Run by

The LEAD Group Inc
The Lead Education and Abatement Design Group
Working to eliminate lead poisoning globally and to protect the
environment from lead in all its uses: past, current and new uses
ABN 25 819 463 114
Australians! Take action
today. Is lead harming
you & your kids? Buy low
cost, NATA accredited
laboratory lead test kits
Sample your dust,
soil, water, paint, toys,
jewellery, ceramics
what's new 

Water Lead test Kits

Proceeds from our DIY Home Lead Assessment kit sales go towards the
Keeping Australian Lead Out of Leaded Petrol Initiative.

About Us | bell system lead poisoning | Contact Us | Council LEAD Project | egroups | Library - Fact Sheets | Home Page | Media Releases
| Q & A | Referral lists | Reports | Site Map | Slide Shows - Films | Subscription | Useful Links |  Search this Site

PDF of this file

Exposure Assessment: Lead Neurotoxicity

Is the Center for Disease Control's goal to reduce lead below 10 µg/dl blood in all children younger than 72 months by 2010, good enough?

Thomas F. Schrager, Ph.D.

[Source:         [LID 8777]

Blood lead threshold levels have been decidedly downward over the past forty years. While it may be possible that the bottom has been reached or that new research might at some point reverse the trend--something that does happen with other chemicals, although rarely--recent evidence suggests that the direction of the trend for lead will continue. In part this is due to better data at lower concentrations of lead, simply showing or confirming what has been suggested for a long time by insufficient data. And in part this is due to an appreciation and ability to test much more subtle effects of lead toxicity.

The results of the jury verdict in Rhode Island that held paint manufacturers responsible for lead paint that remains in homes and the toxic consequences of this situation, come at a time of growing understanding of the more subtle toxic effects of lead in the neurological development of children; that is, that (much) lower blood lead (BPb) than previously shown or considered, can be toxic and over a wider range of adverse affects. The rapid change in which significantly lower lead toxicity and the stakes involved has been recognized is reflected in the speed of change in acceptable threshold levels. The 1990 decision by the U.S. Department of Health and Human Services to eliminate all BPb > 25 µg/dl in children 6 months through 5 years of age by 2000 (Healthy People 2000) was followed in 1991 by a reduction in that 25 µg/dl threshold of concern to 10 µg/dl by the Centers for Disease Control (CDC 1991). By the late 1990’s a new, Healthy People 2010 goal was set to eliminate all BPb > 10 µg/dl (Myer et al 2003; US Dept HHS 2000).

By implementing these different thresholds and goals, the proportion of children at-risk (BPb > 10 µg/dl) has been reduced during the past thirty years from approximately 88 percent to 2.2 percent (NHANES 2000), an obviously very significant accomplishment in public health efforts to eliminate child lead poisoning. Nevertheless, CDC estimates that the 2.2 percent figure translates into more than four hundred thousand children with BPb > 10 µg/dl (NHANES 2000), and is a nationwide average; inner city and/or low socioeconomic areas often have much higher proportions of children with BPb exceeding 10 µg/dl, typically 8-10 percent of children and in some areas as high as twenty percent. Lead poisoning clearly remains a major problem in these areas, the very places that can least afford further compromise of intellectual functioning, due to negative socioeconomic circumstances and lack of early childhood stimulation.

Also, associations between BPb and intellectual functioning are typically based on population averages; neuropsychological testing of individuals, especially those with borderline intellectual functioning, shows widely varying impacts from individual to individual of even a few-point decrement in IQ (Dietrich 1993). And a few point decrement in intellectual functioning, among hundreds of thousands of children with borderline intellectual functioning to start with, can produce enormous economic and social impacts (Fulton et al 1987).

A ‘Safe’ Threshold for Lead Toxicity?

Further extending this trend, additional data and new analysis of existing data support a growing scientific consensus that a threshold for lead neurotoxicity in fetuses and young children does not exist (WHO 1995; CDC 2003); CDC stated in a consensus report that ‘a threshold for harmful effects of lead remains unknown’ (Myer et al 2003). And following the release of the comprehensive ‘Third National Report on Exposure to Chemicals in Humans’ (CDC 2005), Jim Pirkle, deputy director of CDC’s Environmental Health Lab, stated unequivocally that a safe blood lead level in children simply does not exist.

