Guide for Minimizing 

the Effect of 

Preservative-Treated 

Wood on Sensitive 

Environments 

Stan T. Lebow 

Michael Tippie 

United States

Department of 

Agriculture 

Forest Service 

Forest 

Products 

Laboratory 

National Wood 

in Transportation 

Information 

Center 

General 

Technical 

Report 

FPL−GTR−122

 

In cooperation 

with the 

United States 

Department of 

Transportation 

Federal 

Highway 

Administration 
Abstract 

Preservative-treated wood is often used for construction of 

highway and foot bridges, wetland boardwalks, and other 

structures in or over water or sensitive environments. In these 

applications it is important that release of preservative from 

the wood into the environment is minimized. This publication addresses this concern by describing the various types of 

pressure-treated wood, reviewing recent research on the 

environmental impacts of pressure-treated wood, and discussing methods of minimizing potential environmental 

impacts. Recent research indicates that wood treated with 

these preservatives does release small amounts of chemical 

into the environment immediately adjacent to the treated 

structure, although no adverse biological impacts were observed. Environmental releases from treated wood can be 

minimized with appropriate treatment practices. These practices include fabricating members before treatment and specifying that the wood be treated using methods that ensure 

chemical fixation and prevent the formation of surface residues or bleeding. Guidance to specifying such treating practices are offered in this report and in sources such as the Best 

Management Practices developed by the Western Wood 

Preservers’ Institute. Also, responsible construction practices 

such as storage of treated wood under cover and containment 

and collection of construction residue can further reduce the 

possibility of negative environmental impacts. As with any 

other construction material, careful specification and responsible use of treated wood will optimize its performance. 

Keywords: preservative-treated wood, sensitive environments, environmental impacts, leaching, treatment practices, 

fixation, construction practices 

February 2001 

Lebow, Stan T.; Tippie, Michael. 2001. Guide for minimizing the effect of 

preservative-treated wood on sensitive environments. Gen. Tech. Rep. FPL–

GTR–122. Madison, WI: U.S. Department of Agriculture, Forest Service, 

Forest Products Laboratory. 18 p. 

A limited number of free copies of this publication are available to the 

public from the Forest Products Laboratory, One Gifford Pinchot Drive, 

Madison, WI 53705–2398. Laboratory publications are sent to hundreds 

of libraries in the United States and elsewhere. 

The Forest Products Laboratory is maintained in cooperation with the 

University of Wisconsin. 

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origin, sex, religion, age, disability, political beliefs, sexual orientation, or 

marital or familial status. (Not all prohibited bases apply to all programs.) 

Persons with disabilities who require alternative means for communication 

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Room 326-W, Whitten Building, 1400 Independence Avenue, SW, Washington, DC 20250–9410, or call (202) 720–5964 (voice and TDD). USDA 

is an equal opportunity provider and employer. 

Acknowledgment 

The authors acknowledge the support of the U.S. Department 

of Transportation, Federal Highway Administration, for this 

project. 

Contents 

 Page

Introduction............................................................................1

Types of Treated Wood .........................................................1

Water-Type Wood Preservatives .......................................1

Oil-Type Wood Preservatives............................................3

Restricted Use Pesticides ...................................................4

Prior Research on Environmental Impacts.............................4

Treatment Practices................................................................4

Prefabrication.....................................................................4

Treatment Processes ..........................................................5

Post-Treatment Processing: Fixation of Waterborne 

Preservatives ......................................................................6

Construction Practices ...........................................................8

On-Site Storage of Treated Wood......................................8

Minimizing Effects of Construction Debris .......................8

Field Preservative Treatments of Cuts and Bore Holes .....9

Use of Absorbent Materials With Oil-Type 

Preservatives ....................................................................10

Water Repellants and Stains ................................................10

Factory-Applied Water Repellants and Stains .................10

Field-Applied Water Repellants and Stains .....................10

Cleaning...........................................................................11

Summary..............................................................................11

References............................................................................11

Appendix A—Prior Research on Environmental Impacts ...12

Appendix B—Preservative Retention Levels.......................14

Appendix C—Guidelines for Minimizing Oil-Type Wood 

Preservative Migration ........................................................15

Appendix D—Method for Determining the Pressence of 

Hexavalent Chromium in Treated Wood ............................17
Guide for Minimizing the Effect 

of Preservative-Treated Wood 

on Sensitive Environments 

Stan T. Lebow, Research Forest Products Technologist

Forest Products Laboratory, Madison, Wisconsin 

Michael Tippie, Engineer 

Mt. Hood National Forest, Sandy, Oregon

Introduction 

Preservative-treated wood is commonly used for construction 

of highway bridges, foot bridges, wetland boardwalks, and 

other applications where the wood is placed in or over water. 

Many of these applications place the wood in pristine or 

sensitive ecosystems. Treated wood is used for these types of 

applications because it is economical, blends well with the 

environment, is relatively easy to install, and is durable. The 

wood is durable because the chemicals in the preservative are 

toxic to decay fungi and insects. However, these same 

chemicals that are beneficial in protecting the wood are also 

potentially toxic to aquatic organisms. This has caused some 

concern that chemicals might leach out of the wood and 

accumulate in the environment to harmful levels. Both field 

and administrative personnel are often asked to justify the 

choice of treated wood as a construction material, and there 

is sometimes pressure to reduce or eliminate the use of 

treated wood in favor of products that are perceived to be 

more environmentally acceptable. The issue has been difficult to resolve because of the lack of data on leaching and 

biological impacts of wood preservatives, particularly under 

in-service conditions (Tippie, 1993, unpublished report). The 

Federal Highway Administration, under a cooperative National Timber Bridge Research Program, has funded research 

and publications to address these environmental concerns. 

This report describes the various types of pressure-treated 

wood, reviews recent research on environmental impacts of 

treated wood used in sensitive environments, and discusses 

methods of minimizing potential environmental impacts. 

Types of Treated Wood 

With the exception of naturally durable species such as cedar 

and redwood, wood used in outdoor applications should be 

pressure treated with preservatives if it is expected to last 

more than a few years. Wood preservatives have been used in 

the United States for more than a hundred years, but in the 

past few years, several new wood preservatives have been 

developed. Consumers are sometimes confused about what 

is in their pressure-treated wood or what type of pressuretreated wood they should be using. Identification of wood 

preservatives can be simplified by first classifying them as 

either water- or oil-type, depending on the chemical composition of the preservative and the carrier used during the 

treating process. 

Water-Type Wood Preservatives 

Chromated copper arsenate (CCA-C), ammoniacal copper 

zinc arsenate (ACZA), ammoniacal copper citrate (CC), 

alkaline copper quaternary compounds (ACQ), copper azole 

(CBA), and copper dimethyldithocarbamate (CDDC) are 

waterborne preservatives that react with or precipitate in the 

wood substrate and become “fixed” so that they resist leaching. Because waterborne preservatives leave a dry, paintable 

surface, they are commonly used in residential applications 

such as decks and fences (Fig. 1). They are also widely used 

for treatment of poles, piling, and timbers. These waterborne 

preservatives are primarily used to treat softwood species and 

are very effective for this application. However, because 

their cellular structure is different, hardwoods treated with 

waterborne preservatives may not be adequately protected in 

some types of exposures. Water-type wood preservatives can 

sometimes increase corrosion of unprotected metal, and so 

all metal fasteners used with treated wood should be hotdipped galvanized or stainless steel. Borates are another type 

of waterborne preservative, but borate preservatives do not 

fix in the wood and thus are readily leached if exposed to 

rainfall or standing water. 
2 

Chromated Copper Arsenate 

Chromated copper arsenate, Type C (CCA-C) is the most 

widely used wood preservative in the United States. It contains chromium, copper, and arsenic. CCA-C protects against 

attack by decay fungi, insects, and most types of marine 

borers. CCA-treated wood is used in decks, fences, poles, 

piling, and bridge timbers. It is sometimes difficult to obtain 

adequate penetration of CCA-C in difficult-to-treat species 

such as Douglas-fir. CCA-C treated wood is widely available 

at retail lumberyards and is sold under many different trade 

names. CCA-treated wood typically has a light green color 

but is often stained or dyed by the manufacturer to various 

shades of brown. It may also include a water-repellant treatment, which helps prevent splitting and checking when the 

wood is used on a flat surface, such as decking. CCA-treated 

wood has little or no odor. 

