Chromated copper arsenate (CCA) is a

wood preservative Wood easily degrades without sufficient preservation. Apart from structural wood preservation measures, there are a number of different chemical preservatives and processes (also known as "timber treatment", "lumber treatment" or "pressure treat ...

containing compounds of

chromium Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

copper Copper is a chemical element with the symbol Cu (from la, cuprum) 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 pink ...

, and

arsenic Arsenic is a chemical element with the symbol As and atomic number 33. Arsenic occurs in many minerals, usually in combination with sulfur and metals, but also as a pure elemental crystal. Arsenic is a metalloid. It has various allotropes, b ...

, 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,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...

s and

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pa ...

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 (Hindi: ), 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 and dependencies by population, second-most populous ...

n chemist Sonti Kamesam, and patented in

Britain Britain most often refers to: * The United Kingdom, a sovereign state in Europe comprising the island of Great Britain, the north-eastern part of the island of Ireland and many smaller islands * Great Britain, the largest island in the United King ...

in 1934. It has been used for

timber treatment Wood easily degrades without sufficient preservation. Apart from structural wood preservation measures, there are a number of different chemical preservatives and processes (also known as "timber treatment", "lumber treatment" or "pressure tre ...

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 executive agency of the United States federal government tasked with environmental protection matters. President Richard Nixon proposed the establishment of EPA on July 9, 1970; it ...

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 property of a body. It was traditionally believed to be related to the quantity of matter in a physical body, until the discovery of the atom and particle physics. It was found that different atoms and different ele ...

percentages of

chromium trioxide Chromium trioxide (also known as chromium(VI) oxide or chromic anhydride) is an inorganic compound with the formula CrO3. It is the acidic anhydride of chromic acid, and is sometimes marketed under the same name. This compound is a dark-purple s ...

or "chromic acid" , arsenic pentoxide , 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. It ...

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

chromic acid The term chromic acid is usually used for a mixture made by adding concentrated sulfuric acid to a dichromate, which may contain a variety of compounds, including solid chromium trioxide. This kind of chromic acid may be used as a cleaning mixtu ...

, copper oxide, and

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

(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 Chromium is a chemical element with the symbol Cr and atomic number 24. It is the first element in group 6. It is a steely-grey, lustrous, hard, and brittle transition metal. Chromium metal is valued for its high corrosion resistance and hard ...

and/or copper(II) arsenate , 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 formula , a polysaccharide consisting of a linear chain of several hundred to many thousands of β(1→4) linked D-glucose units. Cellulose is an important structural component of the primary cell wa ...

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 rigidity a ...

. 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 were ...

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 dis ...

. 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(II) complex and quaternary ammonium alkyl- or aryl-substituted compounds ("quats"). Thus the product was original ...

(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 A biophysical environment is a biotic and abiotic surrounding of an organism or population, and consequently includes the factors that have an influence in their survival, development, and evolution. A biophysical environment can vary in scale ...

(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 in which some honey bee species of the subgenus '' Apis'' live and raise their young. Though the word ''beehive'' is commonly used to describe the nest of any bee colony, scientific and professional literature ...

construction has been associated with increased levels of arsenic in the

honey Honey is a sweet and viscous substance made by several 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 plants (primar ...

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 activity ...

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. kaolin, Al2 Si2 O5( OH)4). Clays develop plasticity when wet, due to a molecular film of water surrounding the clay pa ...

or soils that are more

alkali In chemistry, an alkali (; from ar, القلوي, al-qaly, lit=ashes of the saltwort) is a basic, ionic 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 ...

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 zoster or herpes zoster, 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 fac ...

, permanent wood foundations, 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 located primarily in Europe, Europe. The union has a total area of ...

and

Australia Australia, officially the Commonwealth of Australia, is a sovereign country comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands. With an area of , Australia is the largest country by ...

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 30 Ju ...

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

Case Studies in Environmental Medicine - Arsenic Toxicity

Case Studies in Environmental Medicine - Chromium Toxicity

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