Chromated copper arsenate (CCA) is a

wood preservative Wood preservation refers to any method or process, or even technique, used to protect the wood and extend its service life. Most wood species are susceptible to both biological (''biotic'') and non-biological (''abiotic'') factors that cause d ...

containing compounds of

chromium Chromium is a chemical element; it has Symbol (chemistry), symbol Cr and atomic number 24. It is the first element in Group 6 element, group 6. It is a steely-grey, Luster (mineralogy), lustrous, hard, and brittle transition metal. Chromium ...

copper Copper is a chemical element; it has symbol Cu (from Latin ) and atomic number 29. It is a soft, malleable, and ductile metal with very high thermal and electrical conductivity. A freshly exposed surface of pure copper has a pinkish-orang ...

, and

arsenic Arsenic is a chemical element; it has Symbol (chemistry), symbol As and atomic number 33. It is a metalloid and one of the pnictogens, and therefore shares many properties with its group 15 neighbors phosphorus and antimony. Arsenic is not ...

, in various proportions. It is used to impregnate timber and other wood products, especially those intended for outdoor use, in order to protect them from attack by

microbe A microorganism, or microbe, is an organism of microscopic size, which may exist in its single-celled form or as a colony of cells. The possible existence of unseen microbial life was suspected from antiquity, with an early attestation in ...

s and

insect Insects (from Latin ') are Hexapoda, hexapod invertebrates of the class (biology), class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body (Insect morphology#Head, head, ...

s. Like other copper-based wood preservatives, it imparts a greenish tint to treated timber. CCA was invented in 1933 by

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

n chemist

Sonti Kamesam Sonti Kamesam (1890–30 November 1952) was an Indian timber engineer and scientist who worked at the Forest Research Institute, Dehra Dun. He is best known for his patented wood preservative, ASCU, from the chemical symbols for Arsenic and Copper ...

, and patented in

Britain Britain most often refers to: * Great Britain, a large island comprising the countries of England, Scotland and Wales * The United Kingdom of Great Britain and Northern Ireland, a sovereign state in Europe comprising Great Britain and the north-eas ...

in 1934. It has been used for timber treatment since the mid-1930s, and is marketed under many trade names. In 2003, the

United States Environmental Protection Agency The Environmental Protection Agency (EPA) is an independent agency of the United States government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it began operation on De ...

and the lumber industry agreed to discontinue the use of CCA-treated wood in most residential construction. This agreement was intended to protect the health of humans and the environment by reducing exposure to the arsenic in CCA-treated wood. As a result of this decision, CCA-treated wood can no longer be used to construct residential structures such as playground equipment, decks, picnic tables, landscaping features, fences, patios, and walkways. Acute intoxication due to mishandling of treated products, e.g. by burning, is also a serious concern. Nevertheless, CCA remains a popular and economical option to make perishable timbers, such as plantation-grown pine, viable for applications like poles, piling, retaining structures, etc.

Composition and application

The composition of CCA products is usually described in terms of the

mass Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...

percentages of

chromium trioxide Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula . It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple solid ...

or "chromic acid" ,

arsenic pentoxide Arsenic pentoxide is the inorganic compound with the formula As2O5. This glassy, white, deliquescent solid is relatively unstable, consistent with the rarity of the As(V) oxidation state. More common, and far more important commercially, is arse ...

, and

copper(II) oxide Copper(II) oxide or cupric oxide is an inorganic compound with the formula CuO. A black solid, it is one of the two stable oxides of copper, the other being Cu2O or copper(I) oxide (cuprous oxide). As a mineral, it is known as tenorite, or so ...

. The preservative is applied as a water-based mixture containing 0.6–6.0% (by weight) of

chromic acid Chromic acid is a chemical compound with the chemical formula . It is also a jargon for a solution formed by the addition of sulfuric acid to aqueous solutions of dichromate. It consists at least in part of chromium trioxide. The term "chromic ...

, copper oxide, and

arsenic acid Arsenic acid or arsoric acid is the chemical compound with the chemical formula, formula . More descriptively written as , this colorless acid is the arsenic analogue of phosphoric acid. Arsenate and phosphate salts behave very similarly. Arsenic ...

(USDA, 1980), with pH 1.6–2.5. The mixture is infused into wood at high pressure. In the treated wood, arsenic is believed to be in the form of chromium (III) arsenate and/or

copper(II) arsenate Copper arsenate (Cu3(AsO4)2·4H2O, or Cu5H2(AsO4)4·2H2O), also called copper orthoarsenate, tricopper arsenate, cupric arsenate, or tricopper orthoarsenate, is a blue or bluish-green powder insoluble in water and alcohol and soluble in aqueous a ...

, or fairly stable chromium dimer-arsenic clusters.