Ammoniacal Copper Zinc Arsenate 

Ammoniacal copper zinc arsenate (ACZA) contains copper, 

zinc, and arsenic. ACZA is a refinement on the original 

formulation, ACA. ACZA protects against attack by decay 

fungi, insects, and most types of marine borers. Its uses are 

very similar to those of CCA-C and include treatment of 

poles, piling, and timbers. Because of its ability to penetrate 

Douglas-fir and other difficult-to-treat wood species, it is 

most widely used on the West Coast. The color of the treated 

wood is dark brown to bluish green. The wood initially has a 

slight ammonia odor, but this dissipates soon after treatment. 

Alkaline Copper Quat 

Alkaline copper quat (ACQ) is one of several recently developed wood preservatives. It contains copper and a quaternary 

ammonium compound. ACQ protects against decay fungi and 

insects but has not been standardized for use in seawater 

applications. There are two types of ACQ: ACQ Type B 

(ACQ-B) and ACQ Type D (ACQ-D). ACQ-B is formulated 

using ammoniacal copper, and like ACZA, ACQ-B is able to 

penetrate Douglas-fir and other difficult-to-treat wood species and is marketed primarily on the West Coast. ACQ-Btreated wood has a dark greenish brown color. ACQ-D is 

formulated using amine copper, which gives the wood a light 

brown color. It does not penetrate difficult-to-treat wood as 

well as ACQ-B and is most commonly used for treatment of 

thick sapwood pine species. 

Ammoniacal Copper Citrate 

Ammoniacal copper citrate (CC) is a recently developed 

preservative that contains copper and citric acid. The copper 

protects against decay fungi, insects, and marine borers, and 

the citric acid aids in the distribution of copper within the 

wood. Because CC was developed very recently, it is not yet 

widely used and may not be available in some areas. As with 

Figure 1—Wood treated with waterborne preservatives is often used for decking, such as 

in this wetland boardwalk. 
3 

other preservatives containing ammonia, CC is able to penetrate difficult-to-treat species like Douglas-fir. The color of 

the treated wood varies from light green to dark brown. The 

wood initially has a slight ammonia odor, but this dissipates 

soon after treatment. 

Copper Azole 

Copper azole (CBA) is a recently developed wood preservative that contains copper, boric acid, and tebuconazole. 

These three active ingredients work together to protect 

against decay fungi and insects. CBA has not been standardized for use in seawater. Because CBA was developed very 

recently, it is not yet widely used and may not be available in 

some areas. CBA is able to provide good treatment for 

Southern Pine and hemlock–fir species groups but has not 

been standardized for use in Douglas-fir. CBA-treated wood 

has a uniform greenish brown color and little or no odor. It 

can be painted or stained. 

Copper Dimethyldithocarbamate 

Copper dimethyldithocarbamate (CDDC) is a reaction product formed within the wood after treatment with two different 

treating solutions. It contains copper and sulfur compounds. 

CDDC protects against decay fungi and insects, but it has not 

been standardized for use in seawater. Because CDDC was 

developed very recently, it is not yet widely used and may 

not be available in some areas. CDDC is standardized for 

treatment of Southern Pine and some other pine species. 

CDDC-treated wood has a brown color and has little or no 

odor. 

Borate Preservatives 

Borate preservatives are salts such as sodium octaborate, 

sodium tetraborate, and sodium pentaborate that are dissolved in water. Borates are effective preservatives against 

decay fungi and insects. Borate preservatives are diffusible, 

and with appropriate treating practices, they can achieve 

excellent penetration in species that are difficult to treat with 

other preservatives. However, the borate in the wood remains 

water soluble and readily leaches out in soil or rainwater. 

Borate-treated wood can be used only in applications where 

the wood is kept free from rainwater, out of standing water, 

and away from ground contact. An example of such a use is 

in the construction of wooden buildings in areas of high 

termite hazard. Borate-treated wood is odorless and colorless 

and may be painted or stained. 

Oil-Type Wood Preservatives 

The most common oil-type preservatives are creosote, pentachlorophenol, and copper naphthenate. Oil-type preservatives 

are commonly used for applications such as utility poles, 

bridge timbers, railroad ties, pilings, and laminated beams 

such as for bridge applications (Fig. 2). They are less 

Figure 2—Oil-type preservatives are often used for treatment of glulam beams, such as 

in this bridge.
4 

frequently used for applications that involve frequent human 

skin contact or for inside dwellings because they may be oily 

or have a strong odor. Because of their oily nature, these 

preservatives also act as water repellants and can help to 

prevent checking and splitting. 

Creosote 

Creosote is made from coal tar, which is a byproduct of the 

carbonization of coal during coke production. Unlike the 

other oil-type preservatives, creosote is not usually dissolved 

in oil, but it does have properties that make it look and feel 

oily. Creosote contains a chemically complex mixture of 

organic molecules, most of which are polycyclic aromatic 

hydrocarbons (PAHs). Creosote is effective in preventing 

attack by decay fungi, insects, and most marine borers. Creosote is widely used in railroad ties, utility poles, bridge timbers, and piling. It has a dark brown–black color with an oily 

surface and strong odor. It is very difficult to paint, stain, or 

seal. It is not recommended for use inside dwellings or areas 

where it may come into frequent contact with human hands, 

such as handrails 

Pentachlorophenol 

Pentachlorophenol is a crystalline solid that can be dissolved 

in different types of oils. Pentachlorophenol is very effective 

against fungi and insects but does not protect well against 

ocean marine borers. It is widely used to treat utility poles, 

bridge timbers, laminated beams, and fresh water and 

foundation piling. The appearance of pentachlorophenoltreated wood depends greatly on the type of oil that it is used 

as a carrier solvent. The wood may have a very light brown 

color and dry surface if a light oil is used or a dark brown 

color and somewhat oily surface if a heavy oil is used. Pentachlorophenol-treated wood is generally more durable if a 

heavy oil is used, so light oil is most often used above ground 

or in covered structures. Pentachlorophenol itself is odorless, 

but the odor of the carrier oil may be noticeable near the 

treated wood. Pentachlorophenol-treated wood should not be 

used inside dwellings and is generally not recommended for 

areas where it may come into frequent contact with human 

hands, such as handrails. It is difficult to paint or stain unless 

the pentachlorophenol was pressure treated using a light oil 

as the carrier solvent. 

Copper Naphthenate 

Copper naphthenate is a mixture of naphthenic acids and 

copper salts dissolved in oil. It is effective against decay 

fungi and insects but is not recommended for use in marine 

applications. Copper naphthenate is not as widely used as 

creosote or pentachlorophenol, but it is used for the treatment 

of utility poles and in highway construction. Like pentachlorophenol, the properties of copper naphthenate are dependent on the type of oil used as the carrier. The most 

commonly used oils are fuel oil and mineral spirits. The color 

of the treated wood varies from light brown to dark green, 

depending on the type of oil and the treating process. The 

odor of the oil may be noticeable near the treated wood. It is 

difficult to paint or stain unless the copper naphthenate was 

treated using a light carrier solvent. Copper naphthenate is 

not a restricted-use pesticide and can be purchased at retail 

lumberyards and hardware stores. It is widely applied as a 

field treatment on end cuts or holes bored into pressuretreated wood during construction. 

Restricted Use Pesticides 

Some wood preservatives are classified as restricted use 

pesticides (RUP) by the U.S. Environmental Protection 

Agency. The restricted use classification means that only 

certified applicators (that is, pressure treatment facilities) can 

treat wood with these preservatives. Consumers can no 

longer purchase these preservatives for field applications. 

Currently, the RUP preservatives are creosote, pentachlorophenol, and any preservative containing inorganic arsenic 

(CCA-C and ACZA). 

Prior Research on 

Environmental Impacts 

Until relatively recently, there had been little research on 

release of wood preservatives from in-service structures or 

on the environmental consequences of those releases. However, within the past decade, several studies on this subject 

have been done (Appendix A). In each of these studies, the 

various types of treated wood did release measurable 

amounts of preservative into the environment. In most cases, 

the levels of environmental accumulation were low and 

limited to close proximity to the treated structure. Adverse 

biological impacts were either not observed (boardwalk and 

bridge studies) or confined to close proximity to the treated 

structure (creosote-treated dolphin piling). These studies 

demonstrate that treated wood can be used in and over 

aquatic environments with little or no adverse biological 

impacts. However, it is also apparent that some release of 

preservative does occur and that reasonable precautions 

should be taken to ensure that these releases are minimized. 

