Lead mining in Southern Scotland. The beam engine at the former lead mine in Wanlockhead, c. 1900. This now forms part of the Lead Mining Museum. Photograph by courtesy of the Wanlockhead Museum Trust.
Inorganic lead compounds have been known to be a toxic hazard for many hundreds of years. Control of lead exposure at work is covered by regulations (Control of Lead at Work, or CLAW)1 which stipulate regular blood lead monitoring. Environmental exposure to lead has reduced considerably with the introduction of lead-free petrol, removal of lead from paint, reduction of lead in potable water supplies, removal of lead plumbing, and treatment of water to reduce plumbosolvency. Nevertheless, lead poisoning can still occur, usually as a result of occupational exposure, in plumbers, stain glass window workers, paint strippers etc.
Blood lead measurement provides a reliable guide to lead exposure; the industrial action limit, above which workers are legally required to be suspended from work, is currently 2.90 µmol/L (60 µg/100 mL). Lead inhibits several enzymes in the haem cycle and so concentrations of several porphyrins increase especially when blood lead exceeds 2.0 µmol/L. At about this concentration other effects may result such as fatigue, depression, irritability, cognitive impairment, headaches, weakness and constipation. More severe poisoning may cause anaemia, renal tubular dysfunction and peripheral neuropathy. Zinc protoporphyrin (ZPP) can be measured as an alternative marker although this analyte also falls in patients with iron deficiency anaemia.
In children lead may have neurological effects. Children are more prone to exposure since intestinal absorption is more efficient than in adults. Pica, the repetitive ingestion of non-food substances by young children, may present a hazard in poorly maintained housing with lead-based paint. Lead poisoning may occur in various ethnic populations following ingestion of traditional remedies or application of eye cosmetics. This is now the commonest form of lead poisoning in children.
Subtle toxic effects of lead on behaviour can be found even in children whose blood lead concentrations are normal. In 2012 the US Center for Disease Control (CDC) reduced the reference range of lead in children under five years to 0.24 µmol/L2.
The measurement of urinary lead is only recommended for monitoring of chelation therapy or for assessment of exposure to alkyl-leads.
Results from the most recent population survey of blood lead concentrations in the United States showed that the 97.5th percentile is at 5 µg/dL (0.024 µmol/L) and this is now the CDC upper reference value, replacing the previous 10 µg/dL ‘level of concern’.
The traditional remedies of a number of ethnic groups may contain substantial amounts of lead and several instances of clinical lead poisoning by ingestion of Asian traditional remedies have been reported in the U.K. Middle Eastern and Asian eye cosmetics may also contain lead, and their use on infants or by their mothers is associated with increased blood lead levels in the infants concerned.
1. CLAW Regulations: http://www.hse.gov.uk/pubns/priced/l132.pdf
2. CDC. CDC response to Advisory Committee on Childhood Lead Poisoning Prevention recommendations in “Low level lead exposure harms children: a renewed call for primary prevention.” Atlanta, GA: US Department of Health and Human Services, CDC; 2012. Available at http://www.cdc.gov/nceh/lead/acclpp/cdc_response_lead_exposure_recs. pdf. 3. Chandramouli K, Steer CD, Ellis M, Emond AM. Effects of early childhood lead exposure on academic performance and behaviour of school age children. Arch Dis Child 2009. 94: 844-848.
4. GLASS (Global Lead Advice and Support Service). http://www.lead.org.au/fs/fst67.html
5. Menke A, Muntner P, V, Silbergeld EK, Guallar E. Blood lead below 0.48 μmol/L (10 μg/dL) and mortality among US adults. Circulation. 2006; 114: 1388-1394
Sample Requirements and Reference Ranges for Lead
|Sample Type||Blood, urine, water|
Blood: EDTA or lithium heparin1
Urine / water: Universal container
|Precautions||Blood samples for occupational exposure should be taken at the end of a working shift.|
Blood: 300 µL
Blood Lead: < 0.24 µmol/L (5 µg/100mL)
> 2.0 µmol/L (40 µg/100mL) (can cause clinical effects)3
> 2.90 µmol/L (60 µg/100mL) (occupational exposure limit)
ZPP: < 30 to 80 nmol/mol haem
Urine lead: < 110 µg/g creatinine (occupational exposure limit)
Water: < 10 µg/L Current EEC limit for drinking water
1 week (please telephone 0141 211 4494 if immediate turnaround required)
|Method||Graphite furnace / atomic absorption spectrometry|
UK NEQAS, Guildford; Wadsworth, New York;
UK NEQAS Cd and Pb, Birmingham.
- One sample of blood is sufficient for blood lead and porphyrin analysis.
- For assessment of lead in water, two samples are required; a first draw sample in the morning and a further sample taken after running the water for 5 - 10 mins.
- Significant exposure in adults is present when values reach 2.0 µmol/L, and in children 1.35 µmol/L.
* This is the absolute minimum volume; these volumes are insufficient to carry out a repeat analysis in the event of an analytical problem.