Alternatives to 

Chromated Copper 

Arsenate for Residential 

Construction 

Stan Lebow 

United States

Department of 

Agriculture 

Forest Service 

Forest 

Products 

Laboratory 

Research 

Paper 

FPL−RP−618 
Abstract 

For decades chromated copper arsenate (CCA) was the 

primary preservative for treated wood used in residential 

construction. However, recent label changes submitted by 

CCA registrants will withdraw CCA from most residential 

applications. This action has increased interest in arsenicfree preservative systems that have been standardized by the 

American Wood Preserversí Association. These include acid 

copper chromate (ACC), alkaline copper quat (ACQ), copper azole (CBA-A and CA-B), copper citrate (CC), copper 

dimethyldithio-carbamate (CDDC), and copper HDO 

(CX-A). All of these CCA alternatives rely on copper as 

their primary biocide, although some have co-biocides to 

help prevent attack by copper-tolerant fungi. These alternative treatments have appearance and handling properties 

similar to those of CCA and are likely to be readily accepted 

by consumers. Prior studies indicate that these treatments 

release preservative components into the environment at a 

rate greater than or equal to that of CCA, but because their 

components have lower mammalian toxicity they are less 

likely to cause concern in residential applications. As the 

treated wood industry evolves, it is probable that a wider 

range of types and retentions of wood preservatives will 

become available, with the treatment more closely tailored 

to a specific type of construction application. 

Keywords: chromated copper arsenate (CCA), alternative 

preservatives, leaching, environmental concerns 

April 2004 

Previously published in the Proceedings of Environmental Impacts 

of Preservative-Treated Wood; February 8ñ10, 2004, Orlando, Florida. 

Lebow, Stan T. 2004. Alternatives to chromated copper arsenate for residential construction. Res. Pap. FPL-RP-618. Madison, WI: U.S. Department of 

Agriculture, Forest Service, Forest Products Laboratory. 9 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 53726ñ2398. This publication is also available online at 

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Contents 

 Page 

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

Applications Affected by CCA Label Changes .................... 1

Challenges in Developing New Wood Preservatives............ 2

Alternatives to CCA Preservative Treatment........................ 2

Acid Copper Chromate ..................................................... 2

Alkaline Copper Quat ....................................................... 3

Ammoniacal Copper Citrate ............................................. 4

Copper Azole .................................................................... 4

Copper Dimethyldithio-Carbamate................................... 4

Copper HDO (CX-A)........................................................ 4

Borates .............................................................................. 4

Practical Differences Between CCA Alternatives ............ 5

Environmental Concerns With CCA Alternatives ................ 5

Concluding Remarks............................................................. 8

Literature Cited ..................................................................... 8
Alternatives to Chromated Copper 

Arsenate for Residential Construction 

Stan T. Lebow, Research Forest Products Technologist

Forest Products Laboratory, Madison, Wisconsin 

Introduction 

Because it is biodegradable, wood used in applications 

where it may be attacked by decay fungi or insects should be 

protected by pressure treatment with wood preservatives. 

Wood preservatives are broadly classified as either water- or 

oil-based, depending on the chemical composition of the 

preservative and the carrier used during the treating process. 

The oil-type preservatives creosote, pentachlorophenol, and 

copper naphthenate are commonly used for applications such 

as posts, poles, piles, and glue-laminated beams. They are 

not usually used for applications that involve frequent contact with human skin or inside dwellings because they may 

be visually oily or oily to touch, or have a strong odor. Water-based preservatives have become more widely used in 

recent years because the treated wood has a dry, paintable 

surface and no odor. The most common of these preservatives has been chromated copper arsenate (CCA). Wood 

treated with CCA, commonly called ìgreen treatedî wood, 

dominated the residential market for several decades and 

was sold at lumberyards under a variety of trade names. 

However, as a result of voluntary label changes submitted to 

the Environmental Protection Agency (EPA) by the CCA 

registrants, the EPA labeling of CCA will limit the use of the 

product primarily to industrial applications. The label change 

was effective December 31, 2003, although suppliers have 

been allowed to sell existing stocks of CCA-treated wood 

after that date. The recent action does not affect end-uses 

of wood treated before December 31, 2003, or any existing 

structures. 

Applications Affected by 

CCA Label Changes 

The label changes cite specific commodity standards listed in 

the 2001 edition of the American Wood Preserversí Association (AWPA) standards (AWPA 2001). The changes were 

made as part of the ongoing CCA re-registration process and 

in light of current and anticipated market demand for alternative preservatives for non-industrial uses. Most applications 

of sawn lumber and timbers are affected, although CCA will 

still be allowed for treatment of roundstock (poles, building 

posts, and piles). However, there are exceptions that allow 

the use of CCA for some sawn products. Examples of sawn 

products that still may be treated with CCA include the 

following: 

• Lumber in permanent wood foundations (Fig. 1) 

• Sawn structural piles used to support residential and commercial structures 

• Sawn building poles and posts used in agricultural construction 

• Wood used in highway construction, including lumber and 

timbers 

• Utility pole crossarms 

• Wood of all dimensions used in salt water and subject to 

marine borer attack 

Treatment of engineered wood products, such as gluedlaminated beams and timbers, structural composite lumber, 

and plywood, will also be allowed in most applications. 

