"Safe" Blood Lead Level?

Children's Environmental Health Network Listserv  9feb01

Question

A recent article (5/20/00) by my favorite environmental journalist, Dan Jones of the Hartford Courant, mentioned some new research on lead toxicity standards, which I'm interested in pursuing further. Specifically, he wrote,

"In a study of nearly 5,000 children, Dr. Bruce Lanphear, associate professor of pediatric medicine at Children's Hospital Medical Center in Cincinnati, found impairments in math and reading skills and short term-memory deficiencies, even when lead levels were well within the acceptable limit--10 micrograms per deciliters of blood.

"'Even though we think about 10 micrograms as a magic number, it really isn't, and we're finding adverse effects down to 2.5 mg/dl, said Lanphear, who presented his findings at a recent meeting of the Pediatric Academic Societies and the American Academy of Pediatrics."

 I'm not able to find a citation for this study on medline, and before I attempt to track down Dr. Lanphear, I thought I'd just ask if anyone knew whether or not this study is forthcoming in a peer-reviewed journal.

Also, I'm wondering how his claims--if accurately represented above--are regarded in the lead community:  have other researchers replicated adverse effects down to 2.5?  Does this represent a paradigm shift?  Can someone place this new study in a context of the current thinking of lead toxicity?

One last question:  I'm doing some writing for new mothers on pre and post natal lead exposures.  My own daughter, who was born in Boston in 1998 and spent the first months of her life in Somerville (where Needleman conducted his groundbreaking 1979 study) had a blood lead of 6 when she was 9 months old.  She was not yet crawling and had spent no time on the floor.  Although we lived in a 100-year-old apartment building which undoubtedly had lead paint under the many layers of interior and exterior paint, a home lead test kit showed no lead in our dusty corners, walls, cupboards, or floors.  Can I therefore assume that her blood leads mostly represent prenatal exposures, probably from lead reserves released from my bones?  (I was born in 1959.)  After we moved to Ithaca into a lead-free log cabin, her blood leads dropped to less than 3 (at 15 mo. old).  She continued to breastfeed during this interval.

Answer

To address the comment attributed to Dr. Lanphear: "Even though we think about 10 micrograms as a magic number, it really isn't, and we're finding adverse effects down to 2.5 mg/dl."

It may be that part of the difficulty in defining a " safe" blood lead level (BLL) below which health effects do not occur, stems from the use of blood lead itself as an indicator of toxicity. BLLs will reflect only recent exposures (within 30-60 days). A child who has been chronically exposed (>365 days) may not have elevated BLLs but may have an elevated body burden of lead (as evidenced by elevated bone lead levels) and may in fact be showing signs of neurotoxicity i.e. developmental delays at "low" blood lead levels. See for example: Rosen JF, Crocetti AF, Balbi K, Balbi J, et al. Bone lead content assessed by L-line x-ray fluorescence in lead-exposed and non-lead exposed suburban populations in the United States. Proc. National Academy of Sciences 1993;90: 2789-2792.

The Agency for Toxic Substances and Disease Registry also notes that: "[Blood lead] concentration reflect the absorbed dose of lead. However, the interpretation of [blood lead] data depends on a knowledge of the past history of exposure to lead. This is because in the body, bone constitutes the major lead sink and this results in lead having a long body half-life. Thus, in the absence of intense exposure to lead for a considerable period up to its body half-life, the [blood lead] concentrations reflect recent lead exposures. "(Agency for Toxic Substances and Disease Registry. Toxicological Profile for Lead (Update). U.S. Department of Health and Human Services. 1998; p.22)

Animal studies have also demonstrated that blood lead levels do not properly reflect amounts of lead that may be stored in brain tissue, especially in instances of chronic low level exposure. (Nihei MK, Desmond NL, McGlothan JL, Kuhlmann AC and Guilarte TR. N-methyl-D-aspartate receptor subunit changes are associated with lead-induced deficits of long-term potentiation and spatial learning. Neuroscience 2000; 99(2):233-242.)

Pertaining to lead sources for your daughter, have you considered tapwater lead levels? A study commissioned by the CMHC (the Canadian version of HUD) found that "[the] primary predictors of raised blood lead levels...was resident's age, household water lead level, and lead in paint...[however, t]he primary residential source was confirmed to be lead in household water."Source: Residential Sources of Lead Prepared by Metro Health Services Inc. Principal consultant: Richard E. Scott. Prepared for Residential Division of Canada Mortgage and Housing Corporation, Ottawa: CMHC; 1995.  http://www.cmhc-schl.gc.ca/cmhc.html  The plumbing in a 100-year-old apartment building would undoubtedly be contributing some lead to drinking water.

Hope this is helpful.

Kelly O'Grady R.N.
Lead Environmental Awareness and Detection (L.E.A.D.)
www.webhart.net/lead  
219 Welland St.,
Pembroke, ON
CANADA K8A 5Y5
(613) Tel:735-0717

• EPA Lead Program http://www.epa.gov/ebtpages/polairpolead.html

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From: "Kelly and Michael" <lead@webhart.net> To: "Sandra Steingraber" <ss235@cornell.edu>; <cehnlist@cehn.org> Subject: [CEHNList] lead question