Lead, Your Child’s Brain and Our Future

The generations coming after us are going to need all the brains they can get to manage the crises that we’ve failed to manage. And, low-level lead exposure to young children has been associated with decrements in cognitive performance. It’s not something like global climate change, where we now have less than a decade to reduce greenhouse gas emissions to avert the worst effects of the temperature increases. But childhood exposure to neurobehavioral toxicants such as lead is also a situation we should take care of sooner rather than later. Many other toxic effects, chemical carcinogenicity included, fade into insignificance next to the vision of a generation of low intellectual performers in a steadily more complex, challenging and hazardous world.

With that scenario in mind, there’s reason to be concerned about a study published by investigators at Duke University, and currently in press in Environmental Health Perspectives. It examined the relationships between blood-lead surveillance data and educational performance of 4th graders. Children in several counties in North Carolina were tested for blood-lead levels at ages ranging from 0 to 5 years. Later, the test scores from standardized testing administered at the end of 3rd grade for the same group of kids were compared with blood-lead test results. The study results were a bit surprising. The investigators concluded that discernable effects on test scores occurred with as little as 2 ug/dL blood lead (micrograms of lead per deciliter of blood). A blood-lead level of 5 ug/dL was associated with significant declines in test scores. In making sense of these results, keep in mind that the Centers for Disease Control intervention level (the level at which the local health department takes action to reduce lead exposure) is 10 ug/dL.

This is a consistent message with the CDC’s most recent report on childhood lead exposure, which also concludes that, that while some uncertainty still remains, the overall weight of available evidence supports an inverse (negative) association between blood lead levels less than 10 μg/dL and the cognitive function of children. The reason this is an issue is that, while a lot of progress has been made in reducing lead exposures, there are still a lot of children in the U.S. with blood-lead levels between 3 and 5 ug/dL (levels that the Duke investigators identified as levels of concern for educational performance).

Not everyone is convinced about the importance of the lead exposure-childhood cognitive effects relationship, particularly in Europe. A recent paper by experts in the UK concluded that efforts to minimize childhood exposure, while important, need to be seen in perspective. They state that the magnitude of the lead-IQ dose-response relationship is small on a population basis and should be set against the far greater combined effect of socioeconomic status and quality of parental care.

It has been argued that, instead of "chasing after an ever-receding lead threshold," attention and funds should be focused on "the more complex social ills that are associated with continued lead exposure in a small segment of the population" (Gee and McKay 2002). Current lead exposure accounts for a very small amount of variance in cognitive ability (1-4%), whereas covariates such as social and parenting factors account for 40% or more (Weiss 2000).

Whatever. Elevated lead exposures go along with low socioeconomic status and substandard housing, which means these need to be treated and addressed holistically as a social problem, rather than simply as a reduction in lead exposure. Better housing would be a start. How about subsidized day care and living minimum wage, while we’re at it? It’s probably going to be cheaper in the long run than remedial education and jails.