Mechanism of action

The

acts as a chemical fixing agent and has little or no preserving properties; it helps the other chemicals to fix in the timber, binding them through chemical complexes to the wood's

cellulose Cellulose is an organic compound with the chemical formula, formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of glycosidic bond, β(1→4) linked glucose, D-glucose units. Cellulose is an important s ...

and

lignin Lignin is a class of complex organic polymers that form key structural materials in the support tissues of most plants. Lignins are particularly important in the formation of cell walls, especially in wood and bark, because they lend rigidit ...

. The copper acts primarily to protect the wood against decay, fungi, and bacteria, while the arsenic is the main insecticidal component, providing protection from wood-attacking insects including termites and marine borers. It also improves the weather resistance of treated timber and may assist paint adherence in the long term. These compounds are toxic to the human system when inside the bloodstream, usually from burning wood treated with these compounds which is very dangerous.

Alternatives

Alternative heavy-duty preservatives include

creosote Creosote is a category of carbonaceous chemicals formed by the distillation of various tars and pyrolysis of plant-derived material, such as wood, or fossil fuel. They are typically used as preservatives or antiseptics. Some creosote types w ...

and

pentachlorophenol Pentachlorophenol (PCP) is an organochlorine compound used as a pesticide and a disinfectant. First produced in the 1930s, it is marketed under many trade names. It can be found as pure PCP, or as the sodium salt of PCP, the latter of which disso ...

. Similar water-borne preservatives include

alkaline copper quaternary Alkaline copper quaternary, usually abbreviated ACQ, is a type of water-based wood preservative product containing a soluble copper#Coordination chemistry, copper(II) complex and quaternary ammonium alkyl- or aryl-substituted compounds ("quats"). ...

(ACQ) compounds, copper azole (CuAz), ammoniacal copper zinc arsenate (ACZA), copper citrate, and copper HDO (CuHDO). Usually more expensive options, but safer, are pressure and heat treated lumber which contains no chemicals. Usually they lack the long-term robust qualities and resistance of chemically treated lumber. Some may be pressure treated with water alone, which while much more long lived than normal wood, will not repel insects as much as chemically treated but will resist mold and water damage much more than non-treated lumber.

Safety

Concerns over the safety of CCA have focused on its chromium and arsenic contents.(2015):
CHROMATED COPPER ARSENATE (CASRN: 37337-13-6)
. Online document at the National Library of Medicine (NLM), Special Information Services(SIS), National Institute of Medicine and Health (NIMH). Revision of 2015-02-18, accessed on 2019-04-16. Arsenic is found naturally in the soil, food and water, and is still used to treat some medical conditions. However it has a long list of negative health effects, especially in inorganic form, by contact or by ingestion, and was designated a human carcinogen by the U.S.

Environmental Protection Agency Environmental Protection Agency may refer to the following government organizations: * Environmental Protection Agency (Queensland), Australia * Environmental Protection Agency (Ghana) * Environmental Protection Agency (Ireland) * Environmenta ...

(EPA) in 1986 (even though its actual risk remains unclear). Arsenic in drinking water is a serious public health problem in some areas of the world.

Handling

Itching, burning rashes, neurological symptoms, and breathing problems have been associated with handling unmarked chromated arsenical wood preservatives, including contact with the sap draining from treated wood. Regulatory action was motivated in the 1990s by studies suggesting that CCA could pose a risk to children in playgrounds built with CCA-treated timber. Later studies however found that, while concentrations of arsenic in the soil and hand rinses were considerably higher among children who played on CCA-treated playground toys than in the control group, there was no significant difference in the arsenic concentrations in urine and saliva samples.Shalat SL, Solo-Gabriele HM, Fleming LE, Buckley BT, Black K, Jimenez M, Shibata T, Durbin M, Graygo J, Stephan W, Van De Bogart G (2006): "A pilot study of children's exposure to CCA-treated wood from playground equipment". ''Science of the Total Environment'', volume 367, issue 1, pages 80-88.

Working

Machining (sawing, sanding, drilling) CCA-treated wood also exposes construction workers and amateur carpenters to chronic and acute health risks via inhalation.

Animals

CCA treated wood has relatively low toxicity, and animals would need to ingest unlikely amounts (28 g daily for a month, for an adult horse) in order to become poisoned. However, ashes from burned timber are much more toxic, and cattle have been poisoned in this way.Peter D. Constable and Kenneth W. Hinchcliff and Stanley H. Done and Walter Grünberg (2017): "Systemic and Multi-Organ Diseases". Chapter 21 (pages 2002-2214) of ''Veterinary Medicine'', 11th edition. W. B. Saunders. Use of CCA-treated wood for

beehive A beehive is an enclosed structure which houses honey bees, subgenus '' Apis.'' Honey bees live in the beehive, raising their young and producing honey as part of their seasonal cycle. Though the word ''beehive'' is used to describe the nest of ...

construction has been associated with increased levels of arsenic in the

honey Honey is a sweet and viscous substance made by several species of bees, the best-known of which are honey bees. Honey is made and stored to nourish bee colonies. Bees produce honey by gathering and then refining the sugary secretions of pl ...

and winter loss of bee colonies.Martins A. Kalnins and Benjamin F. Detroy (1984): "The effect of wood preservative treatment of beehives on honey bees and hive products". ''Journal of Agricultural and Food Chemistry'', volume 32, issue 5, pages 1176–1180.

