The state Bureau of Health is testing nearly 1,000 wells for arsenic in an effort to determine the levels of the element in residents’ drinking water. The statewide tests began last month amid growing concern over the levels of arsenic in water. Arsenic can cause gastrointestinal problems, bladder and lung cancer, and other illnesses.

The testing also comes at a time when the federal Environmental Protection Agency is reconsidering rules established last year to lower the acceptable level of arsenic in public drinking water from 50 parts per billion to 10 parts per billion.

Significant concentrations of arsenic have been found over the past decade in Northport, Owls Head, Buxton and Hollis.

It also was found in Standish, where about half of the wells tested by homeowners in recent months showed arsenic levels above 10 parts per billion.

State Bureau of Health scientists recommend that homeowners take action if their water tests above that level. The state cannot force individual homeowners to lower arsenic in their own wells.

“Compared to other public drinking water risks, few other [chemicals] pose such a high risk,” said Andrew Smith, toxicologist for the Bureau of Health.

People who drink water with high amounts of arsenic have an increased risk of getting cancer.

Dealing with arsenic in the water is relatively easy. Bottled water or a treatment filter on the kitchen sink will take care of the problem. And arsenic in the body dissipates quickly, so there is usually no long-term damage when people stop drinking tainted water.

Smith said well owners should routinely test their wells because neighborhoods can have vastly different levels of arsenic. Similarly, “clusters” of wells that have all tested for high levels of arsenic have been found throughout the state.

Smith estimated that anywhere from 2 percent to 15 percent of wells in Maine have arsenic levels above 50 parts per billion. Between 15 percent and 30 percent of wells are above 10 parts per billion, he estimated.

Recently, President Bush angered environmental advocates when his administration announced that the EPA would reconsider the stricter arsenic standard for public water.