Overall, the label changes are expected to result in a 70% to 

80% reduction in the volume of CCA-treated wood. This 

raises the questions: What preservatives will be used to 

replace CCA? What are the characteristics of these 

alternatives? 

Figure 1óCCA is still registered for some residential 

applications, such as permanent wood foundations. 
2 

Challenges in Developing 

New Wood Preservatives

We have become accustomed to rapidly developing and 

changing products in most residential commodities. Consumers and regulators sometimes seem frustrated that the 

wood preservation community does not rapidly produce a 

wide selection of effective replacements for CCA. Unfortunately, it currently takes many years to bring a new wood 

preservative to market. A formulation must meet several 

important criteria to be an effective wood preservative. The 

first challenge is identification of a combination of active 

ingredients that will provide long-term protection against a 

wide range of organisms that damage wood. In addition to 

decay fungi, the preservative must protect against attack by 

termites, carpenter ants, beetles, and other insects. Even 

within decay fungi there is a range of species and strains that 

differ in chemical tolerance. The preservative must also 

resist detoxification by non-wood-attacking fungi and bacteria. These requirements preclude the use of compounds that 

have a very narrow or specific toxicity to only one type of 

organism. A wood preservative needs some degree of broad 

spectrum efficacy, which is in direct conflict with the goal of 

identifying environmentally friendly compounds. 

Because a wood preservative must protect against a range of 

organisms while simultaneously resisting environmental 

degradation, it has proven difficult to develop reliable methods of accelerating evaluation of preservatives. Typically, at 

least 3 to 5 years of test stake exposure in multiple locations 

is needed to demonstrate the potential for long-term efficacy 

in ground-contact applications (Fig. 2). In addition, a battery 

of tests, including laboratory fungal and leaching evaluations, corrosion tests, and mechanical property evaluations, 

are needed to list a preservative formulation within the 

AWPA Book of Standards. AWPA members, who represent 

government agencies, universities, and chemical suppliers, 

review the results of these tests. The data must then be supplemented with commercial treatment trials to demonstrate 

that the formulation can be effectively and practically applied to wood products. 

This efficacy testing and evaluation is independent of that 

needed to obtain EPA registration of a new pesticide product. Registration of a new biocidal active component may 

require several years and millions of dollars to complete. 

Because of the high cost of EPA registration of new compounds, there is a strong tendency to use compounds that 

have already been registered for other applications. 

As a result of all these factors, it is difficult to develop new 

preservatives and bring them quickly to market. The wood 

treatment industry cannot immediately respond to changing 

regulatory or societal expectations, but instead must attempt 

to anticipate and plan for future changes. 

Alternatives to CCA 

Preservative Treatment

Preservative manufactures have been working for years to 

develop arsenic-free alternatives. The AWPA has standardized several arsenic-free preservative formulations, although 

not all are available commercially. All of these alternatives 

rely on copper as their primary active ingredient because 

copper is an excellent fungicide, is relatively inexpensive, 

and has relatively low mammalian toxicity. The CCA alternatives described here are acid copper chromate, alkaline 

copper quat, ammoniacal copper citrate, copper azole, copper dimethyldithio-carbamate, copper HDO, and borates. 

Acid Copper Chromate 

Acid copper chromate (ACC) has been used sporadically as 

a wood preservative in Europe and the United States since 

the 1920s. In the last few decades, it has been primarily used 

for the treatment of wood used in cooling towers. ACC 

contains 31.8% copper oxide and 68.2% chromium trioxide 

(Table 1). The treated wood is a light greenish-brown and 

has little noticeable odor. Tests on stakes and posts exposed 

to decay and termite attack indicate that ACC provides 

acceptable average service life, but that wood used in ground 

contact may suffer occasional early failure from attack by 

copper-tolerant fungi (Lebow and others 2003). ACC is 

listed in AWPA standards for treatment of a wide range of 

softwood and hardwood species used above ground or in 

ground contact. However, in critical structural applications 

such as highway construction, its AWPA listings are limited 

to sign posts, handrails and guardrails, and glue-laminated 

beams used above ground. It may be difficult to obtain adequate penetration of ACC in some of the more refractory 

wood species such as white oak or Douglas-fir. This is because ACC must be used at relatively low treating temperatures (38oC to 66oC, 100oF to 150oF), and because rapid 

reactions of chromium in the wood can hinder further 

penetration during the longer pressure periods needed for 

refractory species. The high chromium content of ACC, 

Figure 2óWood preservative formulations undergo 

rigorous testing, including lengthy field trials. 
3

however, has the benefit of preventing much corrosion that 

might otherwise occur with an acidic copper preservative. 

