ANSWER: 21 Jan 2008

Dear Sir,

Thanks for your email and I agree with you - it's good to have some figures on our website which put lead into perspective both for those people who already have an elevated blood lead level (or who know they had one in the past) and for those who seek to prevent lead poisoning in themselves and others.

Perhaps you could use the figures that you have put in your email as a start and then confirm them all and in the process add a reference or two (preferably from a peer-reviewed journal article but certainly a reference including title, author, webpage and date) for each figure, and then we can web-publish it for the benefit of others.

I find that the hardest concept to get across is how research is changing our concept of how much lead is too much.

The date of any research finding is all-important of course because, at any point in time, there is a prevailing view about how much lead in the blood is an acceptable or safe or no-harm level. Since about the 1980's, there's been, until recently, the assumption that when the blood lead level rises from zero to ten micrograms per decilitre, no harm is done. That's the period in which research found that if the average lifetime blood lead level for children up to the age of about four years (ie the blood lead level taken at 6 or 12 month intervals and then averaged) was 20 micrograms per decilitre (mcg/dL), then, compared with a child whose average blood lead level (BLL) was 10 mcg/dL, the child (or more correctly the population of such children in the study) would likely have 1-3 IQ points less. That is, it was quite a popular statement to say that for EACH increase of 10 mcg/dL in BLL above 10 mcg/dL, a child could lose 1-3 IQ points and the effect was linear. Summary of old finding: there's basically no harm done until the BLL reaches 10 µg/dL (as an average for the critical brain development period) and after that you lose 1-3 IQ points if the average gets to 20 mcg/dL and 2-6 IQ points if you average 30 mcg/dL etc.

The stunning research finding that has occurred since then, is that the effect is NOT linear and it does NOT begin at 10 mcg/dL. Indeed, by far the most IQ loss for any range of 10 mcg/dL occurs when the blood lead level is in what was previously regarded as the "safe" range - as Dr Balzer writes, "Canfield, et al have shown that children with a lead level of 10 mcg/dL have an IQ seven points lower than those with a lead level of 1 mcg/dL." This research has really only become possible now that in the US (where most such research is done) there is no longer lead in petrol. This public health policy has arguably been the one most responsible for increasing the population of young children (who can thus now be studied) with extremely low blood lead levels ie one mcg/dL and less.

I'm just waiting now for a population of lead workers to become available who have such low blood lead levels, so that they can be compared to "normal lead workers" (to see when they die and what of) which will likely bring about a drastic reduction in the acceptable blood lead level for workers. Your father could be forgiven for not protecting you from lead when his workplace was likely telling him at that time that a blood lead level of 50 mcg/dL (or even higher, depending on how old you are) was "safe". I look forward to hearing back from you and wish you all the best with your studies.

Yours Sincerely

Elizabeth O'Brien