Releases to the environment

Another concern is the leaching of chromium and arsenic from CCA-treated timber and their release to the environment. The amount and rate of arsenic leaching varies considerably depending on numerous factors, such as local climate, acidity of rain and soil, age of the wood product, and how much CCA was applied. A study has found that

soil contamination Soil contamination, soil pollution, or land pollution as a part of land degradation is caused by the presence of xenobiotic (human-made) chemicals or other alteration in the natural soil environment. It is typically caused by industrial activit ...

due to the presence of CCA-treated wood after 45 years was minimal. Many studies in less aggressive soil types show leaching to be as low as 0.5 ppm (red pine poles in service,) or up to 14 ppm (treated pine in garden beds). Should any chemicals leach from the wood they are likely to bind to soil particles, especially in soils with

clay Clay is a type of fine-grained natural soil material containing clay minerals (hydrous aluminium phyllosilicates, e.g. kaolinite, ). Most pure clay minerals are white or light-coloured, but natural clays show a variety of colours from impuriti ...

or soils that are more

alkali In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...

ne than neutral. Sawdust and other residues left over by construction may be a much more significant source of arsenic pollution to soil and environment than leaching from the final timber structure.Jennifer K. Saxe, Teresa S. Bowers, and Kim Reynolds Reid (1964): "Arsenic". Chapter 13 (pages 279-292) of ''Environmental Forensics - Contaminant Specific Guide''. Academic Press.

Burning

Acute and chronic arsenicism have been reported to result from inhalation of smoke from burning of CCA-treated wood, such as in the use of scrap timber as fuel for industrial or domestic fires.Amy Yuntzu-Yen Chen and Thomas Olsen (2016): "Chromated copper arsenate–treated wood: a potential source of arsenic exposure and toxicity in dermatology". ''International Journal of Women's Dermatology'', volume 2, issue 1, pages 28–30.

Regulatory status

CCA manufacture and use are regulated by various national and international standards, such as AWPA P23-10 for the US and SANS 673 for South Africa. In the US, the use of CCA to treat timber for residential use has been banned since December 2003. Timber treated before that date was still allowed to be sold, but retailers were required provide warning labels. Treated timber products already in use, including playsets and decks, were allowed to remain in place. Exceptions to the restrictions were allowed, including the treatment of shakes and

shingles Shingles, also known as herpes zoster or zona, is a viral disease characterized by a painful skin rash with blisters in a localized area. Typically the rash occurs in a single, wide mark either on the left or right side of the body or face. T ...

, permanent wood

foundations Foundation(s) or The Foundation(s) may refer to: Common uses * Foundation (cosmetics), a skin-coloured makeup cream applied to the face * Foundation (engineering), the element of a structure which connects it to the ground, and transfers loads f ...

, and certain commercial applications. The EPA has also issued regulations for the industrial application of CCA to wood. CCA has been phased out of residential use also in Canada. Regulatory agencies in the

European Union The European Union (EU) is a supranational union, supranational political union, political and economic union of Member state of the European Union, member states that are Geography of the European Union, located primarily in Europe. The u ...

and

Australia Australia, officially the Commonwealth of Australia, is a country comprising mainland Australia, the mainland of the Australia (continent), Australian continent, the island of Tasmania and list of islands of Australia, numerous smaller isl ...

also prohibited CCA-treated timber in residential uses, while considering that timber already in place need not be replaced. In 2003, the

Environmental Risk Management Authority The Environmental Risk Management Authority (ERMA; ) was a New Zealand government agency that controlled the introduction of hazardous substances and new organisms (invasive species and genetically modified organisms). It was disestablished on 3 ...

in New Zealand decided to not restrict CCA use for any applications, but notes that few well-designed studies have been carried out of those using CCA or CCA-treated timber.http://www.epa.govt.nz/Publications/cca-report.pdf - Timber Treatment Chemicals

Safety recommendations

The EPA recommends wearing gloves when handling CCA-treated wood, wearing goggles and masks when sawing or sanding it, and never burning it. CCA-treated wood should not be used where it may come in contact with food, such as in kitchen tops, cutting boards, or

s. It should not be exposed to chemicals such as bleaches, acids, soda, etc. Timber should be inspected for residues of CCA on the surface that could easily be dislodged. Sealants or other coatings will reduce the risk of environmental contamination. Disposal of scrap and waste CCA-treated timber should be done only in approved incinerators or controlled landfill sites, which are designed to handle potentially toxic wastes such as paints, insecticides, batteries, etc.

References

External links

National Pesticide Information Center - Chromated Copper Arsenate (CCA): Guide to selected resources

{{Insecticides Arsenates Chromates Copper(II) compounds Inorganic insecticides Fungicides Pesticides Pollutants Indian inventions