WASHINGTON (AP) -- Far fewer children are showing high levels of lead in their blood or the effects of secondhand smoke, a government report has found -- but childhood asthma rates are doubling.

The Environmental Protection Agency report published Monday also found that one of every dozen women of childbearing age has blood mercury levels that could hinder brain development in a fetus.

The EPA report is the agency's second comprehensive look at the environmental hazards to children's health.

The sharpest drop was in the number of children with elevated levels of lead in their blood. There were 4.7 million in 1978, and about 300,000 in 2000, the report says.

It attributed most of that success to the phaseout of lead in gasoline between 1973 and 1995 and the reduction in the number of homes with lead-based paint from 64 million in 1990 to 38 million in 2000.

The number of children whose blood levels showed effects from second hand smoke declined by about one-fifth to one-half between 1988 and 2000, depending on their levels of exposure. Those figures are obtained by tracking the amount of cotinine, a breakdown product of nicotine in blood.

EPA Administrator Christie Whitman said aggressive government intervention both those areas had made "great strides to improve the environment for children where they live, learn and play."

The percentage of children getting asthma has doubled in two decades, the report said, rising from 3.6 percent in 1980 to 8.7 percent, or 6.3 million children by 2001.

Researchers don't know exactly why asthma is increasing among children, but a number of factors in air quality, both outdoors and indoors, have been studied.

Those range from exposure to dust mites, cockroaches and pesticides to tobacco smoke, ozone and soot. EPA officials are intent on examining the role of indoor air pollutants, especially since there have been some modest improvements since 1990 in lessening the number of children exposed to outdoor air pollutants.

About 5 million women - or 8 percent of those at the childbearing ages of 16 to 49 - had at least 5.8 parts per billion of mercury in their blood as of 2000, the report says. EPA officials said this is the first time this kind of data has been measured.

EPA has found that children born to women with blood concentrations of mercury above 5.8 parts per billion are at some risk of adverse health effects, including reduced developmental IQ and problems with motor skills such as eye-hand coordination.

Mercury, a naturally occurring metal, is a persistent pollutant that accumulates in fish and becomes more concentrated as it moves up the food chain. The three major sources for mercury emissions have been power plants, municipal waste and medical waste incinerators.

EPA has regulated mercury deposited in water and air from municipal waste and medical waste incinerators since the late 1990s. A 90 percent reduction in the levels emitted from each of those sources is another agency success, spokesman Joe Martyak said.

Regulations for mercury emitted from coal-fired power plants are due to be completed over the next two years and scheduled to take effect by 2007.

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