood Protection Association [6] includes penta-treating as appropriate for round poles used for utility service.

Previous studies, such as research conducted by the Consortium for Research on Renewable Industrial Materials (CORRIM), have investigated the environmental impacts of wood products. CORRIM's efforts build on a report issued under the auspices of the National Academy of Science regarding the energy consumption of renewable materials during production processes [7]. CORRIM's recent efforts by Johnson et al. [8], [9] and Oneil et al. [10] have focused on an expanded list of environmental aspects necessary to bring wood products to market. Also, the in-service releases from penta-treated utility poles has been the subject of research conducted by Lorber et al. [11], Bulle et al. [12], Winters et al. [13], Murarka et al. [14], and others.

This study investigates the cradle-to-grave life cycle environmental impacts related to penta-treated wooden utility poles used for electricity distribution and transmission, and telecommunications, and uses life cycle assessment (LCA) to quantify such impacts. It covers one treated wood product in a series of LCAs commissioned by the Treated Wood Council (TWC). The series of treated wood product LCAs also covers alkaline copper quaternary (ACQ)-treated lumber, borate-treated lumber, creosote-treated railroad ties, chromated copper arsenate (CCA)-treated marine pilings, and CCA-treated guard rail systems.

Alternatives to treated wood utility poles include spun concrete and steel. The alternative products are produced by many different manufacturers using differing materials and manufacturing processes. The concrete and steel products have approximately the same dimensions as, and generally are used interchangeably with, penta-treated utility poles.

Section snippets

Goal and scope

This study inventories the environmental inputs and outputs attributable to penta-treated utility poles, completes a comparable inventory of steel and concrete utility poles, calculates impact indicators for each product, and makes comparisons between the products. This study was performed using life cycle assessment methodologies in a manner consistent with the principles and guidance provided by the International Organization for Standardization (ISO) in standards ISO 14040 and 14044 [15],

Life cycle inventory analysis

The inventory phase of the LCA developed the inputs from, and outputs to, the environment through each life cycle stage of the product. Inventory development included defining the products, selecting a means to compile data, obtaining and developing applicable life cycle data for life stages, distributing inputs and outputs appropriately between the target and co- or by-products, and summarizing the flow data. The cradle-to-grave life cycle stages considered in this LCA are illustrated in Fig. 1

Selection of the impact indicators

The impact assessment phase of the LCA uses the inventory results to calculate indicators of potential impacts of interest. The environmental impact indicators are considered at “mid-point” rather than at “end-point” in that, for example, the amount of greenhouse gas (GHG) emission in pounds of carbon dioxide equivalent (CO2-eq) was provided rather than estimating end-points of global temperature or sea level increases. The life cycle impact assessment was performed using USEPA's Tool for the

Findings

To assess the processes that result in environmental impact from penta-treated utility poles, impact indicator values were totaled at the four life cycle stages. The impact indicator values at each of the four life cycle stages, and a total for the cradle-to-grave life cycle of penta-treated utility poles, are reported in Table 2.

Impact indicator values were totaled at two stages for concrete and steel products including: (1) the new concrete or steel pole at the utility yard and (2) after

Conclusions

The use of penta-treated utility poles offers lower fossil fuel and water use and environmental impacts than similar products manufactured of concrete and steel, with the exception of emissions with the potential to create smog. Compared to a penta-treated utility pole, and using the assumptions of this LCA, with the understanding that assumptions can vary, use of a concrete utility pole results in approximately four times more fossil fuel use and results in emissions with potential to cause

Acknowledgments

The authors wish to thank the TWC for its funding of this project. The TWC members and their Executive Director, Mr. Jeff Miller, have been integral in its completion. We also thank the internal reviewers, James H. Clark, Mike H. Freeman, and Craig R. McIntyre and the independent external reviewers, Mary Ann Curran, Paul Cooper, and Yurika Nishioka for their support, patience, and perseverance in seeing this project through to completion.

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