Blood lead level

Blood lead level (BLL), is a measure of lead in the blood. It is often measured in micrograms of lead per deciliter of blood (μg/dL) especially in the United States; 5 µg/dL is equivalent to 0.24 micromoles per liter (µmol/L).[1]

The Centers for Disease Control changed its view on blood lead levels in 2012.[2] Because of "a growing body of studies concluding that blood lead levels (BLLs) lower than 10 μg/dL harm children",[3] with "irreversible"[4] effects, and "since no safe blood lead level in children has been identified, a blood lead 'level of concern' cannot be used to define individuals in need of intervention".[5] The new policy is to aim to reduce average blood lead levels in US children to as low a level as possible.

The CDC now publishes a "reference" blood lead level which they hope they can ratchet downward in coming years. The reference value is "based on the 97.5 percentile of the BLL distribution among children 1 –5 years old in the United States".[6] It is currently 5 μg/dL. According to the CDC, in 2012, "approximately 450,000 children in the United States have BLLs higher than this reference value".[7] (Since there were more than 24 million US children under the age of 6 in 2014, if 2.5% are assumed to have blood lead levels higher than the reference by definition, there were approximately 600,000 US children with elevated blood lead levels in 2014).[8] It is not a level deemed by the CDC as "safe". No level of lead in the blood of children is currently thought to be safe. The reference level is designed to be used as a policy tool. Parents, clinicians, communities, state and federal authorities and political leaders are expected to monitor blood lead test levels, aware that children testing higher than the reference level are testing higher than 97.5% of all US children. The CDC expects action to be taken when test levels are found to exceed the reference. As blood lead levels slowly decline in response to such action, the reference will also decline. CDC will recalculate a new reference every four years.

Preindustrial human BLL is estimated to have been 0.016 ug/dL, and has increased markedly in the aftermath of the industrial revolution. Today, BLL measurements from remote human populations have ranged from 0.8-3.2 ug/dL. Children in populations adjacent to industrial centers in developing countries often have average BLL measurements above 25 ug/dL. In developed countries, governments have sought to regulate lead use in paint, gasoline and other products, and successfully reduced average lead levels among children to below 10 ug/dL for most populations. Blood lead levels remain higher for children, for the poor, for minority or disenfranchised populations, and for people living in cities. The National Academies evaluated this issue[9] in 1991 and confirmed that the blood lead level of the average person in the US was 300 - 500 times higher than that of preindustrial humans.

Lead is toxic and can cause neurological damage, especially among children, at any detectable level. High lead levels cause decreased vitamin D and haemoglobin synthesis, anemia, acute central nervous system disorders, and possibly death.[10]

Historical trends

Prior to the industrial revolution human BLL is estimated to have been far less than it is today. Bone lead measurements from two Native American populations living on the Pacific coast and the Colorado river between 1000-1300 A.D. show that BLLs would have been approximately 0.016 ug/dL.[11][12] The World Health Organization and others interpret these measurements to be broadly representative of human preindustrial BLL.[10]

Contemporary human BLLs in remote locations are estimated to be 0.8 and 3.2 ug/dL in the southern and northern hemispheres, respectively.[10][11] Blood lead levels 50-1000 times higher than preindustrial levels are commonly measured in contemporary human populations around the world.[10]

The creator of the original graphic this one is adapted from was Clair Patterson. He originally developed techniques to measure tiny concentrations of lead in his quest to determine the age of the Earth. When he discovered that preindustrial humans had far less lead in their bodies than all modern humans, he wrote: "It seems probable that persons polluted with amounts of lead that are at least 400 times higher than natural levels, and are nearly one-third to one-half that required to induce dysfunction, that their lives are being adversely affected by loss of mental acuity and irrationality. This would apply to most people in the United States".[13] The original graphic can be seen in the Caltech Archives.

Demographic and geographic patterns

Blood lead levels are highest in countries where lead is added to petrol of gasoline, where lead is used in paint soldered products, in urban areas, in areas adjacent to high road traffic, and in developing countries.[10] In Jamaica, 44% of children living near lead production facilities had BLLs above 25 ug/dL. In Albania, 98% of preschool children and 82% of schoolchildren had BLLs above 10 ug/dL; preschoolers living near a battery factory had average BLLs of 43 ug/dL. In China, 50% of children living in rural areas had BLLs above 10 ug/dL, and children living near sites of industry and high traffic had average BLLs ranging from 22 to 68 ug/dL.[10]

BLL measurements from developed countries decreased markedly beginning in the late 1970s, when restrictions were placed upon lead use in gasoline, petrol, paint, soldering material and other products. In the United States, average BLLs measured among tens of thousands of subjects declined from 12.8 to 2.8 ug/dL between 1976 and 1991.[10] In the 1990s, BLLs of children in Australia were measured to be 5 ug/dL, and 9 ug/dL in Barcelona, Spain.[10]

In the United States, blood lead levels remain highest for children, for people in urban centers, for people of lower socioeconomic status, and for minorities.[14]

Sources

Exposure to lead occurs through ingestion, inhalation, and dermal contact. When exposed to lead, lead enters one’s bloodstream and elevates their blood lead level that results to lead poisoning or an elevated blood lead level.[15] A major source of exposure to lead comes from inhalation. Factories and industries, vehicles exhausts, and even dust in the air that people breathe all have the potential of containing lead. Other major sources of lead exposure also include ingestion and contact with products such as paint and soil that may contain lead as well. Many older claw foot bathtubs have also been found to leach lead, especially when filled with warm bath water.[16]

Health effects

See also: Lead poisoning

The Centers for Disease Control and Prevention (CDC) states "No safe blood lead level in children has been identified. Even low levels of lead in blood have been shown to affect IQ, ability to pay attention, and academic achievement. Effects of lead exposure cannot be corrected".[17] "The absence of an identified BLL without deleterious effects, combined with the evidence that these effects appear to be irreversible, underscores the critical importance of primary prevention"[18]

The most sensitive populations are infants, children, and pregnant women.