The remainder of this paper discusses some of the treatment, 

handling, and construction practices that can be used to 

minimize the environmental impacts of treated wood.

Treatment Practices 

Prefabrication 

Whenever possible, it is desirable to cut wooden members to 

length and perform boring and other machining processes 

prior to pressure treatment. This prefabrication increases the 

durability of the treated structure, as well as helping to 

minimize environmental impacts. The practice enhances 

durability because there is less field fabrication, which often 

breaks the treated shell and exposes untreated wood. 
5 

Reducing the amount of field fabrication also helps prevent 

the discharge of treated sawdust, drill shavings, and other 

construction debris into the environment at the construction 

site. It also minimizes the need for treatment with a topical 

wood preservative at the construction site. The exact dimensions of members and location of connectors are not always 

known, but in many cases, it is possible to perform some 

prefabrication. Decking and rail posts are examples of 

members that can often be cut or bored prior to pressure 

treatment. 

Treatment Processes 

The pressure preservative treatment process greatly impacts 

the subsequent release of preservative from the treated wood. 

Although treatment processes may seem to be solely the 

responsibility of the treater, they are also greatly influenced 

by the specifications and demands of the project engineer 

and contractor. 

Over-Treatment 

One example of customer influence on the treating process is 

the retention, or loading, of preservative in the wood. Retentions that are specified by standards such as the American 

Wood-Preserver’s Association (AWPA 2000) (for example, 

0.4 lb/ft3

 CCA-C for treated wood to be used in contact with 

the ground) have been shown to be more than sufficient to 

prevent decay. Asking the treater to increase that retention 

based on the “more is better” theory needlessly increases the 

amount of leachable chemical in the wood without providing 

a durability benefit. It is rarely good practice to ask for a 

retention higher than those specified in wood treatment standards. A summary of appropriate retentions for various preservatives in common applications is given in Appendix B. 

Retreatment 

A similar concern arises with the practice of retreatment of 

charges that have failed to meet penetration or retention 

requirements. Although retreatment of failed charges is 

sometimes allowed in AWPA standards, it can lead to increased bleeding or leaching of preservative. Retreated material should not be used in projects in sensitive environments. 

If retreated material must be used, an additional inspection 

should be conducted to select only those pieces that meet the 

specification. 

Surface Residues 

Clean surfaces should be specified for the treated product. 

Through plant maintenance and monitoring of treatment 

solutions, it is possible to produce treated wood without 

surface residues. This is true for all types of wood 

preservatives. Material with surface residue presents an 

unnecessary environmental and safety risk, and those members should be rejected (Fig. 3). 

Bleeding of Oil-Type Preservatives 

Oil-type preservatives, such as creosote, sometimes bleed or 

ooze to the surface of the treated wood. This problem may be 

apparent immediately after treatment, but in some cases, the 

problem does not become obvious until after the product is 

placed in service in a location where it is exposed to direct 

sunlight. The volume of preservative that oozes out of the 

wood into the environment is typically quite small, but it may 

appear much larger if it spreads on the surface of standing 

water. Wood with a visibly oily surface should not be used in 

projects in sensitive environments or in applications likely to 

involve human contact (for example, decking and hand rails). 

When wood treated with oil-type preservatives is specified, it 

should be made clear that pieces with oily surfaces will not 

be accepted. 

However, the problem of bleeding that occurs later when the 

wood is placed in service is not as easily detected. This 

problem is best addressed through the control of treatment 

processes. Processes used to reduce bleeding vary somewhat, 

depending on the type of preservative, and treaters typically 

use a combination of processes to obtain a clean surface. The 

Western Wood Preservers Institute (WWPI) has developed 

best management practices (BMPs) for the most common oiltype and waterborne preservatives. The BMPs detail specific 

treatment procedures to help minimize bleeding from creosote, pentachlorophenol, and copper-naphthenate-treated 

wood. These BMPs are available at little or no cost (WWPI 

1996). The AWPA recently adopted a more general optional 

standard titled “Guidelines for Minimizing Oil-Type Wood 

Preservative Migration” (Appendix C) that describes some of 

the practices and processes used to minimize bleeding. 

Figure 3—Wood that has been properly treated and 

conditioned will not have obvious surface residue 

like that shown here. Use of treated wood with surface 

residues unnecessarily increases risks for workers 

and the environment. 
6 

Both of these documents stress several key points: 

• Maintenance of clean facilities and working solutions 

• Avoidance of over-treatment 

• The use of post-treatment conditioning techniques such 

as final vacuum, steaming, and expansion baths 

It is important that wood be treated in accordance with these 

guidelines. Although treater compliance with these guidelines 

is not easily verifiable by the purchaser or end-user, some 

aspects, such as a final steaming period or expansion bath 

and the charge retention will appear on the charge report. 

Allowing time for proper processing 

A common complaint of treaters is that customers demand 

the treated product on very short notice. This can cause the 

treater to rush or delete processing steps that improve the 

final product. This problem is especially relevant to obtaining fixation with waterborne preservatives. 

Post-Treatment Processing: Fixation 

of Waterborne Preservatives 

The active ingredients of various waterborne wood preservatives (copper, chromium, arsenic, and zinc) are initially water 

soluble in the treating solution but become resistant to leaching when placed into the wood. This leaching resistance is a 

result of the chemical fixation reactions that occur to render 

the toxic ingredients insoluble in water. The mechanism and 

requirements for these fixation reactions differ depending on 

the type of wood preservative. Some reactions occur very 

rapidly during pressure treatment while others may take days 

or even weeks to reach completion, depending on posttreatment storage and processing conditions. If the treated 

wood is placed in service before these reactions are completed, the initial release of preservative into the environment 

may be many times greater than for wood that has been 

adequately conditioned. Concerns about inadequate fixation 

have led Canada and some European countries to develop 

standards or guidelines for fixing treated wood. The AWPA 

has recently formed several task forces to consider the development of fixation, or “leaching minimization”, standards for 

CCA-C and other wood preservatives, but there are not yet 

nationally recognized standards for fixation of waterborne 

preservatives in the United States. As for the oil-type preservatives, the WWPI has taken the first steps in this direction with development of BMPs. Although it is important to 

specify that the bulk of fixation be completed before the 

treated wood is placed in service, the lack of standards in this 

area makes such specification difficult, and it is incumbent 

on the specifier to have a basic understanding of fixation 

mechanisms. 

CCA-C Fixation 

Because CCA-C is so widely used, it is the preservative for 

which we have the greatest understanding of the fixation 

process. The essence of CCA-C fixation is the reduction of 

chromium from the hexavalent to the trivalent state and the 

subsequent precipitation or adsorption of chromium, copper, 

and arsenic complexes in the wood substrate. Some of these 

reactions, such as the adsorption of copper and chromium 

onto wood components, occur within minutes or hours, while 

others are completed during the ensuing days or weeks. The 

length of time needed for fixation depends greatly on temperature, and the reactions may proceed slowly when the 

treated wood is stored outdoors in cool weather (Table 1). 

Also, increasing amounts of time are required to gain additional degrees of fixation as the process proceeds. For example, approximately 43 hours are required to progress from 

90% to 95% fixation at 21°C (70°F), but an additional 

100 hours are required to progress from 95% to 99% fixation. Because fixation at ambient temperatures may take an 

unacceptable amount of time, several techniques are used or 

have been proposed to elevate the wood temperature and 

accelerate fixation, including various forms of kiln drying, 

hot water baths, and steaming. These accelerated fixation 

methods appear to be quite effective, although care must be 

taken not to dry the wood too quickly or to elevate the temperature too much, both of which may harm the mechanical 

properties of the wood. To prevent harm to the wood, the 

AWPA has developed time–temperature limitations for posttreatment fixation of wood treated with waterborne preservatives (Table 2). Drying is not a prerequisite for achieving 

fixation in CCA-treated wood. 

There is a standard method for evaluating the completeness 

of CCA-C fixation, commonly called the chromotropic acid 

test (AWPA Method A3, Section 11 (AWPA 2000)). This 

method is outlined in Appendix D. The method involves 

removing an increment core from the treated wood and applying an indicator solution. The core turns a pinkish color if 

hexavalent chromium is present, which means the wood fails 

the test because the fixation process is not complete. This test 

is not yet routinely used within the treating industry, and 

AWPA standards do not require its use for any commodity. 

