Medical insights brought by lead x-ray fluorescence technology: lead exposure, cognitive
decline, and Parkinson’s Disease
Medphys 4T03
January 30, 2020
In-viva x-ray fluorescence (XRF) technology for measuring bone lead concentration has grown as
an important tool for epidemiological studies of lead toxicity.1 While using a low activity source, gamma
rays are emitted onto a lead atom in order to remove an inner-shell electron, causing the atom to enter
into an excited state.1 De-excitation then results in the emission of an x-ray, with lead-specific energy,
and the detection of this x-ray by a radiation detector.1 The number of x-rays detected can then be used
to determine the amount of lead present in the bone in question.1
Lead is one of the oldest occupational toxins with historical poisoning dating back to Roman times.2 Lead
poisoning occurrences have taken place in both occupational and non occupational settings with the
general public being affected for years from various sources, including: ceramic ware, food canning,
drinking water, paint, and much more.2 With the growing attention to lead exposure and the potential
health risks, several studies have been conducted and have revealed associations between lead
exposure and a range of health impacts, including, increased blood pressure, early menopause,
antisocial and delinquent behaviour in children, intellectual deficits in children, cardiovascular disease,
and more.3,4
Lead toxicity has been known to target the central nervous system.5 Low lead doses have been linked
with symptoms such as irritability, sleep disturbances, poor attention and concentration, forgetfulness
and depressed affect.5 Less noticeable deficits related to lead exposure have become a topic of growing
attention and research over the last three decades.5 Two neurological health impacts, in particular, have
undergone much research in relation to lead exposure: cognitive decline and increased risk of
Parkinson’s Disease (PD).
This report serves as a review of recent studies that have been done to further explore these two
specific health impacts. Below is a review of six studies which explore the potential link between lead
exposure and cognitive decline and two studies which explore the link between lead exposure and the
risk of developing PD.
Schwartz, B. S. et al, 2005.
The study was conducted from 1997 to 2001 on 803 lead workers in South Korea.5 The purpose
was to examine the effects of long-term occupational lead exposure on the central and peripheral
nervous system.5 This was done by measuring lead concentration in the tibia using XRF. Tibia lead was
measured using 109Cd K-shell XRF and was performed on the left mid-tibia for a 30 minute
measurement.6 The results showed that tibia lead concentrations are associated with an annual decline
in test scores, specifically regarding executive abilities, manual dexterity, and peripheral vibration
threshold.5 The study supports the idea that occupational lead exposure may be associated with
cognitive function decline over time and that cumulative dose, in particular, influences the longer-term
effect on cognitive decline, rather than recent dose.5
Weisskopf, M. G. et al, 2007.
The study was conducted from 1991 to 1999 on 1089 community-dwelling elderly men.7 The
purpose was to examine the effects of nonoccupational lead exposure on cognitive functions.7 This was
done by measuring bone lead concentration by K-shell XRF at two locations, the mid tibia and the
patella, for 30 minute measurements.7 Comparing the lead measurements to cognitive tests showed
that all test scores declined as bone lead concentration increased.7 Interestingly, the strongest effects
were seen on the scores for visuospatial/visuomotor testing.7 The study supports the idea that low-level
lead exposure in a cumulative and nonoccupational fashion may negatively impact cognitive function,
especially visuospatial/visuomotor functions.7
Power, M. C. et al, 2014.
The study was conducted from 1993 to 2008 on 584 women, aged 45-74, who belonged to a
nurse’s health study from Boston, Massachusetts.8 The purpose was to examine whether lead exposure
was associated with cognitive decline in women.8 This was done by measuring bone lead concentrations
by K-shell XRF at two sites, the mid tibia and the patella, with tibia lead concentration reflecting a longer
time period compared to patella lead concentration.8 The results showed increased lead concentration
in the tibia came with greater cognitive decline, particularly with test scores related to story memory
and category influence.8 There was little association between cognitive decline and patella lead
concentrations.8 The study supports the idea that cumulative lead exposure in women over a long time
period may be weakly associated with faster cognitive decline in women.8
Shih, R. A. et al, 2006.