A kid can drink a glass of water containing lead and absorb 50% of it. An adult might only retain 10% of what’s in that glass. And once the lead is in the kid’s body, it gets to the kid’s brain through the not fully developed blood brain barrier. The body removes lead from blood and stores it in bone, but in kids it also comes back out of bone readily compared to adults.[19][20] "Lead that has accumulated in a woman’s bones is removed from her bones and passes freely from mother to child; maternal and fetal blood lead levels are virtually identical. Once in the fetal circulation, lead readily enters the developing brain through the immature blood–brain barrier".[21]

"Lead is associated with a wide range of toxicity in children across a very broad band of exposures, down to the lowest blood lead concentrations yet studied, both in animals and people. These toxic effects extend from acute, clinically obvious, symptomatic poisoning at high levels of exposure down to subclinical (but still very damaging) effects at lower levels. Lead poisoning can affect virtually every organ system in the body. The principal organs affected are the central and peripheral nervous system and the cardiovascular, gastrointestinal, renal, endocrine, immune and haematological systems".[22]

Adults who are exposed to a dangerous amount of lead can experience anemia, nervous system dysfunction, weakness, hypertension, kidney problems, decreased fertility and increased level of miscarriages, and low birth weight and premature deliveries[23]

See also

Notes

  1. ↑ http://web.archive.org/web/20110331121705/http://www.health.nsw.gov.au/publichealth/chorep/env/env_pbhem.asp. Archived from the original on March 31, 2011. Retrieved June 20, 2011. Missing or empty |title= (help) Government of New South Wales, Australia: Blood lead levels in Broken Hill children
  2. ↑ "Update on Blood Lead Levels in Children". Centers for Disease Control and Prevention. Retrieved 4 February 2016.
  3. ↑ "CDC Response to Advisory Committee on Childhood Lead Poisoning Preventio" (PDF). Retrieved 5 February 2016.
  4. ↑ "CDC Response to Advisory Committee on Childhood Lead Poisoning Preventio" (PDF). Retrieved 5 February 2016.
  5. ↑ "CDC Response to Advisory Committee on Childhood Lead Poisoning Preventio" (PDF). Retrieved 5 February 2016.
  6. ↑ "CDC Response to Advisory Committee on Childhood Lead Poisoning Preventio" (PDF). Retrieved 5 February 2016.
  7. ↑ "CDC Response to Advisory Committee on Childhood Lead Poisoning Preventio" (PDF). Retrieved 5 February 2016.
  8. ↑ "Number of Children Tested and Confirmed BLL's ≥10 µg/dL by State, Year, and BLL Group, Children < 72 Months Old". Retrieved 5 February 2016.
  9. ↑ "Measuring Lead Exposure in Infants, Children, and Other Sensitive Populations (1993)". National Academies Press. Retrieved Feb 3, 2016.
  10. 1 2 3 4 5 6 7 8 Tong, Shilu; von Schimding, Yasmine; Prapamontol, Tippawan (2000). "Environmental lead exposure: a public health problem of global dimensions". Bulletin of the World Health Organization 78.
  11. 1 2 Patterson, Clair; Ericson, Jonathan; Mirela, Manea-Krichten; Shirahata, Hiroshi (1991). "Natural skeletal levels of lead in Homo sapiens sapiens uncontaminated by technological lead". The Science of the Total Environment 107: 205–236.
  12. ↑ Flegal, A. Russell; Smith, Donald (1992). "Lead Levels in Preindustrial Humans". The New England Journal of Medicine 326 (19): 1293–4.
  13. ↑ Denworth, Lydia. Toxic Truth. Beacon Press. p. 111. ISBN 978-0-8070-0032-8.
  14. ↑ Jones, Robert; Homa, David; Meyer, Pamela; Brody, Debra; Caldwell, Kathleen; Pirkle, James; Brown, Mary Jean (2009). "Trends in Blood Lead Levels and Blood Lead Testing Among US Children Aged 1 to 5 Years, 1988–2004". Pediatrics 123 (3): e376.
  15. ↑ Stellman, Jeanne Mager (1998). Encyclopaedia of Occupational Health and Safety. International Labour Organization. pp. 81.2–81.4.
  16. ↑ Agency for Toxic Substances and Disease Registry (August 2007). "ATSDR Toxicological Profile for Lead" (PDF). Retrieved 2012-03-15.
  17. ↑ "What Do Parents Need to Know to Protect Their Children?". Retrieved 2016-02-04.
  18. ↑ "CDC Response to Advisory Committee on Childhood Lead Poisoning Recommendations" (PDF). Retrieved 2016-02-04.
  19. ↑ "Childhood Lead Poisoning" (PDF). World Health Organization. Retrieved 5 February 2016.
  20. ↑ "Almost all adults in the US had more lead in their blood when they were kids than the worst hit children in Flint". Retrieved 5 February 2016.
  21. ↑ "Childhood Lead Poisoning" (PDF). World Health Organization. Retrieved 5 February 2016.
  22. ↑ "Childhood Lead Poisoning" (PDF). World Health Organization. Retrieved 5 February 2016.
  23. ↑ "Lead Toxicity What Are the Physiologic Effects of Lead Exposure?". Retrieved 5 February 2016.

References

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