To date, ACC does not have an EPA label and its future 

availability is unclear. 

Alkaline Copper Quat 

Alkaline copper quat (ACQ) has been commercially available in some parts of the United States for several years 

(Fig. 3). The active ingredients in ACQ are copper oxide 

(67%) and a quaternary ammonium compound (quat). Multiple variations of ACQ have been standardized or are in the 

process of standardization. ACQ type B (ACQ-B) is an 

ammoniacal copper formulation, ACQ type D (ACQ-D) an 

amine copper formulation, and ACQ type C (ACQ-C) a 

combined ammoniacalñamine formulation with a slightly 

different quat compound. ACQ-B treated wood has a dark 

greenish-brown color that fades to a lighter brown and may 

have a slight ammonia odor until the wood dries. Wood 

treated with ACQ-D is lighter brown and has little noticeable 

odor, while the appearance of wood treated with ACQ-C 

varies between that of wood treated with ACQ-B or ACQ-D, 

depending on the formulation. The formulations are limited 

because ACQ is the most recently standardized formulation. 

Minimum retentions of ACQ formulations are specified for 

wood used above ground and in ground contact (Table 1). 

The multiple formulations of ACQ allow some flexibility in 

achieving compatibility with a specific wood species and 

application. When ammonia is used as the carrier, ACQ has 

improved ability to penetrate into difficult-to-treat wood 

species. However, in wood species that can be readily 

treated, such as Southern Pine, an amine carrier can be used 

to provide a more uniform surface appearance. 

Table 1óPreservative formulations standardized for applications typical of residential construction 

Retention 

kg/m3 (lb/ft3

) 

Preservative formulation as 

listed in AWPA standards Proportion of preservative component 

Above 

ground 

Ground 

contact 

Acid copper chromate (ACC) 32% CuO 68% CrO3 4.0 (0.25) 6.4 (0.40) 

Alkaline copper quat (ACQ-B, D) 67% CuO 33% DDACa 4.0 (0.25) 6.4 (0.40) 

Alkaline copper quat (ACQ-C) 67% CuO 33% BACb

 4.0 (0.25) 6.4 (0.40) 

Copper azole (CA-B) 96% Cu 4% azolec

 1.7 (0.10) 3.3 (0.21) 

Copper azole (CBA-A) 49% Cu 2% azolec

 

49% H3BO3

3.3 (0.20) 6.5 (0.41) 

Copper citrate (CC) 62% CuO 38% citric acid 4.0 (0.25) 6.4 (0.40) 

Copper bis dimethyldithiocarbamate (CDDC) 17%ñ29% CuO 71%ñ83% SDDCd

 1.6 (0.10) 3.2 (0.20) 

Copper HDO (CX-A) (pending 

EPA registration) 61.5% CuO 14% CuHDOe

 

24.5% H3BO3

2.4 (0.15) NAf

a

Didecylthyl ammonium chloride. 

b

Alkylbenzyldimethyl ammonium chloride. 

c

Tebuconazole. 

d

Sodium dimethyldithio-carbamate. 

e

Bis-(N-cyclohexyl-diazenium dioxy)copper. fNot in standards as yet. 

Figure 3óACQ-treated wood has been available 

commercially for several years in some areas of the 

United States.
4 

Ammoniacal Copper Citrate 

Ammoniacal copper citrate (CC) utilizes copper oxide as a 

fungicide and insecticide and citric acid to aid in the distribution of copper within the wood structure. The color of the 

treated wood varies from light green to dark brown (Fig. 4). 

The treated wood may have a slight ammonia odor until it 

has thoroughly dried. Exposure tests with stakes and posts 

placed in ground contact indicate that the treated wood 

resists attack by both fungi and insects. However, it appears 

that the lack of a co-biocide may render wood used in 

ground contact vulnerable to attack by certain species of 

copper-tolerant fungi (Clausen and Green 2003). CC is listed 

in AWPA standards for treatment of a range of softwood 

species and wood products for wood used above ground or 

in ground contact. CC is not listed in AWPA standards for 

use in highway construction or other structurally critical 

applications. As with other preservatives containing ammonia, CC has an increased ability to penetrate into difficult-totreat wood species such as Douglas-fir. To date, CC has had 

only limited commercial availability. 

Copper Azole 

Copper azole relies primarily on amine copper, but with cobiocides, to protect wood from decay and insect attack 

(Fig. 5). The first copper azole formulation developed was 

copper azole Type A (CBA-A), which contains 49% copper, 

49% boric acid, and 2% Tebuconazole. More recently, the 

copper azole Type B (CA-B) formulation was standardized. 

