Like a cup of arsenic? Oh, you've already got some.

Arsenic levels vary widely, but they are dangerously high in much of the country.

by Illustration: Jason Lee

ARSENIC BY AREA
Arsenic levels vary widely, but as this map shows, they are dangerously high in much of the country.
Illustration: Jason Lee

Arsenic is one of history's most infamous poisons. The Roman Emperor Nero used it to murder his rival to the throne, and some theorists hold that the deposed Napoleon Bonaparte was betrayed with a dose from trusted deputies. Yet, many Americans unwittingly drink toxic quantities of the stuff right from their taps.

Arsenic is also a chemical element that occurs naturally in rocks and soils all over the world. It enters into water supplies when the minerals in these formations dissolve, or when they are released by mining or other industry. The first arsenic standard for drinking water was set in 1942 at 50 parts per billion (ppb), or five teaspoons per 1.3 million gallons of water. But that was before its potency was widely understood. According to a September 2001 study by the National Academy of Sciences, even trace amounts can cause bladder and lung cancer. Other studies have linked arsenic to diabetes, respiratory and cardiovascular ailments, and birth defects. The Environmental Protection Agency -- criticized for its failure to act sooner -- has finally reduced the standard to 10 ppb. Even at that level, the lifetime cancer risk from arsenic is 30 times greater than that for any other carcinogen regulated by the EPA. "But if you lowered the limit to 3 or 5 ppb," says Skip Wolfe, of Kinetico, a water treatment company in Newbury, Ohio, "the cost would rise exponentially because so many more communities would be affected" (see map).

Still, the new limits will keep companies like Kinetico busy. Since only a handful of municipal water supplies exceeded the old limit, relatively few reduction systems are in place. More than 4,000 communities will now have to invest in some sort of removal technology (see chart). But many will take their time since, as Wolfe points out, "they have until 2006 to get their ducks in a row." Owners of private wells may also want to have their water tested. EPA water resources expert Thomas Sorg estimates tens of thousands of homeowners may have too much arsenic in their wells "and many don't even know it."

THE POISON POLICE

Communities and homeowners with private wells must choose from four basic methods of removing arsenic.

Co-Precipitation

How it works: Iron, which bonds to arsenic, is added to water. Resulting particles settle or
are removed.

Pros: Extremely reliable; rarely gets mucked-up by other contaminants, as other systems do.

Cons: Produces an arsenic-laced sludge. Chemicals must be added
to system on a regular basis.

Adsorptive Processes

How it works: Usually a bed of iron or aluminum. As water passes through, arsenic adheres to
surface.

Pros: Bed can either be thrown away or cleaned with solvents and reused.

Cons: Cleaning produces an arsenic-laced sludge. Performance depends on pH levels.

Membrane Filtration

How it works: Arsenic is rejected as water passes through
a membrane.

Pros: Low space requirement. Method also removes other contaminants.

Cons: As much as 20 percent of water is wasted along with arsenic.

Ion Exchange

How it works: Synthetic resin exchanges chloride for arsenic in treated water.

Pros: Tried and true technology has proven itself as a home water
softener.

Cons: Must be cleaned frequently. Chloride produces brine waste. Certain compounds can tie up system.