However, it is referenced in the BMPs developed by the 

WWPI as a test method for assessing fixation. Instructions 

for the use of this method in the inspection of poles have 

recently been included in AWPA standards (AWPA Standard 

M2, Part A, Section 4.5 (AWPA 2000)) and are shown in 

Appendix D. These inspection instructions would also be 

directly applicable to piling. Although further efforts are 

underway to develop more quantitative tests, the chromotropic acid method appears to be an effective and conservative means of determining whether fixation is complete in 

CCA-treated wood. 
7 

Another means of ensuring fixation of CCA-treated wood is 

through covered storage at the construction site. Once delivered, the lumber can be wrapped in tarps and stored for the 

time necessary, depending on the temperature, as shown in 

Table 1. Preferably this storage would occur well away from 

a sensitive environment. 

Fixation in Ammoniacal Preservatives 

(ACZA, ACQ-B, CC) 

Fixation in ammoniacal wood preservatives is not as well 

understood as that of CCA-C because they are less widely 

used than CCA-C. In ammoniacal preservatives, the metals 

are solubilized by ammonia and become insoluble as the 

ammonia evaporates. Some of the metals appear to simply 

precipitate within the wood, while others react with the wood 

structure. Volatilization of ammonia appears to be a key 

factor in fixation with ammoniacal preservatives, and this can 

be accomplished through either air drying or kiln drying, or a 

combination of the two. The use of stickers between layers of 

wood greatly increases the rate of drying of the treated wood. 

The WWPI’s BMPs for ACZA specify that the treated wood 

either be air dried for 3 weeks at a temperature above 16°C 

(60°F) or kiln dried to below 30% moisture content. The airdrying time may be shortened if an in retort ammonia removal process is used (WWPI 1996). Similar practices 

would be suitable for ACQ-B and CC. Unfortunately, it is 

difficult to verify that these practices have been followed, 

because there are not yet any standardized tests or methods 

for assessing the degree of fixation. As with CCA-C, fixation 

can also occur after the lumber has been delivered to the job 

site. For the ammoniacal preservatives, fixation can best be 

achieved by stickering the material and placing it in an area 

with good air flow. Although the wood should be covered to 

protect it from precipitation, it should not be covered in a 

way that impedes air circulation until after it has dried. 

Fixation in Amine Preservatives (ACQ-D, CBA-A) 

The fixation processes of the amine wood preservatives are 

poorly understood. The bulk of fixation appears to occur 

very rapidly, within a few hours after treatment. There are 

currently no standards, guidelines, or tests to ensure fixation 

in these preservatives. It is probable that air or kiln drying of 

the treated wood will ensure fixation, but such drying may 

not be necessary. Efforts are currently underway within the 

AWPA to develop tests for fixation of wood treated with 

amine preservatives. 

Fixation of CDDC 

CDDC differs from the other systems in that it is a two-stage 

treatment and the fixation product is known. A copper compound and a sodium compound are reacted within the wood 

to form an insoluble chelate. These reactions proceed rapidly, and the wood is likely to be fully fixed within hours 

of treatment. As with the amine preservatives, there are 

currently no standards or guidelines to assess fixation in 

Table 1—The approximate time needed to 

achieve fixation in CCA-treated wood as a 

function of temperaturea

Wood 

temperature Hours to percentage fixation 

 °F °C 90% 95% 99% 

<32 <0 —b —b

 —b

35 2 1,071 1,394 2,143 

40 4 789 1,027 1,578 

45 7 585 761 1,170 

50 10 436 567 872 

55 13 327 425 654 

60 16 246 321 493 

65 18 187 243 373 

70 21 142 185 285 

75 24 109 142 218 

80 27 84 109 168 

85 29 65 84 130 

90 32 50 66 101 

95 35 39 51 79 

100 38 31 40 62 

105 41 24 32 49 

110 43 19 25 38 

115 46 15 20 30 

120 49 12 16 24 

125 52 10 13 19 

130 54 7.8 10 16 

135 57 6.3 8.2 13 

140 60 5.1 6.6 10 

145 63 4.1 5.4 8.3 

150 66 3.4 4.4 6.7 

155 68 2.8 3.6 5.5 

160c

 71c 2.3 2.9 4.5 

165 74 1.9 2.4 3.7 

170 77 1.5 2.0 3.1 

175 79 1.3 1.6 2.5 

180 82 1.1 1.4 2.1 

185 85 0.9 1.1 1.8 

190 88 0.7 1.0 1.5 

195 91 0.6 0.8 1.2 

200 93 0.5 0.7 1.0 

205 96 0.4 0.6 0.9 

210 99 0.4 0.5 0.7 

215 102 0.3 0.4 0.6 

220d

 104d 0.3 0.3 0.5 

a

Calculated using the model reported by 

 Chen (1994). 

b

No fixation occurs. 

c

Maximum allowable temperature for kiln-drying 

 of CCA-treated wood. 

d

Maximum allowable temperature for steaming 

 or water immersion of CCA-treated wood. 
8 

CDDC-treated wood, but it is highly likely that fixation has 

occurred before the wood leaves the treating plant. 

Construction Practices 

On-Site Storage of Treated Wood 

Treated material that is shipped to the job site should be 

stored in an area free from standing water or wet soil. Ideally, 

it should be above ground on skids or support timbers and 

covered until used (Fig. 4). If the wood was treated with an 

ammoniacal preservative such as ACZA, ACQ-B, or CC and 

still has a noticeable odor, it can be restacked with stickers 

between the layers to aid in volatilization of the ammonia. In 

construction of wetland boardwalks, it may be most convenient to divide the material and store smaller quantities at 

intervals along the intended path of construction. In this case, 

it is desirable to place untreated bunks into the wetland and 

then place the treated material on these bunks. Again, the 

stacks of treated wood should be covered to protect them 

from precipitation. 

Minimizing Effects of 

Construction Debris 

As discussed previously, the amount of field fabrication of 

treated wood should be minimized by careful prefabrication 

before treatment. Unfortunately, this is not always practical, 

and some degree of field fabrication is usually necessary 

during construction. 

Importance of Collecting Construction Debris 

If treated wood sawdust and shavings generated during construction are allowed to enter the water below a treated wood 

structure, they make a disproportionately large contribution 

to the overall releases from that structure. Because of their 

greater surface area to volume ratio, release from small wood 

particles such as sawdust is greater than from the treated 

wood itself. A recent study developed leaching rate data for 

construction debris immersed in water and compared that to 

the release rate from CCA-treated solid wood (Lebow and 

others 2000). The amounts of copper, chromium, and arsenic 

released per gram of sawdust or drill shavings were many 

times higher than the amounts released per gram of solid 

wood. The effect was greatest for copper, where the average 

release was initially more than 20 times greater from the 

particles than from the solid wood (Fig. 5). 

The disproportionate leaching from the construction waste is 

even greater if one considers that the vast majority of treated 

wood used in construction is not immersed in water; it is 

used above the water in applications such as decking. Thus, it 

is meaningful to compare the rate of release from decking 

exposed to leaching by rainfall to that from construction 

debris that has been allowed to fall into standing water below 

the structure. A comparison of this type is shown in Figure 6. 

This comparison shows that releases of copper, chromium, 

and arsenic from construction debris discharged into standing 

water may be more than 30 to 100 times greater than releases 

from CCA-treated decking supported above the water. 

However, despite the much higher release rates from construction debris, they should not be a major concern if reasonable efforts are made to collect them. Because of their 

much smaller volume compared with the entire structure, the 

release from a few isolated chips or shavings that escape 

collection is not likely to significantly increase the overall 

release from the structure. The key is to minimize the need 

for field fabrication through prefabrication and then to collect the bulk of construction waste generated at the site. 

Methods of Containing Construction Debris 

There are many approaches to ensuring that the debris from 

field fabrication is not discharged into the environment. A 

few of the most common are discussed here, but the choice of 

a method depends on the situation and the construction crew. 

Ideally, fabrication should be done before the member is 

placed over water (Fig. 7). Tarps are commonly used to 

contain construction debris in a variety of ways. The large 

surface area of tarps makes them ideal for collecting sawdust 

from circular saws and chainsaws. Often a single cutting 

station is set up over a large tarp, and pieces to be cut or 

drilled are carried to the tarp for fabrication. If the member to 

be cut is already incorporated into the structure and cannot 

Table 2—Time–temperature limitations for posttreatment accelerated fixation of wood poles treated 

with waterborne wood preservativesa 

Limitations for steaming and hot water baths 

(maximum allowable temperature 104°C (220°F))b 

Temperature (°C (°F)) Time (h) 

105 (220) 6 

95 (203) 9 

85 (185) 12 

75 (167) 18 

65 (149) 24 

a

They are also generally applicable to piling and lumber. 