CA-B does not contain boric acid and is comprised of 96% 

copper and 4% Tebuconazole. Wood treated with either 

copper azole formulation has a greenish-brown color and 

little or no odor. The formulations are listed in AWPA standards for treatment of a range of softwood species used 

above ground or in ground contact. Although listed as an 

amine formulation, copper azole may also be formulated 

with an amineñammonia solvent. The ammonia may be 

included when the copper azole formulations are used to 

treat refractory species, and the ability of such a formulation 

to adequately treat Douglas-fir has been demonstrated. The 

inclusion of ammonia, however, is likely to have slight 

effects on the surface appearance and initial odor of the 

treated wood. 

Copper Dimethyldithio-Carbamate 

Copper dimethyldithio-carbamate (CDDC) is a reaction 

product formed within the wood after treatment with two 

different treating solutions. It contains copper and sulfur 

compounds. CDDC is standardized for treatment of Southern 

Pine and some other pine species at copper retentions of 

1.6 kg/m3 (0.1 lb/ft3

) or 3.2 kg/m3 (0.2 lb/ft3) for wood used 

above ground or in ground contact, respectively. CDDCtreated wood has a light brown color and little or no odor. 

To date, CDDC treated wood is not commercially available. 

Copper HDO (CX-A) 

Copper HDO is an amine copper based preservative that has 

been used in Europe and recently standardized by the 

AWPA. The active ingredients are copper oxide, boric acid, 

and copper-HDO (Bis-(N-cyclohexyl-diazenium dioxy 

copper). The appearance and handling characteristics of 

wood treated with CX-A are similar to those of other copperbased treatments. CX-A formulations have been evaluated in 

a range of exposures, but to date have only been standardized for uses above ground. The minimum retention of copper HDO for aboveground use is 2.4 kg/m3

 (0.15 lb/ft3). To 

date, EPA registration of CX-A is pending. 

Borates 

Borate-treated wood should be used only in applications 

where the wood is kept free from rainwater, standing water, 

and ground contact. Borate preservatives are sodium salts, 

such as sodium octaborate, sodium tetraborate, and sodium 

Figure 4óLumber treated with copper citrate (CC). 

Figure 5óSupports treated with CCA and decking 

treated with copper azole (CBA-A). 
5

pentaborate, that are dissolved in water. These formulations 

have received increased attention in recent years because 

they are inexpensive and have low mammalian toxicity. 

Borate-treated wood is also odorless and colorless, and it 

may be painted or stained. 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 preservatives are standardized by the 

AWPA, but only for applications that are not exposed to 

liquid water. An example of such a use is in the construction 

of wooden buildings in areas of high termite hazard.

Practical Differences Between 

CCA Alternatives 

From a practical end-use basis, the consumer will notice 

little difference between CCA and the recently developed 

alternatives. Most residential consumers of treated wood will 

probably not even be aware that CCA has been replaced 

because all types of treated wood are referred to as ìgreentreatedî wood. The appearance, strength properties, and 

handling characteristics of CCA alternatives are very similar 

to those of CCA. CCA alternatives are slightly more expensive, however; the treated wood costs from 10% to 30% 

more than CCA-treated wood. With the possible exception 

of ACC, the alternatives also tend to be somewhat more 

corrosive to metal fasteners than is CCA. Hot-dipped 

galvanized or stainless steel fasteners should be used when 

building with wood treated with CCA alternatives. 

Environmental Concerns 

With CCA Alternatives 

Environmental and health concerns have been raised over 

the use of CCA-treated wood. It is likely that CCA alternatives will circumvent some of these concerns simply because 

they do not contain arsenic. Because they have been 

developed relatively recently and/or have been used infrequently, only limited research has been conducted on their 

potential leaching and environmental impact. Much available 

data have been obtained using small samples that accelerate 

leaching and allow more rapid comparisons between preservative formulations. Although useful as a comparative 

tool, leaching rates derived from small samples should not 

be directly extrapolated to commodity size material. 

The release and environmental impact of copper from 

ACQ-B treated wood was evaluated in a wetland boardwalk 

study (Fig. 6) (Forest Products Laboratory 2000). Elevated 

levels of copper were detected in rainwater, soil, and sediments collected adjacent to the treated wood. The rainwater 

collection indicated that release of copper peaked by 

6 months after construction, reaching average release rates 

of 35 μg per cm2

/in. of rain. Much lower average release 

rates (approximately 5 μg/cm2

/in. of rain) were observed by 

11.5 months after construction. The relatively high release of 

copper during the first 6 months of this study was reflected 

in the concentrations of copper detected in the soil; geometric mean soil concentrations were elevated by approximately 