The study was conducted on 991 adults, aged 50 to 70, from Baltimore and coming from an
array of demographics.9 The purpose was to examine the potential association between cognitive
decline in adults and environmental lead levels. This was done by measuring bone lead concentrations
using 109Cd K-shell XRF 30 minute measurements of the mid tibia.9 The results indicate that higher lead
concentrations in the tibia are associated with worse cognitive functions in all measured areas,
including: language, processing speed, eye-hand coordination, executive functioning, verbal memory
and learning, visual memory, and visuoconstruction.9 The study supports the idea that cumulative lead
dose, retained from previous environmental exposure, may have persistent negative effects on cognitive
function and, furthermore, earlier lead exposure may be associated with certain age-related cognitive
declines.9
Stewart, W. F. et al, 2006.
The study was conducted on 532 former lead workers with an average age of 56 and who have
been removed from occupation lead exposure for an average of 18 years.10 The purpose was to see if
cumulative occupational lead dose is associated with white matter lesions (WML) and global and
structure-specific brain volumes.10 Both white matter lesions and brain volume have been associated
with cognitive decline.11,12 Tibia lead concentrations was measured using 109Cd K-shell XRF with 30
minute measurements of the mid tibia.10 The results showed that higher tibia lead concentration was
associated with increasing WML grade and that higher tibia lead related to smaller total brain volume,
frontal and total gray matter volume, and parietal white matter volume.10 Furthermore, smaller brain
regions with smaller volume associated to higher tibia lead included the cingulate gyrus and the insula.10
The study supports the idea that cumulative occupational lead dose is associated with brain lesions and
declining brain volume.
Weuve Jennifer et al, 2009.
The study was conducted on 587 community dwelling women, aged 47-74 years.13 The purpose
was to examine whether chronic low-level lead exposure is associated with accelerated cognitive decline
in older age, specifically in women.13 This was done by measuring bone lead concentrations in the mid
tibia and patella using K-shell XRF. 13 All of the cognitive tests showed worse cognitive performance
associations with the lead biomarkers, however only the tibia results were statistically significant.13
Furthermore, the association between bone lead and letter fluency was very different from the other
cognitive score – bone lead associations. The study supports the idea that lead exposure may have
negative effects on women’s aging cognition, even at low leads levels experienced within community
settings.
Weisskopf, M. G. et al, 2010.
The study was conducted on 330 patients with Parkinson Disease (PD).14 The purpose was to
explore whether heavy metal exposures, including lead, was associated with an increased risk in PD.14
This was done by measuring bone lead concentrations using 109Cd K-shell XRF 30 minute measurements
of the mid tibia.14 Odd ratios (ORs) for PD were compared between the 4 quartiles of tibia bone lead in
the cohort.14 The results show an increasing chance of PD with increasing tibia lead concentration and
the OR for PD in the highest quartile compared to the lowest quartile was 3.21 with a 95% confidence
interval.14 No association was found with patella bone lead, which is related to a shorter-term
exposure.14 The study supports the idea that cumulative exposure to lead increases the risk of PD.
Coon Steven et al, 2006.
The study was conducted on 121 Parkinson disease patients.15 The purpose was to examine
whether there is an association between PD and heavy metal exposure measurements, specifically lead
exposure.15 This was done by measuring lead bone concentrations in the tibia and calcaneal bone using
109
Cd K-shell XRF.15 The results illustrate that the risk of PD is elevated more than two fold for individuals
in the highest quartile of lifetime exposure to lead compared to the lowest quartile.15 This study
supports the idea that cumulative lead exposure in an occupational setting is a risk factor for PD.
Conclusion
These studies highlight several important insights into medical knowledge brought about by the use
of lead x-ray fluorescence technology. Specifically, it is clear that multiple studies have found consistent
association between cumulative, long term lead exposure with both cognitive decline and PD.
Cumulative and persistent, rather than short-term, lead exposure is linked to declines in several
cognitive functions, including: executive abilities, manual dexterity, peripheral vibration threshold and
visuospatial/visuomotor functions.5,7 When studying the effects on women in particular, cognitive
decline seems to occur at a faster rate as a result of cumulative lead exposure, in both occupational and
nonoccupational settings.8,13 Even after years of being removed from the exposure, it has been shown
that long-term cognitive effects are being experienced and earlier first exposure may be linked to
different cognitive declines.9 In order to understand these cognitive decline trends within an anatomical
context, it has been shown that cumulative lead exposure is linked to brain lesions and declining brain
volume.10 Lastly, when comparing PD patients with matched controls, it has been found that cumulative
lead exposure has a significant increase in the risk of developing PD.
References
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