 The purpose of these limitations is to prevent harm to 

 the mechanical properties of the wood. Adapted from 

 Standard C4, American Wood-Preservers’ Association 

 Standards (AWPA 2000). 

b

There are no time–temperature limitations for kiln- and 

 air-drying (maximum allowable temperature 71°C 

 (160°F); maximum wet-bulb depression 10°C (20°F)). 
9 

 

be removed, tarps may be spread under that part of the 

structure before cutting (Fig. 8). The use of tarps to contain 

sawdust becomes more difficult under windy or rainy conditions. Shavings from drilling holes are generally easier to 

contain in a small area than is sawdust. Plastic tubs are useful 

collection devices when drilling holes on-site (Fig. 9). 

Regardless of the method used, it is inevitable that collection 

of construction debris will add some time and expense to a 

construction project. The importance of collection should be 

stressed in planning and budgeting for the project so that the 

construction crew clearly understands that debris collection

is an integral part of the construction process.

Field Preservative Treatments 

of Cuts and Bore Holes 

It is important that any untreated wood that is exposed during 

field fabrication should be treated to prevent decay. However, like the treated wood itself, these field treatment preservatives contain ingredients that could be toxic to aquatic 

organisms if they are released into the environment in sufficiently high concentrations. And, these field treatment preservatives may not be fixed or bonded to the wood in the 

same manner as the original pressure treatment. The most 

commonly used field treatment preservatives contain copper 

naphthenate, usually at a concentration of 2% copper. A 

recent study reported that the proportional release of copper 

from the copper naphthenate coating on deck boards was 

approximately 20 times greater than that for the copper from 

the CCA-C pressure treatment (Lebow and Evans 1999).

Accordingly, field treatment preservatives should be applied 

sparingly, and with care, to avoid spillage. The use of field 

treatment preservatives is best limited through prefabrication 

of the wood, which reduces the need for field cutting and 

drilling. When field treatment is needed, care in application 

of the preservative should be stressed. Whenever possible, 

the field treatment should be applied to the member before it 

is placed in a structure over water. Excess preservative 

should be wiped from the wood. If the preservative must be 

applied to wood above water, a tray, bucket, pan, or other 

collection device should be used to contain spills and drips. 

Field treatments should not be applied in the rain to wood 

that is above water. Materials treated with field preservatives 

should not be placed directly into water unless the treated 

surface is dry and free of excess preservative. AWPA Standard M4, Standard for the Care of Preservative-Treated 

Wood Products (AWPA 2000), gives requirements for field 

treatment and should be specified for construction projects in 

or over aquatic environments. 

Figure 4—Treated lumber delivered for construction projects should be supported off the ground and covered. 

Figure 5—A comparison of the rate of copper leaching 

from CCA-treated solid wood with that from three types of 

construction residue. Samples were submerged in water. 

Figure 6—A comparison of the amount of preservative 

released from solid wood or construction residue 

submerged in water with that released from decking 

exposed to rainfall. 

Total days of leaching

1 

10 

100 

1,000 

Copper release

(μg/day/g of wood)

0 10 20 30 40 

Solid wood

Chain saw

Spade bit

Circular saw

50 

Solid wood

Chain saw

Spade bit

Circular saw

0

50

100

150

200 

250 

Total release, 28 days

(μg/g of wood)

Copper Chromium Arsenic

CCA-C element

21

8

21

230

108

162

138

106

149

164

120

162

4 1 3

Chain saw dust Spade bit

shavings Circular saw dust Decking (rainfall)

Solid wood

0

50

100

150

200 

250 

Total release, 28 days

(μg/g of wood)

Copper Chromium Arsenic

CCA-C element

21

8

21

230

108

162

138

106

149

164

120

162

4 1 3

Chain saw dust Spade bit

shavings Circular saw dust Decking (rainfall)

Solid wood
10 

Use of Absorbent Materials 

With Oil-Type Preservatives 

Even wood properly treated with oil-type preservatives may 

create an oily sheen when it initially contacts standing water. 

This oily sheen can be contained and collected by floating an 

absorbent boom around or downstream from the structure. 

An absorbent boom will also help to contain any accidental 

spillage of field-treatment preservative during construction. It 

is also good practice to have absorbent pads on hand at the 

construction site in case some of the members were not 

adequately conditioned and do begin to ooze or bleed preservative. Any absorbent materials that have been used for 

collection of preservative must be disposed of using appropriate procedures. 

Water Repellants and Stains 

Wood treated with waterborne preservatives may also be 

treated with stains to enhance its appearance or with a water 

repellant to improve dimensional stability. Water repellants 

help to prevent splitting, warping, and twisting of the treated 

wood, especially of horizontal members such as decking. 

Water repellants and stains are sometimes incorporated into 

the treatment process or may be hand-applied at the construction site. These secondary treatments appear to be beneficial 

for both increasing longevity and reducing leaching from 

the treated wood, but as discussed before, field application 

of finishes must be done with great care in sensitive 

environments. 

Factory-Applied Water Repellants 

and Stains 

Several manufacturers of CCA-C and the manufacturer of 

ACQ-D offer formulations incorporating a water repellant 

into the treating solution. This allows the water repellant to 

be pressure treated into the wood more deeply than would be 

possible by hand application. It is also likely that the water 

repellant reduces leaching of preservative out of the wood 

because it slows movement of water into and out of the 

wood. CCA-treated wood may also be manufactured with a 

prestain applied to change the color and improve the appearance of the wood. At least one of these products has been 

shown to have the potential for reducing subsequent leaching 

of arsenic from CCA-treated decking (Lebow and Evans 

1999). 

Field-Applied Water Repellants 

and Stains 

Stains and water repellants are commonly brushed, rolled, or 

sprayed onto the surface of treated wood after construction. 

In addition to improvements in appearance and longevity, 

surface-applied water-repellant treatments can reduce subsequent leaching from the treated wood. One study found that 

Figure 7—These bridge components are being bored 

and field treated off-site before being positioned over 

the water. 

Figure 8—Tarps can be used to contain and collect 

sawdust generated during on-site fabrication. 

Figure 9—Plastic tubs are useful for collecting 

shavings when boring holes on-site. 
11 

leaching of copper, chromium, and arsenic from CCA-treated 

fence boards was reduced by more than 50% when a commercial water-repellant finish was brushed onto the wood 

(Cooper and Ung 1997). However, these surface treatments 

need to be reapplied annually or biannually for continued 

water-repellant protection. This requires that they be applied 

to the in-service structure, directly over aquatic or other 

sensitive environments. Because it is very difficult to apply 

these finishes without dripping or spillage into the environment below the structure, these hand-applied finishes are not 

recommended for treated wood used in sensitive applications. It is possible to apply an initial application to members, 

in a protected area, before they are installed in the structure. 

Cleaning 

Only mild cleaning techniques should be used for treated 

structures in aquatic environments. Commercial deck cleaners and brighteners should not be used because they contain 

ingredients that may be directly harmful to aquatic life and 

they have the potential for increasing the release of preservative components. Aggressive scrubbing, power-washing, or 

sanding should also be avoided since particles of treated 

wood will be removed from the surface and washed into the 

water below the structure. 

Summary 

Although treated wood does contain chemicals that are potentially toxic, studies indicate that there are no measurable 

impacts on aquatic organisms if the wood is properly treated 

and installed. The potential environmental impact of treated 

wood can be minimized by specifying that the wood be 

treated using methods that ensure chemical fixation and 

prevent the formation of surface residues or bleeding of 

preservative. Guidance to specifying such treating practices 

are offered in this document and in sources such as the Best 

Management Practices developed by the Western Wood 

Preservers Institute. In addition, responsible construction 

practices such as fabrication of the wood before treatment, 

storage of treated wood under cover, and containment and 

collection of construction residue can further reduce the 

possibility of negative environmental impacts. As with any 

other construction material, careful specification and responsible use of treated wood will optimize its performance. 

References 

AWPA. 2000. Book of standards. Granbury, TX: American 

Wood-Preservers’ Association. 

Brooks, K.M. 2000. Assessment of the environmental effects associated with wooden bridges preserved with creosote, pentachlorophenol, or chromated copper-arsenate. 

Res. Pap. FPL–RP–587. Madison, WI: U.S. Department of 

Agriculture Forest Service, Forest Products Laboratory. 

100 p. 