373 lb/min (169 kg/min) directly under the edge of the 

boardwalk. However, the copper accumulations were localized in soil very close to the boardwalk; the geometric mean 

concentration was elevated by only 16 lb/min (7 kg/min), 

60 cm (24 in.) away from the boardwalk. Sediment copper 

concentrations also appeared to peak at about 6 months, 

when the geometric mean of samples removed from directly 

under the edge of the boardwalk reached 113 lb/min 

(51 kg/min), an elevation of approximately 92 lb/min 

(42 kg/min) over background levels. Copper mobility was 

greater in the sediment than in the soil, causing slight elevations in three samples removed 300 cm (10 ft) away from the 

boardwalk 11.5 months after construction. This study can 

truly be considered a ìworst caseî scenario, since the 

boardwalk decking was over-treated and inadequately conditioned (Forest Products Laboratory 2000); smaller releases 

might be expected from material treated to a retention more 

appropriate for this application. Despite the accumulations of 

copper detected in the environment, no significant impact 

was detected on the quantity or diversity of aquatic insects at 

the site (Forest Products Laboratory 2000). 

Other studies of leaching from ACQ-treated wood have been 

conducted with small specimens intended to exaggerate 

leaching and accelerate comparisons. Copper leaching from 

ACQ-B and CCA was compared in a soil-bed test with 

19- by 8- by 200-mm (0.75- by 0.30- by 7.9-in.) stakes (Jin 

and others 1992). After 9 months, copper loss from stakes 

treated to 9.6 kg/m3

 (0.6 lb/ft3) averaged 19% from ACQ-B 

and 18% from CCA. The ACQ-treated stakes also lost 30% 

of DDAC, while the CCA-treated stakes lost 11% chromium 

trioxide and 16% arsenic pentoxide. In a subsequent soil-bed 

Figure 6óEvaluation of ACQ-B treated wetland 

boardwalk for leaching and environmental impact. 
6 

test, leaching of ACQ-B and ACQ-D was compared in 

Southern Pine stakes (6 by 19 by 203 mm, 0.25 by 0.75 by 

8 in.) that had been treated to 6.4-kg/m3

 (0.4-lb/ft3) retention 

(Anon. 1994). After 3 months, ACQ-D stakes had lost 

15.4% CuO and 12.9% DDAC, and ACQ-B stakes had lost 

17.4% CuO and 32.7% DDAC (Anon. 1994). ACQ-B and 

CCA leaching data were also collected from 44-month 

ground-contact depletion tests conducted in Hilo, Hawaii, 

using 19- by 19- by 1,000-mm (0.75- by 0.75- by 39-in.) 

stakes treated to 6.4 kg/m3 (0.4 lb/ft3

) retention (Jin and 

others 1992). Averaging losses from the top, bottom, and 

middle of the stakes revealed that 21% copper oxide, 9% 

chromium trioxide, and 22% arsenic pentoxide were lost 

from CCA-treated stakes and 19% copper oxide and 42% 

DDAC were lost from ACQ-B-treated stakes. A subsequent 

study with similar size CCA-C-treated stakes reported only 

5% loss of arsenic pentoxide after 5 years of exposure in 

Florida (Anderson and Ziobro 2001). It is evident that these 

tests presented severe leaching conditions because of the 

small stake size and the extreme conditions, and the leaching 

rates should not be extrapolated to commodity size material. 

Aboveground depletion tests were conducted in Hawaii on 

51- by 19- by 356-mm (2.0- by 0.75- by 14.0-in.) CCA- and 

ACQ-B-treated Southern Pine samples (Jin and others 1992). 

After 12 months, copper oxide losses from stakes treated to 

4 kg/m3 (0.25 lb/ft3

) were 14% from ACQ-B and 8% from 

CCA. Twenty-seven percent of DDAC was lost from the 

ACQ-treated stakes, and 14% chromium trioxide and 19% 

arsenic pentoxide were lost from the CCA-treated stakes. A 

similar test was conducted with samples treated with ACQ-D 

and CCA-C. After 6 months, the ACQ-D samples treated to 

4 kg/m3

 (0.25 lb/ft3) had lost approximately 10% copper 

oxide and 32% DDAC, and the CCA-C treated samples had 

lost 9% copper oxide (Anon. 1994). 

