The U.S. Environmental Protection Agency (EPA) is preparing to revise the national standard for airborne lead pollution, but differing scientific opinions among federal officials are further complicating a protracted rulemaking effort. The prevailing interpretation may have a significant impact on the agency's decision to tighten or weaken the standard.

EPA is developing its proposed revision for the National Ambient Air Quality Standard (NAAQS) for lead. Lead is one of six pollutants regulated by EPA's NAAQS program, which requires the agency to regularly evaluate and revise air quality standards and ensure federal regulations are fully protective of public health, regardless of their economic impact. The current standard for lead is 1.5 μg/m³ (micrograms per cubic meter), a weight to volume measure of lead concentration in the air.

According to EPA, "The major sources of lead emissions have historically been motor vehicles (such as cars and trucks) and industrial sources." According to the American Lung Association, "Exposure to lead occurs mainly through the inhalation of air and the ingestion of lead in food, water, soil, or dust." Lead exposure can lead to a variety of adverse health effects including organ damage and neurological impairment. Its effects are most pronounced in children.

Environmental scientists on EPA's staff are recommending a markedly tighter air quality standard for lead. In its Nov. 1 final Staff Paper, EPA's Office of Air Quality Planning and Standards found, "The overall body of evidence on lead health effects: Clearly calls into question the adequacy of the current standard; and provides strong support for consideration of a lead standard that would provide greater health protection for sensitive groups, especially for children." The staff paper recommends a range of levels from 0.2 μg/m³ to as low as 0.02 μg/m³.

Administrator Stephen Johnson will use the staff recommendations — along with the input of EPA advisory committees, public comment, and his own examination of the scientific evidence — when deciding on the standard.

However, statistics from the Centers for Disease Control and Prevention (CDC) — a federal body housed within the Department of Health and Human Services — are confounding the EPA staff recommendations. CDC establishes a "level of concern" for lead and other toxins. The current level of concern for lead is 10 μg/dL (micrograms per deciliter), a measure of lead concentration in the human bloodstream. Although CDC recognizes "recent studies suggest that adverse health effects exist in children at blood lead levels less than 10 μg/dL," the agency has not lowered the level of concern because it believes adequate evidence does not exist to properly identify a lower level.

If EPA abides by CDC's endorsement of a 10 μg/dL level of concern, there would be no need to tighten the air pollution standard to achieve that health outcome, experts say. However, if EPA were to endorse a lower blood lead level as protective of public health, it would be obligated to tighten the air quality standard in order to effect the lower concentration.

Policy analysts inside EPA's Office of Policy, Economics & Innovation (OPEI) are using CDC's numbers to chart a course in which the agency could weaken the standard. According to Inside EPA (subscription), OPEI is pushing EPA to endorse the CDC's blood lead level of concern of 10 μg/dL. If officials within OPEI are successful, EPA will likely propose a revision to the standard that is weaker than the current one.

A recent scientific study gives further credence to the EPA staff argument that the current standard is not sufficiently protective of public health. A study published in the journal Environmental Health Perspectives found children with blood lead levels between 5 μg/dL and 9.9 μg/dL scored lower on IQ tests than children with blood lead levels less than 5 μg/dL.

The study examined children between the ages of six months and six years. The authors concluded, "Children's intellectual functioning at 6 years of age is impaired by blood lead concentrations well below 10 μg/dL, the CDC definition of an elevated blood lead level."

Under the Clean Air Act, EPA must revise all NAAQS every five years. EPA set the current standard in 1978. EPA has not reviewed the national standard for lead since 1990. During the 1990 review, EPA decided a revision of the standard was unnecessary.

EPA began its current review of the NAAQS for lead after a federal court mandated the agency undertake the rulemaking. In September 2005, as a result of a lawsuit brought by the Missouri Coalition for the Environment, the U.S. District Court for the Eastern District of Missouri ordered EPA to begin a review of the lead standard and set out a timetable for the review.

EPA was expected to publish an Advanced Notice of Proposed Rulemaking (ANPRM) by the end of November but has yet to do so. EPA submitted the ANPRM to the White House Office of Information and Regulatory Affairs (OIRA) on Nov. 16. OIRA reviews and edits agency regulatory actions before the actions are released to the public. OIRA has not completed its review of the ANPRM, according to its database on review.

EPA has indicated it will propose a new standard for lead in March 2008 and make its final decision by September of that year.