@boomzilla said:
@aliquot said:I read the rest of the article, the idea is to lower the lead-blood-level threshold for action to below the "Shit, this kid has lead poisoning" level, so that public health officials can take action before the kids actually get lead poisoning.
I'll give you the benefit of the doubt, and assume you just didn't read closely enough instead of innumeracy, and will inform you that the current standard, 10 is well below the threshold for poisoning, which is 45. This is in decimal numbers, BTW, so the current regulatory threshold has a 350% buffer before the clinical problem of poisoning is reached.
You are mixing up two different things here. Acute clinical lead poisoning != the only bad effect lead has on children. Here's the quote you're referencing in the article: @NYT said:
Actual lead poisoning, he said, is defined as blood levels above 45
micrograms per deciliter of blood (µg/dL). At that level in young children, he
said, “their life is at risk, they need to be seen clinically, and
interventions absolutely need to be taken immediately."
What he's calling "actual lead poisoning" means your blood level is so high that the lead has systemic effects - and if high enough, can actually kill you. At 70-100 µg/dL kids can have comas and seizures. At 45 µg/dL you can get anemia, porphyria-like symptoms, lethargy, gross neurological effects and so on. 6 weeks of 45 µg/dL and you will get "lead lines" in your bones which show up on X-ray. IANAD but it appears 45 µg/dL is the clinical threshold for "severe" lead exposure meaning you need chelation therapy to get the lead out of your blood.
So that's what the 45 µg/dL number refers to. But, children exposed to much lower levels of lead have lower IQs and higher prevalence of ADD. These neurological effects are irreversible, so when you take the lead away the kids don't get smarter. The 10 µg/dL threshold in children is about this, not about acute ie "actual lead poisoning." The reason the CDC has changed the threshold from 10 µg/dL to 5 µg/dL is that a lot of new science has come out showing neurological effects in children from blood lead levels < 10 µg/dL.
If you're actually interested, here's the report from the advisory committee that recommended the lower threshold: http://www.cdc.gov/nceh/lead/ACCLPP/Final_Document_010412.pdf It summarises the more recent science showing permanent, irreversible damage to children from blood lead levels < 10 µg/dL.
@boomzilla said:
@aliquot said:Preempting lead poisoning in kids doesn't seem like a waste of money to me.
So, at what level of lead does it become "poisoning?" It's nearly as much of a cliche in toxicology as correlation/causation is in statistics, but "the dose makes the poison." How much will it cost to reduce the lead from minuscule amounts to microscopic amounts? What are the benefits?
I skimmed the report from the advisory committee and learned that even with blood level 1 ug/dL - 4 ug/dL there is a measurable drop in IQ of about 3-4 points. Definitely something "unnoticeable" in one child, only noticeable in a large study with a control group. At 10 µg/dL the drop is about 5 IQ points. And a population drop of 5-10 IQ points can make a big difference in the number of people who are moderately retarded.
Most parents whose kids have BLL (blood lead level) of 5-10 µg/dL will have no idea because the symptoms are subclinical. Kids with 10 µg/dL BLL won't be anemic, have gastrointestinal problems or seizures or gray skin, but will be on average 5 IQ points stupider and 1cm shorter. If their parents knew they had elevated blood lead levels, they could do something about it before their kids grew up a little stupider and a little shorter. The article links to a blog post that explains how lowering the threshold to 5 µg/dL will result in more screening, more lead abatement from property owners, more family lead education and follow-up testing.
What's the cost to society of many people being a little bit stupider,
and a big difference in the number who meet the cutoff for moderate
retardation? I don't even begin to know how to calculate that.
tl;dr : The CDC lowered the threshold from 10 µg/dL to 5 µg/dL because there's new science showing irreversible cognitive effects from childhood blood lead levels <10 µg/dL. 5-10 µg/dL of lead in the blood won't make a kid sick the way 45 µg/dL will, but it will make the kid stupider.