In a study that provides insight into leaching rates of treated 

wood exposed aboveground under in-service conditions, 

depletion tests were conducted on decks built with 38- by 

140-mm (1.5- by 5.5-in.) lumber that had been treated with 

CCA-C, ACQ-B, or copper boron (Cu:BAE = 25:25) with 

formulation characteristics similar to those of CBA-A (Fox 

and others 1994). The boards were treated with either full 

cell or empty cell processes to a retention of 4 kg/m3 

(0.25 lb/ft3) copper for copper boron or a total retention of 

6.4 kg/m3

 (0.4 lb/ft3) with either ACQ-B or CCA-C. During 

20 months in Conley, Georgia, the decks were exposed to 

more than 2 m (80 in.) of rainfall, which was periodically 

collected and analyzed for copper and boron. The copperñ

boron decks leached 8% to 12% copper and 55% to 65% 

boric acid, the ACQ-B decks lost 8% to 10% copper, and the 

CCA-treated decks lost 5% copper. These losses corresponded to leaching rates of approximately 1,722 and 

1,184 μg/cm2 (0.0035 and 0.0024 lb/ft2

) for copper for the 

copperñboron-treated material, 1,292 and 969 μg/cm2 

(0.0026 and 0.0020 lb/ft2) for the ACQ-B treated material, 

and 215 and 161 g/m2 (0.0004 and 0.0003 lb/ft2

) for the 

CCA-treated material for modified full-cell and full-cell 

treatments, respectively. With both types of treating schedules, copper loss from the copperñboron-treated wood was 

greatest during the first 508 mm (20 in.) of rainfall and 

minimal during the last 254 mm (10 in.) of rainfall. 

A 5-year study of copper loss from 178- to 229-mm- (7- to 

9-in-) diameter Southern Pine pole stubs that had been 

treated with copper citrate to a target retention of 9.6 kg/m3

(0.6 lb/ft3

) was conducted in Gainesville, Florida (Anderson 

and others 1993). The researchers removed increment cores 

from 152 mm (6 in.) below ground, at groundline, and 

610 mm (24 in.) above ground before exposure and 12, 24, 

36, 48, and 60 months after exposure. Leaching data were 

variable between sampling periods, but copper losses of 

approximately 50%, 10%, and 39% were noted for the 0 to 

13, 13 to 25, and 25 to 52 mm (0 to 0.5, 0.5 to 1, and 1 to 

2 in.) assay zones, respectively, in the below-ground zone 

after 5 years. The authors estimate a total copper loss of 

approximately 28% from the below-ground zone during the 

first year, with minimal losses in subsequent years. 

Also pertinent to the leaching of boron and copper from 

ammoniacal formulations was a study evaluating leaching 

from 38- by 89-mm (1.5- by 3.5-in.) stakes treated with 

ammoniacal copper borate and exposed for 11 years at a test 

site in Mississippi (Johnson and Foster 1991). The original 

copper oxide retention in the stakes varied from 0.29% to 

1.98%, and the boric acid content varied from 0.10% to 

0.71%. During exposure, 95% to more than 99% of the 

boron leached from the groundline portion of the stakes and 

78% to 93% of the boron was lost from the aboveground 

portion. Copper losses varied from 3% to 33% in the 

groundline portion of the stakes and 0 to 28% in the 

aboveground portion. With both copper and boron, the 

greatest percentage of loss occurred at the lower retention 

levels. Because of the relatively large dimensions of the 

stakes used in this study, the leaching rates noted for ammoniacal copper may be more representative of losses in service 

than are stake test data reported previously for other 

ammoniacal formulations. 

The release and environmental accumulation of copper from 

CDDC-treated wood was recently evaluated in a wetland 

boardwalk study (Forest Products Laboratory 2000) (Fig. 7). 

During the first three post-construction inspections, copper 

concentrations immediately adjacent to the boardwalk 

slowly increased; 5.5 months after construction, the average 

copper level in the top 15 cm (5.9 in.) of soil was only 

28 lb/min (13 kg/min) higher than the average preconstruction level. This trend changed at the 11-month inspection, 

when the combination of sand applied to the walkway and 

heavy rainfall increased geometric mean soil copper levels 

immediately adjacent to the boardwalk to a level approximately 135 lb/min (61 kg/min) higher than preconstruction 

levels. 
7

It is likely that much of the increase in soil copper during 

this period was due to removal of wood particles by abrasion, and that copper levels would have been lower if sand 

had not been applied to the boardwalk. However, one can 

conclude that sand should not be applied to CDDC-treated 

wood (or probably other types of treated wood) when it is 

used in areas where release of copper into the environment 

is a concern. 

It is notable that soil movement of the copper was apparently 

quite limited; during the course of the study, only a few of 

the samples removed 15 cm (6 in.) away from the boardwalk 

contained elevated levels of copper, and the maximum copper concentration detected at greater distances from the 

wood was 37 lb/min (17 kg/min). Copper movement downward in the soil was also quite limited; the vast majority of 

copper leached was confined within the top 15 cm (6 in.) of 

the soil. Thus, it appears that any environmental contamination is restricted to immediately adjacent to the wood when 

CDDC-treated wood is used in or over soil. 

