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Preliminary Risk Assessment
Pentachlorophenol ("Penta"), HCB and Dioxin: Questions and Answers

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Current as of April, 2007

  1. What did EPA release?
  2. What is pentachlorophenol and what are its uses?
  3. What were the exposure scenarios included in these preliminary risk assessments?
  4. What are the findings of the preliminary risk assessments?
  5. What special precautions are appropriate for handlers?
  6. Were potential risks to children included in these preliminary risk assessments?
  7. Where is pentachlorophenol in the reregistration eligibility decision (RED) process?
  8. What has been the role of Canada's Pest Management Regulatory Agency (PMRA) in the development of this preliminary risk assessment?
  9. Where can I get further information?

1. What did EPA release?

As part of the six-phase public participation process, EPA did released the Preliminary Risk Assessments (PRAs) for hexachlorobenzene (HCB) and dioxins/furans (CDDs/CDFs), contaminants of pentachlorophenol, for public comment on March 30, 2005. The Preliminary Risk Assessment (PRA) for pentachlorophenol (PCP, or "penta") was released for public comment on November 30, 2004 (closed January 31, 2005). This first preliminary risk assessment only included pentachlorophenol.

The subsequent preliminary assessments focused specifically on potential risks to workers as well as potential ecological and environmental risks from exposure to pentachlorophenol contaminants, HCB and dioxin. The assessments are a cooperative re-evaluation between the U.S. EPA and Health Canada's Pest Management Regulatory Agency (PMRA) under NAFTA. The Federal Register Notice started the 60-day public comment period for the PRAs. The comment period closes on May 31, 2005. The preliminary risk assessments are included in EPA's Docket Number OPP 2004-0402. Also available at this docket site are the first PRA for penta and the comments EPA received. These preliminary risk assessments were developed as part of EPA's process for making reregistration eligibility decisions.

2. What is pentachlorophenol and what are its uses?

Pentachlorophenol (PCP) was one of the most widely used biocides in the U.S. prior to regulatory actions to cancel and restrict certain non-wood preservative uses of pentachlorophenol in 1987. It now has no registered residential uses. Its commercial uses include: utility poles, fences, shingles, walkways, building components, piers, docks and porches, and flooring and laminated beams. Additionally, there are agricultural uses (which are sometimes referred to as "outdoor residential"), i.e., wood protection treatment to buildings/products, and fencerows/hedgerows. Prior to 1987, pentachlorophenol was registered for use as a herbicide, defoliant, mossicide, and as a disinfectant, but now all these uses are cancelled.

The Agency has received and granted requests from the registrants of pesticide products containing pentachlorophenol to terminate certain uses of their products. All non-pressure and non-thermal treatment uses (i.e., spray uses) will be deleted from the registrants' labels. Spray uses for these products were also deleted, effective December 31, 2004. This action leaves only pressure and thermal treatments of pentachlorophenol. The non-pressure/non-thermal treatments in general lead to higher applicator exposures than other uses. In other words, you are not allowed to spray pentachlorophenol, and only pressure and thermal (heat) treatment uses are allowed.

In Canada, pentachlorophenol is used primarily to treat wood poles, piles, bridge timbers, exterior laminated timbers, bridge decking, and fence posts.

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3. What were the exposure scenarios included in these preliminary risk assessments?

The occupational exposure chapter addresses potential exposures and risks of hexachlorobenzene (HCB) and dioxins/furans (CDDs/CDFs), contaminants of pentachlorophenol, to humans who may be exposed in "occupational settings" including: (1) handlers (mixers, loaders, applicators); and (2) individuals who are exposed through postapplication activities. The occupational settings are characterized as wood treatment plants where wood is pressure treated. Therefore, representative occupational handler exposure scenarios focused on treatment plant workers because of their higher exposure to pentachlorophenol. Potential postapplication exposures also may occur in occupational settings such as wood pressure treatment plants where treated lumber is handled for QA/QC testing, or storage/transport, or in commercial or institutional outdoor settings where the wood is fabricated into structures and professionally installed.

The ecological risk chapters discuss environmental exposures and risks to aquatic and terrestrial wildlife. The terrestrial assessment considered exposure via food items from soil contaminated with HCB and dioxins/furans leached from structures made from pentachlorophenol-treated wood. The aquatic assessment considered on exposure to HCB and dioxins/furans leached into the surrounding water from pentachlorophenol-treated wood. Exposure estimates were compared to available toxicity endpoints for various organisms in order to estimate risks.

4. What are the findings of the preliminary risk assessments?

Because these are preliminary assessments, it is premature for EPA to reach conclusions about the potential risks from exposure to HCB and dioxins/furans resulting from the use of pentachlorophenol. While EPA has identified some potential risks of concern, the risk estimates provided in this assessment are of a preliminary nature and subject to refinement. The process that EPA uses to review chemicals through reregistration is intended to gather additional information and input from the public and stakeholders about exposure and risk that will be used to revise the risk estimates. Based on such input through this public comment period, EPA will develop a revised risk assessment and will be able to determine whether or not risk mitigation measures are needed. Consequently, the potential risks discussed in the preliminary risk assessment may change after the Agency has received and evaluated public comment received during the comment period. See EPA docket OPP-2004-0402 for the complete preliminary risk assessments.

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5. What special precautions are appropriate for handlers?

General precautions for handling treated wood include always washing hands thoroughly after contacting treated wood, especially prior to eating and drinking, and ensuring that food does not come into direct contact with any treated wood. Workers should follow these recommendations: wear gloves when handling wood, wear goggles and dust-masks when sawing and sanding, and never burn treated wood.

6. Were potential risks to children included in these preliminary risk assessments?

EPA looked into this question and determined that exposure scenarios for children are highly unlikely, and therefore an assessment was not needed.

7. Where is pentachlorophenol in the reregistration eligibility decision (RED) process?

The wood preservatives containing pentachlorophenol are undergoing a six-phase RED process. This action opens Phase 3, which is the public comment phase, with the release of the preliminary risk assessments (PRAs). During Phase 4, EPA considers comments and revises the risk assessments, as necessary. During Phase 5, EPA releases the revised risk assessment and discusses risk mitigation options and solicits the public's comments. Finally, during Phase 6, the Agency issues the final RED. The pentachlorophenol RED is scheduled for winter of 2007.

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8. What has been the role of Canada's Pest Management Regulatory Agency (PMRA) in the development of this preliminary risk assessment?

These preliminary risk assessments are a cooperative re-evaluation between the U.S. EPA and Health Canada's Pest Management Regulatory Agency under the North American Free Trade Agreement. Both countries have contributed to the study review and peer review process. Exposure data used in the preliminary risk assessments were collected from both US and Canadian wood-treatment facilities and both countries are participating in the public comment process. As the assessments are finalized, EPA will continue to work closely with Canada since the goal of these efforts is to develop science and regulatory conclusions amenable to both agencies.

9. Where can I get further information?

For more information, email harris.monisha@epa.gov.

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