Chromated copper arsenate
**Composition and Application:**
– Chromated copper arsenate (CCA) products contain chromium trioxide, arsenic pentoxide, and copper(II) oxide in specific mass percentages.
– The preservative is applied as a water-based mixture with 0.6–6.0% of chromic acid, copper oxide, and arsenic acid.
– The mixture is infused into wood at high pressure to protect it from decay and insects.
– Arsenic in treated wood is believed to be in the form of chromium (III) arsenate and/or copper(II) arsenate.
– The pH of the mixture ranges from 1.6–2.5.
**Mechanism of Action:**
– Chromium aids in fixing chemicals in the wood, copper protects against decay, fungi, and bacteria, while arsenic acts as the main insecticidal component.
– Arsenic provides protection from wood-attacking insects like termites and marine borers.
– CCA-treated timber has improved weather resistance and long-term paint adherence.
– These compounds are toxic when inside the bloodstream, especially from burning treated wood.
**Alternatives:**
– Heavy-duty preservatives like creosote and pentachlorophenol are alternatives to CCA.
– Water-borne preservatives such as alkaline copper quaternary (ACQ) compounds and copper azole (CuAz) are safer options.
– Pressure and heat-treated lumber, although more expensive, do not contain chemicals.
– Some lumber may be pressure treated with water alone, providing resistance to mold and water damage.
– Chemically treated lumber offers long-term robust qualities and resistance.
**Safety Concerns:**
– Concerns over CCA focus on its chromium and arsenic contents.
– Arsenic, a known carcinogen, has negative health effects in inorganic form.
– Exposure to CCA can lead to itching, rashes, neurological symptoms, and breathing problems.
– Regulatory actions have been taken to address the safety risks associated with CCA.
**Handling and Health Implications:**
– Contact with unmarked chromated arsenical wood preservatives can cause itching, rashes, and breathing problems.
– Studies have suggested that CCA-treated playgrounds could pose risks to children’s health.
– Machining CCA-treated wood exposes workers to chronic and acute health risks.
– Animals may need to ingest large amounts of CCA-treated wood to be poisoned, but burned timber ashes are more toxic.
Chromated copper arsenate (CCA) is a wood preservative containing compounds of chromium, copper, and arsenic, 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 microbes and insects. Like other copper-based wood preservatives, it imparts a greenish tint to treated timber.
CCA was invented in 1933 by Indian chemist Sonti Kamesam, and patented in Britain 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 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.