Long-term (23 years) leaching data were reported for CDDC 

for 19- by 19- by 457-mm (0.75- by 0.75- by 18-in.) Southern Pine stakes exposed in Bainbridge, Georgia (Freeman 

and others 1994). The stakes were treated to either 9.6 kg/m3

(0.6 lb/ft3

) with CCA or to 3.5 kg/m3 (0.22 lb/ft3) (as copper) 

with a CDDC formulation in which copper sulfate was the 

copper source. Copper retention levels in the above- and 

below-ground portions of the stakes were compared to estimate preservative leaching. The CDDC-treated stakes had 

77% less copper below than above ground, and the CCA-C 

treated stakes had 72% less copper below than above 

ground. Actual copper losses may have been greater because 

some leaching did occur above ground. These leaching rates 

may sound extreme, but it is important to remember the 

length of the test and that small-sized stakes lose a much 

greater percentage of their preservative than does productsized material. 

Little information is available on the rate of leaching from 

ACC-treated wood. One study compared the depletion of 

ACC and an older formulation of CCA (CCA-A) from several softwood species of cooling tower slats (Gjovik and 

others 1972). After 10 years, average depletion from the 

ACC-treated slats was approximately 35%, while that from 

the CCA-A treated slats was 25%. The unusual dimensions 

of the slats (10-mm by 32-mm by 182-cm, 0.375- by 1.25- 

by 71.5-in.) and the unique exposure environment make it 

difficult to compare the leaching results to other applications. However, the results do suggest that the rate of depletion from ACC-treated wood is comparable to or slightly 

greater than that from CCA-A treated wood. The ACC treatment solution does utilize hexavalent chromium, but the 

chromium is converted to the more benign trivalent state 

during treatment and subsequent storage of the wood. ACC 

treatment solutions contain a higher proportion of hexavalent 

chromium than do CCA solutions, and recent research indicates that a longer reaction period is needed for ACC 

(Pasek 2003). 

The literature indicates that all the CCA alternatives will 

release copper into the environment at a rate greater than or 

equal to that of CCA. This is not surprising because all of 

the recently standardized CCA alternatives contain several 

times as much copper (proportionally) as does CCA. Fortunately, copper is associated with fewer mammalian health 

concerns than is arsenic. Environmental release of cobiocides such as boron or quaternary ammonium compounds 

is also to be expected, but these co-biocides also have relatively low mammalian toxicity. The CCA alternatives may 

not offer significant advantages over CCA in aquatic applications or other applications where copper release might be a 

concern. From this perspective, the recent label changes on 

allowable uses of CCA are logical. CCA will still be allowed 

for most aquatic uses, while arsenic-free alternatives will be 

used where human exposure is greatest. 

Leaching from wood treated with water-based preservatives 

is also dependent on completion of fixation reactions. The 

active ingredients of various waterborne wood preservatives 

(copper, chromium, arsenic, and/or zinc) are initially watersoluble in the treating solution but become resistant to leaching when placed into the wood. This leaching resistance is a 

result of the chemical ìfixationî 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. For each type 

of preservative, some reactions occur very rapidly during 

pressure treatment, while others may take days or even 

weeks to reach completion, depending on post-treatment 

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 

Figure 7óThis CDDC-treated boardwalk is being 

evaluated for leaching and environmental 

accumulation of copper. 
8 

many times greater than that for wood that has been adequately conditioned. Concerns about inadequate fixation 

have led Canada and European countries to develop standards or guidelines for ìfixingî treating wood. The AWPA 

has recently formed several task forces to consider the development of fixation or ìleaching minimizationî standards 

for CCA-C and other wood preservatives, but as yet there 

are no nationally recognized standards for fixation of waterborne preservatives in the United States. In addition, an ongoing effort is underway to develop Best Management Practice (BMP) type standards to ensure that treated wood is 

produced in a way that will minimize environmental and 

handling concerns. The Western Wood Preserversí Institute 

(WWPI) has developed guidelines for treated wood used in 

aquatic environments (WWPI 1996), and the AWPA has 

active task forces working to develop guidelines for waterborne preservatives. As BMP-type standards are developed, 

it will be important to include them in specifications of 

treated wood products. 

As researchers continue to respond to environmental concerns, further progress will be made in reducing environmental impacts from preservative treated wood. Current 

preservatives are used in a broad range of applications, 

ranging from mild to very severe deterioration hazards. 

Because of this, the amount or type of chemical used is 

stronger than necessary for many applications. Future preservative treatments may be more closely aligned with certain types of applications, allowing use of less toxic chemicals in many applications. In addition, greater emphasis will 

be placed on using the minimum amount of preservative 

needed to protect the wood. This stratification has already 

begun; some manufacturers are offering decking treated to a 

lower retention than are the stringers, which may be treated 

to a lower retention than are support posts (Fig. 8). 

This evolution will require changes in the way that treated 

wood is currently marketed and specified. 