Chen, J. 1994. The relationship between wood temperature 

and fixation rate of CCA-C treated red pine sapwood. Toronto, Canada: University of Toronto, Faculty of Forestry. 

M.S. thesis. 

Comfort, M. 1993. Environmental and occupational health 

aspects of using CCA treated timber for walking track construction in the Tasmanian Wilderness World Heritage Area. 

Scientific Rep. 93/1. Hobart, Tasmania: Tasmanian Parks 

and Wildlife Service. 

Cooper, P.A.; Ung, Y.T. 1997. Effect of water repellents on 

leaching of CCA from treated fence and deck units—An 

update. IRG/WP 97–50086. Stockholm, Sweden: 

International Research Group. 

Forest Products Laboratory. 1999. Wood handbook—

Wood as an engineering material. Gen. Tech. Rep. FPL–

GTR–113. Madison, WI: U.S. Department of Agriculture, 

Forest Service, Forest Products Laboratory. 463 p.

Forest Products Laboratory. 2000. Environmental impact 

of preservative-treated wood in a wetland boardwalk. Res. 

Pap. FPL–RP–582. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 126 p. 

Goyette, D.; Brooks, K.M. 1998. Creosote evaluation: 

phase II. Sooke Basin study—baseline to 535 days post 

construction, 1995-1996. Report PR98–04. North Vancouver, British Columbia, Canada: Environment Canada. 568 p. 

Lebow, S.T.; Halverson, S.A.; Morrell, J.J.; Simonsen, J.

2000. Role of construction debris in release of copper, chromium, and arsenic from treated wood structures. Res. Pap. 

FPL–RP–584. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 6 p. 

Lebow, S.T.; Evans, J.W. 1999. Effect of prestain on the 

release rate of copper, chromium, and arsenic from western 

hemlock. Res. Note FPL-RN-0271. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products 

Laboratory. 6 p. 

Stilwell, D.E.; Gorny, K.D. 1997. Contamination of soil 

with copper, chromium and arsenic under decks built from 

pressure treated wood. Bulletin of Environmental 

Contamination and Toxicology. 58: 22–29. 

WWPI. 1996. Best management practices for the use of 

treated wood in aquatic environments. Vancouver, WA: 

Western Wood Preservers Institute. 35 p. 
12 

Appendix A—Prior Research 

on Environmental Impacts 

In one of the prior studies on this subject (Comfort 1993), 

chromium, copper, and arsenic levels were measured adjacent to CCA-treated boardwalks at several sites in southern 

Tasmania. At each site, three soil samples were taken within 

150 mm of the boardwalk and three reference samples were 

removed several meters from the boardwalk. The boardwalks 

at the sites varied from 1 to 14 years in age; the preservative 

retention and treating solution formulation were not reported. 

Levels of copper and chromium adjacent to the boardwalks 

were significantly elevated in comparison to the control 

samples but not to extreme levels. Arsenic levels were not 

found to be significantly elevated above the controls. The 

highest copper level detected was 49 ppm (controls were 

between 1 and 3 ppm for that site), while the highest chromium level detected was 88 ppm, approximately 60 ppm 

above the reference sample. There did not appear to be any 

relationship between the age of the boardwalk and the levels 

detected; the highest copper levels were detected around a 1-

year-old structure, while the highest chromium levels were 

detected around the 14-year-old structure (Comfort 1993). 

In a recent study that is also applicable to boardwalk decking, investigators collected soil samples from beneath residential decks constructed from CCA-treated wood (Stilwell 

and Gorny 1997). Substantially higher levels of CCA-C 

components were detected than in the Tasmanian study. 

Several samples from under decks contained more than 

100 ppm copper, and a maximum level of 410 ppm copper 

was detected under one of the decks. Chromium concentrations in some samples from under the decks were also more 

than 100 ppm, and maximum arsenic concentrations of 200 

to 300 ppm were reported. Overall, the average copper, 

chromium, and arsenic levels detected under the decks were 

75, 43, and 76 ppm, respectively, while those in nearby 

control areas were 17, 20, and 4 ppm, respectively (Stilwell 

and Gorny 1997). The authors also noted that the concentration of CCA components in the soil decreased rapidly with 

soil depth. In contrast to the Tasmanian study, Stilwell and 

Gorny did note an increase in CCA component levels with 

increasing age of the deck (Stilwell and Gorny 1997). 

Neither of these studies evaluated releases in aquatic environments, or the resulting environmental impact, but two 

other recently initiated projects are addressing these questions. In one project, the Forest Service, the Bureau of Land 

Management, and industry partners cooperated to conduct a 

study of the leaching and environmental impacts of waterborne preservatives from wood used in construction of a 

wetland boardwalk (Forest Products Laboratory 2000). The 

construction project was considered “worst case” because the 

site had high rainfall and large volumes of treated wood were 

used. Separate boardwalk test sections were constructed 

using untreated wood and wood treated with ACQ-B, ACZA, 

CCA-C, or CDDC. Surface soil, sediment, and water samples 

were removed before construction and at intervals after 

construction to determine the concentrations and movement 

of leached preservative elements. Aquatic insect populations 

in the vegetation, in sediments, and on artificial substrates 

were also monitored and related to environmental concentrations of leached wood preservative components. During the 

first year, each of the preservatives evaluated released measurable amounts of copper, chromium, zinc, or arsenic into 

rainwater collected from the wood. Each preservative also 

appeared to elevate levels of respective preservative components in the soil or sediment adjacent to the treated wood to 

varying degrees. In some cases, levels appeared to peak soon 

after construction, while in other cases, levels appeared to 

increase during the course of the year. With few exceptions, 

elevated environmental concentrations of preservative components were confined to within close proximity to the 

boardwalk. These levels of environmental accumulation did 

not appear to have any measurable biological impact. Although seasonal fluctuations in insect populations were 

noted, none of the invertebrate taxa evaluated were significantly reduced in number in the wetlands surrounding any of 

the types of treated wood. 

Following the wetland boardwalk study, Brooks (2000) 

evaluated the environmental effects of timber bridges treated 

with either CCA-C, pentachlorophenol, or creosote. In that 

study, bridges that had been in service for several years were 

evaluated by comparing upstream and downstream levels of 

preservative concentrations in sediments to populations of 

aquatic insects at the same sampling locations. The two 

pentachlorophenol-treated bridges evaluated by Brooks 

(2000) were located in forested areas in the states of Washington and Oregon. The Washington site appeared to contain 

low levels of pentachlorophenol, although the concentrations 

detected were approaching the lower detection limit of the 

instrumentation. No biological effects would be expected at 

those levels, and none were detected in association with this 

bridge. At the pentachlorophenol-treated bridge in Oregon, 

four sediment samples were collected from under the bridge 

or 0.9 m (3 ft) downstream from the bridge. These samples 

also contained slightly elevated levels of pentachlorophenol. 

A small decrease in several biological indices were also 

noted directly under the bridge, but this appeared to be 

related to differences in stream bottom habitat in comparison 

to the upstream control. No adverse effects were noted when 

a bioassay was conducted on sediments removed from under 

the bridge (Brooks 2000). 

Two CCA-treated bridges in Florida were also evaluated, one 

over a saline bay and the other over a freshwater marsh 

(Brooks 2000). The bridge over the bay was in the final 

stages of construction, and the bridge over the marsh had 

been constructed 2 years earlier. Some samples of sediments 

removed within 3 m (10 ft) of the newly constructed bridge 

did contain elevated levels of copper, chromium, and arsenic. 
13 

The patchy nature of the elevated samples and the observation of wood chips in the sediments led Brooks to suspect 

that at least a portion of the elevated samples contained 

treated wood sawdust. Despite the elevated levels of CCA 

detected in the sediments, no adverse biological effects were 

observed. Very slightly elevated copper, chromium, and 

arsenic levels were also noted in sediments within 3 to 6 m 

(10 to 20 ft) of the 2-year-old bridge, but again, no adverse 

biological effects were observed. In this case, the population 

and diversity of aquatic insects actually appeared to increase 

with proximity to the bridge. 

Brooks also evaluated two creosote-treated bridges located in 

agricultural areas in Indiana; one had been in service for 

approximately 2 years and the other for approximately 17 

years. In each case, elevated levels of PAH were detected in 

sediments 1.8 to 3 m (6 to 10 ft) downstream from the 

bridges, and these levels approached levels of concern for the 

newer bridge. However, no significant effect on insect populations was noted downstream from the newer bridge. 