The progressive reduction over time in the toxic threshold of lead ( a similar trend seen with most other chemicals) results from accumulation of data, improved understanding of target tissue injury, and more sophisticated tools and methodology to measure adverse toxic effects. The ‘safe’ threshold for lead has been revised downward six-fold during the past thirty years, from 60 µg/dl prior to 1971, 40 µg/dl until 1978, 30 µg/dl until 1985, and 25 µg/dl from 1985 until 1991 when the threshold was changed to the present < 10 µg/dl level (CDC 1975; CDC 1985; CDC 1991). Each reduction in threshold leads to greater focus on BPb toxicity at lower levels and, with that, more accumulated data at those lower levels, allowing verification of a reduced toxicity threshold.

Increasingly, the 10 µg/dl ‘threshold’ for lead is seen to reflect a ‘threshold’ of reliable data rather than a threshold of toxicity; that is, until recently insufficient data existed to verify lower toxicity, rather than sufficient data showing no toxicity at lower levels. This distinction is often the case and just as often is not made clear, leading to misinterpretation of data and toxicity. One resultant problem has been insufficient monitoring of children from infancy through five years of age or more—generally believed the critical window of significant and lasting neurological damage—so it has been difficult to know whether observed neurological effects at sub-10 µg/dl BPb concentrations actually reflected toxicity at those levels or simply reflected missed monitoring of periodic spikes of BPb above10 µg/dl during the critical exposure period.

Lanphear et al (2005) conducted a pooled analysis of 1333 children from seven studies, which produced sufficient numbers of children whose BPb had been closely monitored during the critical early childhood period and whose BPb had not exceeded certain levels at any time. The Lanphear study found two such groups: those whose BPb did not exceed 10 µg/dl and those that did not exceed 7.5 µg/dl, allowing these two distinct BPb groups to be compared with those with BPb ranging from 10 µg/dl to 30 µg/dl from shortly after birth to five years of age. IQ was also measured during this time period. They found that increases of BPb from 2.4 to 10 µg/dl caused a much greater decrement in IQ score than increases in BPb from 10 to 20 µg/dl, or from 20 to 30 µg/dl. These results confirmed an earlier study by Canfield et al (2003), that tracked BPb from infancy through five years of age, with more than half having BPb that never reached or exceeded 10 µg/dl. Canfield found that BPb increases from 1 µg/dl to 10 µg/dl resulted in a decrement of 7.4 IQ points, compared to decrements of 4.6 IQ points for each additional 10 µg/dl increase in BPb above10 µg/dl. A steeper dose response curve of BPb below, as opposed to above, 10 µg/dl, was also demonstrated in a study by Schwartz (1994).

A reanalysis of a Boston cohort by Bellinger and Needleman (2003), prompted by the Canfield results, found 48 children whose BPb had been closely monitored in early childhood and had never reached or exceeded 10 µg/dl, and they too found a steeper drop in IQ versus increases in BPb below 10 µg/dl, as compared to increases above that level. The Bellinger and Needleman reanalysis was also important because this cohort included many middle and upper middle income students. One of the questions about the steeper sub 10 µg/dl dose-adverse effect curves was whether the (detrimental) influence of other confounding factors, such as maternal IQ, stimulation of the home environment in early childhood or absence of other early educational opportunities, simply became more pronounced and apparent as the affects of very low BPb levels were reduced. Assuming such effect was solely due to BPb would create a seemingly disproportionate toxic effect of lead on IQ at those (very low) levels. The Bellinger and Needleman study, as well as other similar sub-10 µg/dl studies, suggests that these confounders were not the cause for the steeper dose response curve.