To guide selection of the types of preservatives and loadings 

appropriate to a specific end-use, the AWPA recently developed Use Category System (UCS) standards (AWPA 2001). 

The UCS standards simplify the process of finding appropriate preservatives and preservative retentions for specific 

end-uses. The UCS standards categorize all treated wood 

applications by the severity of the deterioration hazard. For 

example, the lowest category, Use Category 1 (UC1) is for 

wood that is used in interior construction, completely protected from the weather. At the other end of the spectrum is 

UC5, which encompasses applications that place treated 

wood in contact with seawater and marine borers. To use the 

UCS standards, one only needs to know the intended enduse of the treated wood. 

Concluding Remarks 

The treated wood industry is undergoing a major transition 

as CCA is replaced in most residential applications. CCA 

alternatives have been developed and are becoming more 

widely available. The alternatives rely heavily on copper as 

the primary biocide, with a range of co-biocides to help 

protect against copper-tolerant organisms. Studies indicate 

that the CCA alternatives do release measurable quantities of 

copper and co-biocide into the environment. However, these 

components have lower mammalian toxicity than does arsenic, and they are less likely to raise concerns about environmental impacts. As the treated wood industry evolves, it is 

likely that a wider range of types and retentions of wood 

preservatives will become available, with the treatment more 

closely tailored to a specific type of construction application. 

Literature Cited 

Anderson, T.C.; Ziobro, R.J. 2001. Residual levels of 

CCA-C in 3/4î × 3/4î × 18î Southern Pine stakes exposed to 

one, three and five years in Gainsville, FL. Technical Forum 

Presentation, American Wood Preservers Association 

Annual Meeting, Minneapolis, MN. 

Anderson, T.C.; Inwards, R.D.; Leach, R.M. [and others]. 1993. A proposal for the standardization of ammoniacal 

copper citrate. Submitted to American Wood Preserversí 

Association Committee P-4 and the General Preservatives 

Committee. Buffalo, NY: Osmose Wood Preserving, Inc. 

Anon. 1994. ACQ Type D. Proposal to the AWPA technical 

committees to include ACQ type D in Standards P5, C1, C2, 

C15, C9, and M6. Charlotte, NC: Chemical Specialties, Inc. 

AWPA. 2001. Book of Standards. Granbury, TX: American 

Wood Preservers Association. Figure 8óStacks of ACQ-C and CA-B treated lumber 

await sale at a lumberyard. Multiple retentions are 

available for different end-uses. 
9

Clausen, C.A.; Green, F. III. 2003. Copper tolerance of 

brown-rot fungi: time course of oxalic acid production. 

International Biodeterioration and Biodegradation. 

51:145ñ149. 

Freeman, M.H.; Stokes, D.K.; Woods, T.L; Arsenault, 

R.D. 1994. An update on the wood preservative copper 

dimethyldithiocarbamate. In: Proceedings, American Wood 

Preserversí Association. 90: 67ñ87. 

Forest Products Laboratory. 2000. Environmental impact 

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

Pap. FPLñRPñ582. Madison, WI: U.S. Department of Agriculture, Forest Service, Forest Products Laboratory. 126 p. 

Fox, R.F.; Pasek, E.A.; Deshan, P.N. [and others]. 1994. 

Copper azole wood preservatives. Proposal to the American 

Wood Preserversí Association Committees to include copper 

azole type A in AWPA Standard P-5. July 12, 1994. Conley, 

GA: Hickson Corporation. 

Gjovik, L.R; Bendtsen, B.A.; Roth, H.G. 1972. Condition 

of preservative-treated cooling tower slats after 10 years of 

service. Forest Products Journal. 22(4): 35ñ40. 

Jin, L.; Archer, K.; Preston, A.F. 1992. Depletion and 

biodeterioration studies with developmental wood preservative formulations. In: Proceedings, American Wood Preserversí Association; 108ñ125. 

Johnson, B.R.; Foster, D.O. 1991. Preservative loss from 

stakes treated with ammoniacal copper borate. Forest 

Products Journal. 41(9): 59ñ63. 

Lebow, S.T.; Hatfield, C.A.; Crawford, D.M.; and 

Woodward, B. 2003. Long-term stake evaluations of waterborne copper systems. In: Proceedings, 2003 American 

Wood Preserversí Association annual meeting, Boston, MA. 

In press. http://www.awpa.com/papers/Lebow_2003.pdf 

Pasek, E. 2003. Minimizing preservative losses: Fixation. A 

report of the P4 Migration/Depletion/ Fixation Task Force. 

In: Proceedings, 2003 American Wood Preserversí Association annual meeting, Boston, MA. In press. 

http//www.awpa.com/papers/Eugene_Pasek.pdf 

WWPI. 1996. Best management practices for the use of 

treated wood in aquatic environments. Vancouver, WA: 

Western Wood Preservers Institute. 35 p.