 

There did appear to be a reduction in the population and 

diversity of aquatic insects within 6 m (20 ft) downstream 

from the older creosote-treated bridge, but the author postulates that this trend was caused by the deposition of maple 

leaves in this area and was not a response to released PAH 

(Brooks 2000). This hypothesis is supported by the fact that 

sediments removed from that area did not adversely affect 

aquatic invertebrates in a laboratory bioassay. 

The release and biological impacts of creosote have also 

been evaluated for newly installed six-piling dolphins installed in the waters of Sooke Basin on Vancouver Island, 

British Columbia, Canada (Goyette and Brooks 1998). PAH 

contamination was detected within 7.5 m (25 ft) downstream 

from the piling, and significant biological effects were noted 

within 0.65 m (2.1 ft) of the perimeter of the structure. Slight 

biological effects were noted in laboratory bioassays of 

sediments removed from up to 2.0 m (6.6 ft) downstream 

from the piles but not in the infaunal community (Goyette 

and Brooks 1998). 
14 

Appendix B—Preservative Retention Levels 

Creosote, oilborne, and waterborne preservatives and retention levels for various wood productsa

 Creosote and oilborne preservative retention (kg/m3 (lb/ft3)) 

Form of product and 

service condition Creosote 

Creosote 

solutions 

Creosotepetroleum 

Pentachloro- 

 phenol, P9, 

 Type A 

Pentachloro- 

 phenol, P9, 

 Type E 

 Copper 

naphthenate 

Oxine 

copper 

AWPA 

standard 

A. Ties (crossties and switch 

ties) 

96–128 

(6–8) 

112–128 

(7–8) 

112–128 

(7–8) 

5.6–6.4 

(0.35–0.4) 

NRb

 NR NR C2/C6 

B. Lumber, timber, plywood; 

bridge and mine ties

 

(1) Salt waterc

 400 (25) 400 (25) NR NR NR NR NR C2/C9 

(2) Soil and fresh water 160 (10) 160 (10) 160 (10) 8 (0.50) NR 0.96 (0.06) NR C2/C9 

(3) Above ground 128 (8) 128 (8) 128 (8) 6.41 (0.40) 6.4 (0.40) 0.64 (0.04) 0.32 (0.02) C2/C9 

C. Piles 

(1) Salt waterc

 C3/C14/C18 

Borer hazard, 

moderate 

320 (20) 320 (20) NR NR NR NR NR 

Borer hazard, severe NR NR NR NR NR NR NR 

Dual treatment 320 (20) 320 (20) NR NR NR NR NR 

(2) Soil, fresh water, or 

foundation 

96–272 

(6–17) 

96–272 

(6–17) 

96–272 

(6–17) 

4.8–13.6 

(0.30–0.85) 

NR 1.60 (0.10) NR C3/C14/C24 

D. Poles (length >5 m (>16 ft)) 

(1) Utility 120–256 

(7.5–16) 

120–256 

(7.5–16) 

120–256 

(7.5–16) 

4.8–12.8 

(0.30–0.80) 

NR 1.2–2.4 

(0.075–0.15) 

NR C4 

(2) Building, round and 

sawn 

144–216 

(9–13.5) 

NR NR 7.2–10.9 

(0.45–0.68) 

NR NR NR C4/C23/C24 

(3) Agricultural, round 

and sawn 

120–256 

(7.5–16) 

120–256 

(7.5–16) 

NR, round 

(sawn, 192 

(12)) 

6.1–9.6 

(0.38–0.60) 

NR NR, round 

(sawn, 

1.2 (0.075)) 

NR C4/C16 

E. Posts (length <5 m (<16 ft)) 

(1) Agricultural, round 

and sawn, fence 

128–160 

(8–10) 

128–160 

(8–10) 

128–160 

(8–10) 

6.4–8.0 

(0.40–0.50) 

NR sawn, 0.96 

(0.060) 

round, 

0.88 (0.055) 

C2/C5/C16 

(2) Commercial–

residential construction, round and sawn 

128–192 

(8–12) 

128–192 

(8–12) 

128–192 

(8–12) 

8–9.6 

(0.50–0.60) 

NR NR NR C2/C5/C15/C23 

(3) Highway construction 

Fence, guide, sign, 

and sight 

128–160 

(8–10) 

128–160 

(8–10) 

128–160 

(8–10) 

6.4–8.1 

(0.40–0.50) 

NR sawn four 

sides, 0.96 

(0.06) 

NR C2/C5/C14 

Guardrail and spacer 

blocks 

160–192 

(10–12) 

160–192 

(10–12) 

160–192 

(10–12) 

8–9.6 

(0.50–0.60) 

NR sawn four 

sides, 1.2 

(0.075) 

NR C2/C5/C14 

F. Glued-laminated 

timbers/laminates 

 

(1) Soil and fresh water 160 (10) 160 (10) 160 (10) 9.6 (0.60) NR 9.6 (0.60) NR C28 

(2) Above ground 128 (8) 128 (8) 128 (8) 4.8 (0.30) NR 6.4 (0.40) 3.2 (0.20) C28 

a

From table 14–2 in Forest Products Laboratory (1999). Retention levels are those included in Federal Specification TT–W–571 and Commodity 

 Standards of the American Wood-Preservers’ Association. Refer to the current issues of these specifications for up-to-date recommendations and 

 other details. In many cases, the retention is different depending on species and assay zone. Retentions for lumber, timber, plywood, piles, poles, 

 and fence posts are determined by assay of borings of a number and location as specified in Federal Specification TT–W–571 or in the Standards of 

 the American Wood-Preservers’ Association referenced in last column. Unless noted, all waterborne preservative retention levels are specified on 

 an oxide basis. 
15 

 

 Waterborne preservative retention (kg/m3

 (lb/ft3)) 

ACC 

ACZA 

or ACA 

CCA

Types I, II, or III 

ACQ 

Type B 

ACQ 

Type D 

CDDC 

as Cu CC 

CBA 

Type A AWPA standard 

 NR NR NR NR NR NR NR NR C2/C6 

 

 NR 40 (2.50) 40 (2.50) NR NR NR 40 (2.50) NR C2/C9 

 6.4 (0.40) 6.4 (0.40) 6.4 (0.40) 6.4 (0.40) 6.4 (0.40) 3.2 (0.20) 6.4 (0.40) NR C2/C9 

 4.0 (0.25) 4.0 (0.25) 4.0 (0.25) 4.0 (0.25) 4.0 (0.25) 1.6 (0.10) 4.0 (0.25) 3.27 (0.20) C2/C9 

 

 C3/C14/C18 

NR 24 (1.5) 24.1 (1.5) NR NR NR NR NR 

 NR 40 (2.50) 40 (2.50) NR NR NR NR NR 

 NR 16 (1.00) 16 (1.00) NR NR NR NR NR 

NR 12–16 

(0.80–1.0) 

12–16 

(0.80–1.0) 

NR NR NR NR NR C3/C14/C24 

 

 NR 9.6 (0.60) 9.6 (0.60) 9.6 (0.60) NR NR NR NR C4 

NR 9.6–12.8 

(0.60–0.80) 

9.6–12.8 

(0.60–0.80) 

9.6 (0.60) 9.6 (0.60) 3.2 (0.2) NR NR C4/C23/C24 

NR 9.6 (0.60) 9.6 (0.60) 9.6 (0.60) NR NR NR NR C4/C16 

 

NR 6.4 (0.40) 6.4 (0.40) 6.4 (0.40) NR NR NR NR C2/C5/C16 

8 (0.50), (NR, 

sawn structural 

members) 

6.4–9.6 

(0.40–0.60) 

6.4–9.6 

(0.40–0.60) 

6.4–9.6 

(0.40–0.60) 

6.4–9.6 

(0.40–0.6) 

3.2 (0.20) 6.4 (0.4), (NR, 

sawn structural 

members) 

NR C2/C5/C15/C23 

 

8–9.9 

(0.50–0.62) 

6.4 (0.40) 6.4 (0.40) 6.4 (0.40) NR NR NR NR C2/C5/C14 

NR 8 (0.50) 8 (0.50) 8 (0.50) NR NR NR NR C2/C5/C14 

 

8 (0.50)d

 6.4 (0.40)d 6.4 (0.40)d NR NR NR NR NR C28 

3.2 (0.20) 4 (0.25) 4 (0.25) NR NR NR NR NR C28 

b

NR, not recommended. 

c

Dual treatments are recommended when marine borer activity is known to be high (see AWPA C2, C3, C14, and C18 for details). 

d

For use when laminations are treated prior to bonding. 
16 

Appendix C—Guidelines For Minimizing 

Oil-Type Wood Preservative Migration1 

(This standard is promulgated according to a consensus procedure and is under the jurisdiction of AWPA Subcommittee P-3) 

M20-00 

1.0 Introduction 

1.1 The purpose of this protocol is to provide guidelines for minimizing environmental contamination and human exposure of 

oil-type wood preservatives contained in pressure treated wood products. This guideline will assist wood treaters in adopting 

treatment and handling procedures to reduce migration of the pre-servative from the wood and avoid shipment of treated 

product that may otherwise have a tendency to lose pre-servative from the wood surface. 