Rothenberg and Rothenberg (2005) extended these findings by applying a log linear model to these dose response relationships, rather than the usual linear model and found the log linear model fit the data better. The linear model emphasizes an absolute effect of BPb dose on toxicity, whereas a log linear model emphasizes a proportionate effect. For example, a linear model predicts that a 10 µg/dl increase in BPb (from 10 µg/dl to 20 µg/dl) exerts twice the toxicity as would a 5 µg/dl increase (from 5 µg/dl to 10 µg/dl), whereas the log linear model would predict a more proportionate increase in toxicity in each case.

The actual dose response curves fit the latter model much better than the former, and this has a number of implications. Such model not only predicts that a significant portion of low level lead toxicity occurs below 10 µg/dl, as reflected in the above studies, rather than above 10 µg/dl, but that the economic costs associated with intellectual, behavioral and other neurological deficits are more than twice previously calculated (Canfield 2003).

Lead neurotoxicity in young children affects not only intellectual development but other behavioral and social parameters, which can also greatly impact one’s success in life and the social costs of managing these problems. Needleman (2002) showed that bone lead (the lead reservoir) in young males was correlated with increased criminal behavior, anti social attitudes and other forms of juvenile delinquency. Dietrich et al (2001) showed similar effects on juvenile delinquency.

A study by Nevin (2000) shows a correlation between use of lead-based paint, as well as leaded gasoline, and both unwed pregnancy and criminality, including murder, as far back as the early 1900’s. This study also showed a steeper dose relationship between BPb below 10 µg/dl and IQ deficits, compared to above 10 µg/dl, and showed a correlation between IQ deficits and social/behavioral problems, suggesting a significant effect of lead on social behavior at very low BPb.

Whereas lead toxicity is expressed and observed early, at the time of exposure, in causing apparently irreversible decrements in intellectual and social functioning, experiments by Basha et al (2005) (suggest latent neurotoxic effect from early, transient lead exposure. Rats dosed with lead during the first twenty days of life exhibited elevated BPb, characteristic of lead poisoning, which subsequently returned to normal post dosing. During the dosing period, APP mRNA also showed increased activity during the neonatal period of increased BPb, which also returned to normal. But in old age APP mRNA again became active, accompanied by excessive amounts of APP (B-amyloid precursor protein), the protein from which B-amyloid deposits are derived in the brain. These deposits are characteristics of brains in Alzheimer’s patients. In older rats not dosed in early life but dosed for two months in old age, no such increase in APP m-RNA, APP or B-amyloid was found, suggesting that early lead exposure can not only produce permanent tissue damage with significant life long effects, but program alterations in gene expression which can cause significant effects later in life.

Beyond these neurotoxic effects lead is also implicated in cardiovascular disease, renal damage and dental caries. Taken together, these early, life long adverse effects of lead exposure, at likely very low levels, underlines the importance and implications of the Rhode Island jury verdict and repercussions it may have on communities throughout the country. Although the latest data remains to be verified, the trend is clearly in one direction and the consequences, both on the individual and on society are so great, that erring on the side of prevention seems the prudent course.


Basha MR, Wei W, Bakheet SA, Benitez N, Siddiqi HK, Ge YW, Lahiri DK, Zawia NH. (2005) J Neurosci. 25(4):823-9.

Bellinger DC and Needleman HL (2003) N Engl J Med 349:500-2.

Canfield RL, Henderson CR Jr, Cory-Slechta DA, Cox C, Jusko TA, Lanphear BP. (2003) N Engl J Med 348:1517-26.

CDC (1975) Statement by CDC. Atlanta, GA US HEW, CDC

CDC (1985) Statement by CDC. Atlanta, GA US HEW, CDC

CDC (1991) Preventing Lead Poisoning in Young Children. Atlanta, GA:Centers for Disease Control.

CDC (2005) Third National Report on Human Exposure to Environmental Chemicals. US HHS, CDC, Alanta, Ga. (

Dietrich KN, Berger OG, Succop PA, Hammond PB, Bornschein RL(1993) Neurotoxicol Teratol. 15(1):37-44

Dietrich KN, Ris MD, Succop PA, Berger OG, Bornschein RL. (2001) Early exposure to lead and juvenile delinquency. Neurotoxicol Teratol 23:511-518

Fulton M, Raab G, Thomson G, Laxen D, Hunter R, Hepburn W (1987) Lancet 1: 1221-1226.

