Health/Toxics: Arsenic in Treated Wood

Despite arsenic's dark history, the United States has been a leading consumer of arsenic for many years.

From the mid-19th century to 1940s, inorganic arsenic compounds were the dominant pesticides used by U.S. farmers and fruit growers, according to the National Toxicology Program, an interagency effort hosted within the National Institutes of Health.

Beginning in the 1960s, as scientists recognized inorganic arsenic as a human carcinogen and as the U.S. Safe Drinking Water Act of 1975 focused on reducing arsenic in water supplies, nearly all pesticides based on inorganic compounds were banned or voluntarily pulled from the market. The Environmental Protection Agency is phasing out the use of organic arsenic compounds, considered less toxic, on sod farms and golf courses as of Dec. 31, 2012. One organic arsenic pesticide, monosodium methanearsonate, is still permitted, with certain precautions, for use to fight pigweed on cotton. EPA says it will review this use in 2013.

The U.S. stopped producing arsenic in 1985. But arsenic trioxide was still in great demand as the basis for chromated copper arsenate, a common wood preservative used to make "pressure-treated" lumber for outdoor use. According to the U.S. Geological Survey, between 2001 and 2003, the U.S. imported more than 20,000 metric tons of arsenic trioxide a year, most of which was used to make wood preservative.

In 2001, the Environmental Working Group launched its Poisoned Playgrounds initiative to build support for a ban on arsenic in all consumer products. An EWG analysis entitled The Poisonwood Rivals found that pressure treated wood sold by Home Depot and Lowe's Home Improvement Warehouse leached about 100 times the U.S. Environmental Protection Agency's 10 microgram "allowable daily exposure level" for drinking water onto a moistened wipe the size of a four-year-old's hand.

The next year, under pressure by EWG and other consumer groups, members of Congress and the Environmental Protection Agency, the wood industry agreed to stop using arsenic-based wood preservatives for residential lumber, as of December 2003. (The industry retained arsenic-based non-residential wood treatments).

The market changed dramatically as result. Imports dropped to an average of 6,900 tons a year between 2004 and 2009, according to USGS, and remained low at 4900 tons in 2010.

The U.S. Food and Drug Administration has authorized several organic arsenic compounds for use in small amounts as antimicrobials in animal and poultry feeds. (Upper limits: 0.5 parts per million in uncooked chicken, turkey, pork and eggs.)

Arsenic is used to make ammunition, lead-acid storage batteries, bearings, lead shot, wheel weights, gallium-arsenide semiconductors for solar cells, space research and telecommunication and germanium-arsenide-selenide specialty optical materials.