A quick look at Blood Lead Concentrations Less than 10 Micrograms per Deciliter and Child Intelligence at 6 Years of Age by Todd A. Jusko, Charles R. Henderson, Jr., Bruce P. Lanphear et al., published online in Environmental Health Perspectives.

The current CDC definition of elevated blood lead in a child is 10 micrograms of lead per deciliter of blood (written as 10 μg/dL). However, there is increasingly compelling evidence that lower blood lead levels are associated with decreased performance on intelligence testing. At the same time, it has just been reported that the EPA has just rejected the advice of scientific staff and an advisory committee to strengthen its environmental lead exposure standard, because of the deleterious effects of low level lead exposure. The study is still more evidence that lead remains a threat to children, even at levels previously thought to be safe, and that a stronger standard is needed.

In this study, a group of approximately 200 children were followed starting at the age of 6 months, with their blood lead measured 8 times by each child reached 6 years old. The findings, adjusted for maternal IQ and other potential confounding factors, are troubling. Children with lifetime average concentrations between 5 and 9.9 μg/dL (children who would not be considered as having elevated blood leads under current CDC definition) scored 4.9 points lower on the “Full-Scale IQ” test, compared with children who had lifetime average blood lead concentrations below 5 μg/dL.

This study is not the first study finding a measurable effect below 10 μg/dL (see here on the same cohort and here, for example) and is unlikely to be the last. Why hasn’t the CDC lowered the screening level from 10 to, perhaps, 5 μg/dL?

In 2001, Senator Jean Carnahan (D-MO) asked the CDC in 2001 to do just that – lower the threshold to 5 μg/dL. At the time, the head of the CDC division in charge indicated that the agency would probably make the change. Soon after, however, the CDC’s advisory committee on Childhood Lead Poisoning Prevention was given some new members, one of the first of the federal advisory committees that was “stacked” by the Bush Administration. Among those disqualified from serving was Dr. Bruce Lanphear (of the Cincinnati Children’s Hospital Medical Center, one of the authors of this study). The replacement nominees included several scientists with close ties to the lead industry.

The CDC’s now out-of-date level is very significant because EPA is using it to support the agency’s refusal to strengthen the environmental lead exposure standard. According to InsideEPA’s Clean Air Report (subscription only).

EPA’s upcoming proposal to revise the national ambient air quality standard (NAAQS) for lead rejects recommendations from agency staff and outside advisers to acknowledge health risks from the metal at levels lower than the “action” levels identified by the CDC, a move that will likely result in the agency proposing to either maintain or weaken the current lead NAAQS, EPA and other sources say.

While many experts have argued for tightening the lead NAAQS based on studies that raise concerns about blood lead concentrations below the CDC’s current action level of 10 micrograms per deciliter (10 ug/dL), EPA’s policy office is insisting that any revision be based on the CDC level, a decision that appears likely to result in EPA maintaining or weakening the current NAAQS, the sources say.

The agency’s Office of Policy, Economics & Innovation (OPEI) does not intend to pursue the recommendation by air office staff and the independent Clean Air Scientific Advisory Committee (CASAC) that a new NAAQS be based on a lower blood lead “action” level than the CDC 10 ug/dL level of concern for children, an OPEI source says. OPEI, which is part of the administrator’s office, considers scientific and policy issues and reviews program office proposals before publication to ensure consistency with agency priorities and relevant statutes.

Eliminating lead in gasoline has been one of public health’s shining acheivements; the resulting reduction in lead exposure has resulted in a sizable increase in IQ levels in children throughout the country, with accompanying benefits. But the public health community must not rest on our laurels. It is high time to recognize that current lead exposure levels are not safe and take appropriate action.

Citation: Jusko TA, Henderson CR, Lanphear BP, et al., Blood Lead Concentrations Less than 10 Micrograms per Deciliter and Child Intelligence at 6 Years of Age published online in Environ Health Perspect doi:10.1289/ehp.10424 (available at http://dx.doi.org/) online 20 November 2007.