Lanphear BP, Hornung R, Khoury J, Yolton K, Baghurst P, Bellinger DC, et al. (2005) Environ Health Perspect 113:894-899.

NHANES (2000) Third National Health and Nutrition Examination Survey, 1999-2000. Phase 3. CDC US DHH.

Needleman HL, McFarland C, Ness RB, Fienberg SE, Tobin MJ. (2002) Neurotoxicol Teratol 24: 711-717.

Nevin R (2000) Environ Res. 83(1):1-22.

Rothenberg SJ, Rothenberg JC (2005) Environ Health Perspect 113:1190-5.

Schwartz J (1994) Low-level lead exposure and children's IQ: a meta-analysis and search for a threshold. Environ Res 65(1):42-5.

PDF of this file

The LEAD Group Inc. Fact Sheet Index

NSW Lead Reference Centre and NSW Government Publications On this site

  1. About the Global Lead Advice and Support Service (GLASS)

  2. Main Sources of Lead

  3. How Would You Know If You or Your Child Was lead poisoned?

  4. Lead aware housekeeping

  5. Ceiling dust & lead poisoning

  6. Is your yard lead safe?

  7. Health Impacts of lead poisoning

  8. Rotary Questionnaire

  9. Lead poisoned Pets and Your Family

  10. Childhood Lead Poisoning Risk Factor Questionnaire

  11. Is Your Child Safe From Lead? - What Can You Do About Lead?

  12. Lead in Drinking Water in Australia

  13. Have We Really Resolved The Lead Issue?

  14. The Importance of the Availability of "Spot Tests" for Lead in Paint

  15. Pregnant or Planning a Pregnancy

  16. Breastfeeding and Lead

  17. Lead in breast milk

  18. Beware The Lead In Lead Lighting

  19. Renting and Lead

  20. What to do if you have too much lead in your tank water

  21. Lead Contamination in Stormwater

  22. Contamination At Shooting Ranges

  23. Banned: Leaded Wick Candles

  24. Lead, Ageing and Death

  25. Metal miniatures: How to minimise the risks of lead poisoning and contamination

  26. 7 Point Plan for the MANAGEMENT OF LEAD by Australian parents and carers

  27. Countries where Leaded Petrol is Possibly Still Sold for Road Use, As at 17th June 2011

  28. Lead Poisoning And The Brain - Cognitive Deficits And Mental Illness

  29. Facts and Firsts of Lead

  30. Lead mining royalties by state and territory

  31. Lead Mining Stewardship - Grey Lead and the Role of The LEAD Group

  32. Preventative Strategies of The LEAD Group

  33. What do Doctors need to do about Lead?

  34. A Naturopath's Experience Of Lead & People With Diagnosed Mental Illness

  35. Case File: Helping Manage Australian Lead in Petrol - How GLASS Works

  36. Glass Web & Service-Users, Experts & Volunteers, by Country; Countries with Leaded Petrol for Road Use & Worst Pollution

  37. Lead in ceiling dust

  38. Lead paint & ceiling dust management - how to do it lead-safely

  39. Esperance parliamentary inquiry follow-up factsheet: Where to from Here??

  40. Broken Hill lead miners factsheet 1893 with Note 20081015

  41. Helping a Doctor Help 35,000 Lead-Poisoned People Around the Lead Smelter at La Oroya in Peru
    Ayuda a un doctor que ayuda 35,000 personas envenenadas por plomo alrededor de la fundidora de plomo en la Oroya-Peru

  42. Fact sheet for Australian toy importers and traders

  43. Iron Nutrition & Lead Toxicity
    Informe de Acciones – Hierro y Plomo en la Nutrición

  44. Sanitarium-Are You getting Enough Iron

  45. Do-It-Yourself-Lead-Safe-Test-Kits-flyer

  46. Blood lead testing: who to test, when, and how to respond to the result

  47. Dangers of a blood lead level above 2 µg/dL and below 10 µg/dL to both adults and children

  48. Lead Exposure & Alzheimer’s Disease: Is There A Link?

  49. In CHINA - Blood lead testing: who to test, when, and how to respond to the result

  50. Why you should have your ceiling dust removed before you take advantage of the Australian government's Energy Efficient Homes Package: Insulation Program