2.0 Scope 

2.1 These guidelines apply to wood products pres-sure treated with oil-type preservative systems under the jurisdiction of 

AWPA subcommittee P3. These systems include the preservatives Standard P1/P13 (creosote), Standard P2 (creosote solution),Standard P3(creosote -petroleum oil solution) and Standard P8 (oil-borne preservatives). The related standards, which 

are a part of the preservative systems listed, include Standard P4 (petroleum oil for blending with creosote) and Standard P9 

(solvents for organic preservative systems used as carrier oils for the oil-borne preservatives). 

2.2 These guidelines should be employed in con-junction with a thorough understanding of the AWPA Treatment Standards 

covering the treated wood com-modities and preservatives specified. There are substantial differences in treatment methods 

for different species of wood and preservative systems. Where these guidelines may be in conflict with specific provisions of 

the AWPA Treatment Standards, the Treatment Standards take precedence. 

2.3 This protocol should only be used after reading and thoroughly understanding the preservative product label. A guideline 

shall not be used if it contradicts a product label recommendation or if it is prohibited by the product label. 

2.4 These guidelines do not address the inherent toxicological and environmental properties of the preservatives themselves. 

These matters are under the jurisdiction of the United States Environmental Protection Agency (US EPA). 

3.0 Treatment Guidelines 

3.1. Prior to treatment all surface debris such as sawdust, wood shavings, and dirt should be removed from wood products. 

3.2 The treatment cylinder (retort) should be kept clean and free of debris. 

3.3 Work tanks should be drained and cleaned periodically to reduce the residue and solids present in the treatment solution. 

Several process techniques may be utilized to maintain a clean working solution. These processes include filtering, turnover 

of tank inventory, minimizing storage or treating tank levels, and maintaining a high quality supply source. 

3.4 Wood products should be sorted and treated by charges containing wood of similar sizes, classes, species, species groupings, moisture contents, conditioning methods, and treatability levels. 

3.5 Treating solutions should be kept as moisture-free as possible. For preservative systems employing AWPA P9 oils, any free 

water and accumulated emulsion should be drained from the work tank on a daily basis. Creosote systems should be thermally dehydrated on a regular basis to maintain the low moisture content required in the AWPA Standards. 

3.6 Most all oil-type preservative retention levels are controlled using initial air pressure in the Rueping (empty-cell with initial 

air) process. Using the lowest initial air pressure to achieve the desired results of treatment will significantly reduce the potential for excessive post-treatment preservative loss in a liquid form which remains on the wood surface, commonly called 

“bleeding.” 

3.7 Retreating a non-conforming charge with any oil-type preservative greatly increases the potential for preservative migration 

or exudation from the treated materials. Good quality control practices and treating experience will reduce retreatments and 

subsequent potential for preservative loss. 

3.8 Use an acceptable post-treatment cleaning or conditioning process to minimize potential migration of the preservative from 

the wood. Specific cycles will vary with the wood product, wood species, preservative, retention level, plant equipment and 

experience in treating a specific commodity. 

___________________ 

1

Reprinted with permission from AWPA. Copyright American Wood-Preservers’ Association, 2000. 
17 

Appendix D—Method for Determining the Presence of 

Hexavalent Chromium in Treated Wood1

Part I. Chromotropic Acid Test 

Scope 

When chromotropic acid is complexed with chromium (VI), a pink to purple color is formed. Such visible color does not occur 

with chromium (III). This method indicates, by the absence of the colored chromotropic acid complex, the presence of 15 ppm 

or less chromium (VI). 

Reagent 

Dissolve 0.5 grams of chromotropic acid (4,5-dihydroxy-2,7-naphthalene disulfonic acid) or its disodium salt in 100 ml. of 1N 

(approx. 5 wt.%) sulfuric acid. This solution should have a shelf life of at least 2 months. 

Procedure 

Borings for testing should be taken by hand, split and the bit thoroughly rinsed in water between borings. 

Borings should be allowed to come to room temperature before testing. 

Place the freshly cut boring on a white blotter paper surface, such as filter paper or a white index card. 

With a medicine dropper, apply several drops of the chromotropic acid solution to wet the core. Usually 5 to7 drops per one-inch 

length of core is sufficient for a core still wet from treatment. If the core is dry, it is helpful to apply 2 or 3 drops of the solution 

carefully and allow the surface of the core to become saturated before applying the remaining drops. Allow the reaction to continue for at least 10 minutes. Then remove the core and observe the colored complex that has leached onto the blotter; if the 

blotter is not wet, insufficient solution was applied and the test must be repeated. Any pink to purple color on the blotter indicates the incomplete conversion of chromium (VI) to chromium (III). 

Sensitivity for Color 

The minimum detection limit for the method is 15 ppm chromium (VI). 

Part II. Standard for Sampling a Charge of Poles or Piles2

M2-00 

STANDARD FOR INSPECTION OF WOOD PRODUCTS TREATED WITH PRESERVATIVES 

PART A 

POLES, PILING, TIES, TIMBERS AND OTHER COMMERCIAL/INDUSTRIAL PRODUCTS NORMALLY SUBJECT TO WRITTEN SPECIFICATIONS BY THE PURCHASER 

(This Standard is promulgated according to a consensus procedure and is under the jurisdiction of AWPA Subcommittee T-7) 

4. INSPECTION AFTER TREATMENT

4.5 Reduction of Chromium (VI). When required by the applicable AWPA Commodity Standard or by the purchaser, CCA 

treated material will be tested for completion of the chemical reduction of soluble Chromium (VI) using Method A3, 

Section 11. 

__________________________ 

1

From Standard A3, Determination of Preservatives and Fire Retardants (AWPA 2000). Reprinted with permission. Copyright 

American Wood-Preservers’ Association, 2000. 

2

From AWPA Standard for inspection of wood products treated with preservatives. Part A. Poles, piling, ties, timbers, and other 

commercial/industrial products normally subject to written specifications by the purchaser. Sec. 4, Inspection after treatment 

(AWPA, 2000). 
18 

A borer core shall be taken at a point in a plane approximately 300 – 600 mm (1 – 2 ft) below the brand of 5 poles in each 

charge. The corer bit should be thoroughly rinsed in cool water between borings to minimize contamination and reduce the 

possible influence of elevated bit temperatures on the indicated presence of hexavalent chromium. The outer 13 mm (0.5 inch) of

each core shall be evaluated for the presence of hexavalent chromium. Only cores that are fully penetrated in the outer 13 mm 

(0.5 inch) and meet the pole penetration requirements shall be evaluated. The jig used for sectioning and splitting the cores shall 

not be allowed to lie unprotected in the sun. If one (1) or fewer of the cores tests positive for the presence of hexavalent chromium, the charge shall be considered conforming. If three (3) or more cores test positive for the presence of hexavalent chromium, the charge shall be re-evaluated (see table below). If two (2) of the five (5) poles test positive for hexavalent chromium, 

the charge shall be deemed non-conforming, but the inspector may immediately remove cores from one additional set of (5) 

poles. The charge may be deemed conforming if none of the second set of poles test positive for hexavalent chromium; otherwise 

the charge shall be deemed non-conforming and shall not be sampled again until the minimum waiting period has elapsed. During each subsequent inspection of a failed charge, five (5) poles will again be sampled; these five poles shall include any poles 

that failed during prior evaluations. 

Minimum waiting period between inspections 

for the presence of hexavalent chromiuma 

Fixation 

Temperatures 

Minimum Hours 

Between Tests 

Below 20 C (68 F) 24 

20 – 35 C (68 – 95 F) 12 

35 – 50 C (95 – 122 F) 6 

50 – 65 C (122 – 149 F) 3 

Above 65 C (149 F) 1.5 

a

Originally Table 1 in standard.