AUGUSTA – Lumber suppliers estimate a statewide ban on arsenic-treated wood will cause costs to rise by about 20 percent over the next year.

State legislators this week approved a first-in-the-nation ban on the sale of arsenic-treated lumber for use in residential construction.

Gov. John E. Baldacci is expected to sign off on the ban, which would take effect next April.

The vote followed a voluntary agreement last year between federal environmental regulators and the wood-treating industry to phase out production of arsenic-treated lumber across the nation by 2004.

Most Maine lumber companies saw the change coming and had already begun converting to wood treated with an alternative to arsenic.

“I would say if you took an informal poll of the dealers in Maine that 75 percent are either arsenic-free or are in the process of converting,” said Matt Masse, who purchases lumber for Hammond Lumber Co.

Arsenic is a known carcinogen and can leach out of structures built with pressure-treated lumber over time if the lumber is not properly sealed with varnish or paint, according to some assessments.

State toxicologist Andy Smith said the danger is that the poisonous element can end up on the hands and eventually in the mouths of children, increasing health risks.

Alternatives to arsenic-treated lumber have existed for years.

“We’re probably 50 percent converted already, but it is more expensive.” said Richard Giguere, vice president of Ware-Butler.

Giguere and Masse pegged the average cost increase at about 20 percent. Other than its cost, consumers should notice little difference in the lumber, Masse said.

Dealers say arsenic-treated lumber can still be used safely for many purposes, and assessments of its danger to humans vary widely.

“How large those potential risks are is uncertain, but various state and federal agencies have made estimates that generally fall in the range, the fairly broad range, of one in 1,000 to one in 10,000,” Smith said.