  51. Alperstein et al Lead Alert - A Guide For Health Professionals 1994

  52. Ceiling Dust WorkCover Guide Lee Schreiber Final Nov 1999

  53. What can I do about climate change AND lead?

  54. The Need for Expert Clinical Assessments in Diagnosis Of Heavy Metal Poisoning

  55. Why you should have your ceiling dust removed before you have insulation installed

  56. Thirty Thought-Starters on Ceiling Void Dust in Homes

  57. Pectin: Panacea for both lead poisoning and lead contamination

  58. Nutrients that reduce lead poisoning June 2010

  59. Lead poisoning and menopause

  60. Fact sheet For Schoolkids From Professor Knowlead About Lead

  61. Prevention of Exposure to Lead at Work in Indonesia

  62. Mencegah kontak dengan timbal di tempat kerja di Indonesia

  63. How to Protect Your Family from Lead in Indonesia

  64. Bagaimana melindungi keluargamu dari timbal di Indonesia

  65. Cigarette Smoking & Lead Toxicity
     صحيفة معلومات: التدخين والتسمم بالرصاص

  66. Medical Evaluation Questionnaire For Occupational Lead Exposure

  67. Dangers of a blood lead level above 2 µg/dL and below 10 µg/dL to children

  68. Dangers of a blood lead level above 2 µg/dL and below 10 µg/dL to adults

  69. Biosolids used as fertilizer in China and other countries

  70. What are the lead poisoning risks of a lead pellet, bullet or shot lodged in the body?

  71. Alcohol’s link to higher lead and iron levels

  72. USA Case Definition of Adult (including Occupational) & Child Elevated Blood Lead Levels (EBLL)

  73. Low Level Lead Exposure Harms Children - A Renewed Call for Primary Prevention

  74. Occupational Health & Safety Fact Sheet Dangers of lead for roofers

  75. Let’s Make Leaded Petrol History - Let’s Make Leaded Gasoline History

  76. Lead, Your Health & the Environment. Available in Arabic, Chinese, English, Korean, Macedonian, Spanish, Turkish and Vietnamese 

  77. Lead Safe Housekeeping

  78. Old Lead Paint

  79. Working safely with lead

  80. A Renovator's Guide To The Dangers Of Lead (Brochure 30 pages)

  81. A Guide For Health Care Professionals (Brochure 34 pages)

  82. A Guide To Keeping Your Family Safe From Lead (Brochure 20 pages)

  83. Lead Hazard Management In Children's Services (Brochure 15 pages)

  84. A Guide To Dealing With Soil That Might Be Lead-Contaminated

  85. Exposure Assessment: Lead Neurotoxicity - Is the Center for Disease Control's goal to reduce lead below 10 µg/dl blood in all children younger than 72 months by 2010, good enough?

  86. Foods for Lead Detox - Foods which Fight Lead Poisoning
    Alimentos para la Desintoxicación de Plomo - Alimentos que Luchan contra el Envenenamiento con Plomo

  87. Veganism - How do you obtain all the nutrients from a vegan diet that are important to lead exposed individuals?

  88. Blood Lead Challenge - Take the blood lead discovery and reporting challenge;
    El Desafío del Plomo en la Sangre - Descubra el nivel de plomo en la sangre y desafíe las estadisticas;
    Défi de Plomb dans le sang - Partez ŕ la découverte de plomb dans votre sang et informez nous:

About Us | bell system lead poisoning | Contact Us | Council LEAD Project | egroups | Library - Fact Sheets | Home Page | Media Releases
| Q & A | Referral lists | Reports | Site Map | Slide Shows - Films | Subscription | Useful Links |  Search this Site

Privacy Policy | Disclaimer

Visitor Number

Last Updated 14 March 2015
Copyright © The LEAD Group Inc. 1991- 2015
PO Box 161 Summer Hill NSW 2130 Australia
Phone: +61 2 9716 0014