Environmental Laboratory 17


Major Source of Lead Currently the major source of lead poisoning among children comes from lead-based household paints, which were used up until they were banned in 1978 by the Consumer Product Safety Commission. Prior to this, leaded gasoline was the largest pollutant before it was completely removed from the pumps in 1995. Other potential sources include lead pipes used in drinking water systems, airborne lead from smelters, clay pots, pottery glazes, lead batteries, household dust and some processed foods made from natural plants and crops. However, awareness of the problem combined with preventative care and regular monitoring, have reduced the percentage of children aged 1–5 years with elevated blood levels (≥3.5 μg/dL) in the US from 26% in the early-mid 1990s to less than 2.5% today. These data were taken from a recent National Health and Nutrition Examination Survey (NHANES) report (8).


Routine Monitoring of Lead Using


Atomic Spectroscopic Techniques There is no question that the routine monitoring of lead has had a huge impact in reducing the number of children with elevated blood levels. Lead assays were initially carried out using the dithizone colorimetric method, which was sensitive enough, but very slow and labour intensive. It became a little more automated when anodic stripping voltammetry was developed (9), but blood-lead analysis was not considered a truly routine method until AS techniques became available. Let’s take a more detailed look at how improvements in atomic spectroscopy instrumentation detection capability have helped to lower the number of children with elevated blood lead levels, since atomic absorption was fi rst commercialised in the early 1960s.


Flame AA When FAA was fi rst developed, the BLRV was 60 µg/dL (600 ppb). Even though this is well above the detection limit of ~20 ppb at the time, it struggled to meet this level when sample preparation and dilution of the blood samples was taken into consideration, which typically involved acid digestion followed by dilution and centrifuging/fi ltering. When sample preparation was factored, the concentration of lead in the sample was in the order of 20 ppb – virtually the same as the FAA detection limit.


Delves Cup AA To get around this limitation, an accessory called the Delves Cup was developed in the late 1960s to improve the detection limit of FAA (10). The Delves Cup approach uses a metal crucible, which was positioned over the fl ame. The sample is pipetted into the crucible, where the heated sample vapour is passed into a quartz tube, which was also heated by the fl ame. The ground state atoms are concentrated in the tube and therefore resident in the optical path for a longer period of time, resulting in much higher sensitivity and about 100x lower detection limits. The Delves Cup became the standard method for carrying out blood lead determinations for many years, because of its relative simplicity and low cost of operation.


Electrothermal Atomization The Delves Cup approach eventually got phased out with the commercialization of electrothermal atomization (ETA) or graphite furnace AA in the early-1970s. This new breakthrough technique offered a detection capability for lead of ~ 0.1 ppb – approximately 200x better than FAA. However, its major benefi t for the analysis of blood samples was the ability to dilute and inject the sample automatically into the graphite tube with very little off-line sample preparation. This result was that blood lead determinations could now be carried out in an automated fashion with relative ease, even at very low levels.


Zeeman Correction GFAA The next major milestone in AA was the development of Zeeman background correction (ZBGC) in 1981, which compensated for


Figure 2: Comparison of detection capability of AS techniques (ppb) for lead and the approximate year they were developed, or improvements were made


non-specifi c absorption and structured background produced by complex biological matrices, like blood and urine (11). This, in conjunction with the STPF (stabilised temperature platform furnace) concept, allowed for virtually interference-free analysis of blood samples, using aqueous calibrations and as a result became the recognised way of analysing most types of complex matrices by ETA (12).


ICP-MS Even though ETA had been the accepted way of doing blood lead determinations for over 15 years, the commercialisation of quadrupole-based ICP-MS in 1983 gave analysts a tool that was not only 100x more sensitive but suffered from less severe matrix-induced interferences. In addition, ICP-MS offered multielement capability and much higher sample throughput. These features made ICP-MS very attractive to the clinical community, such that many labs converted to ICP-MS as their main technique for trace element analysis. Then as the technique matured, utilising advanced mass separation devices, performance enhancing tools, powerful interference reduction techniques and more fl exible sampling accessories, detection limits in real-word samples improved dramatically for some elements. Figure 2 shows the improvement in lead detection capability (in ppb) of ICP-MS compared the other AS techniques.


It should also be emphasised these are instrument detection limits (IDLs), which are based on simplistic calculations of aqueous blanks carried out by manufacturers and not realistic method detection limit (MDL) into consideration the sample preparation procedure, dilution steps and multiple analytical measurements (13). For that reason, a 10-50 x degradation in IDL is quite common for a real-world method limit of quantitation (LOQ).


Final Thoughts There is no question that developments in atomic spectroscopy have helped us better understand the toxicity effects of lead over the past 50 years. As Figure 3 clearly demonstrates, there is a direct correlation between the lowering of the CDC blood-lead levels and the detection capability of ICP-MS. It has allowed us to lower the clinical practice threshold level of 60 µL/ dL in the mid-1960s to the current blood lead reference value (BLRV) of 3.5 µL/dL. More importantly, it has helped to reduce elevated blood levels of children in the U. S., from 26 % in the early-mid-1990s to less than 2.5% today, as well as allowing us to get a much better understanding of the environmental sources of lead contamination. However, such is the power and versatility of modern atomic spectroscopy instrumentation and its accessories, that it has also dramatically improved our understanding of other trace metal-related human diseases. The toxic effects of trivalent/pentavalent arsenic and hexavalent chromium would still be relatively unknown, if it wasn’t for the continual improvements in ICP-MS and in particular, its use as a very sensitive detector for trace element speciation studies using chromatographic separation technology. Even though ICP-MS has been successfully applied to many application areas since it was fi rst commercialised in 1983, its use as a biomedical, clinical and toxicological research tool has had a direct impact on the quality of many people’s lives.


Further Reading 1. Practical Guide to ICP-MS and Other Atomic Spectroscopy Techniques A Tutorial for Beginners, 4th Edition, R.J. Thomas, CRC Press, Boca Raton, FL, ISBN – 978-1-032-03502-4


2. Preventing Lead Poisoning in Young Children, Chapter 2: Absorption of Lead, Centers for Disease Control and Prevention (CDC), 1991, https://www.cdc.gov/nceh/lead/publications/ books/plpyc/contents.htm


3. H. L. Needham, Case Studies in Environmental Medicine-Lead Toxicity, U. S. Dpt. of Health and Human Services (1990)


4. Preventing Lead Poisoning in Young Children, Lead Information Page, Centers for Disease Control and Prevention (CDC), https://www.cdc.gov/nceh/lead/default.htm


5. Childhood Blood Lead Levels in Children Aged <5 Years: United States, 2009–2014, Morbidity and Mortality Weekly Report (MMWR), Surveillance Summaries / January 20, 2017 / 66 (3);1– 10, https://www.cdc.gov/mmwr/volumes/66/ss/ss6603a1.htm


6. CDC Response to Advisory Committee on Childhood Lead Poisoning Prevention Recommendations in “Low Level Lead Exposure Harms Children: A Renewed Call of Primary Prevention” (2012) , https://www.cdc.gov/nceh/lead/ACCLPP/ blood_lead_levels.htm


7. Record of Proceedings from the Meeting of the Lead Poisoning Prevention Subcommittee of the NCEH/ATSDR Board of Scientifi c Counselors, Centers for Disease Control and Prevention (CDC), Atlanta, GA, September 19, 2016


8. Centers for Disease Control and Prevention (CDC), Morbidity and Mortality Weekly Report (MMWR), October 7, 2016 / 65(39); 1089, Source: The National Health and Nutrition Examination Survey (NHANES); http://www.cdc.gov/nchs/nhanes/index.htm.


9. S. Constantini, R. Giordano, M. Rubbing. Journal of Microchemistry, 35,70 (1987)


10. H. T. Delves, Analyst, 95, 431 (1970)


Figure 3: The improvement in real-world detection capability (in µg/dL) offered by AS techniques for blood-lead determinations compared to the trend in blood-lead levels set by the CDC


Figure 3 is a combination of fi gures 1 and 2 and shows the improvement in detection capability (in µg/dL) offered by AS techniques for blood-lead determinations compared to the trend in blood-lead levels set by the CDC. Both plots are shown in log scale, so they can be viewed on the same graph.


11. S. Cabet, J. M. Ottoway and G. S. Fell, Research and Development Topics in Analytical Chemistry, Proc. Analyt. Div. Chem. Soc., 300 (1977)


12. W. Slavin, Sci. Total Environ., 71, 17 (1988)


13. Quality Assurance of Chemical Measurements, 1st Edition, J. K. Taylor; CRC Press, Boca Raton, FL, ISBN 9780873710978, (1987)


Robert Thomas, Scientifi c Solutions • 4615 Sundown Rd, Gaithersburg, MD 20882, USA • Tel (Cell): (1) 301-717-0900 • Email: robert.james.thomas@verizon.net • Web: www.scientifi csolutions1.com


Robert (Rob) Thomas is the principal scientist at Scientifi c Solutions, a consulting company that serves the educational needs of the trace element user community. He has worked in the fi eld of atomic and mass spectroscopy for almost 50 years, including 24 years for a manufacturer of atomic spectroscopic instrumentation. Rob has written overt 100 technical publications, including a 15-part tutorial series entitled, A Beginner’s Guide to ICP-MS. He is also the editor and frequent contributor of the Atomic Perspectives column in Spectroscopy magazine, as well as serving on the editorial advisory board of Analytical Cannabis. In addition, Rob has authored 6 textbooks on the fundamental principles and applications of ICP-MS. His most recent book is entitled, A Practical Guide to ICP-MS and Other AS Techniques, which was published in September, 2023. Rob has an advanced degree in analytical chemistry from the University of Wales, UK, and is also a Fellow of the Royal Society of Chemistry (FRSC) and a Chartered Chemist (CChem).


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