Screening
& Diagnosis
DETERMINATION
OF BLOOD LEAD LEVELS USING
PROTON
INDUCED X-RAY EMISSION(PIXE) TECHNIQUE
Dr.
R.K.Choudhury
Abstract
Quantitative analysis
of lead levels in blood is important from the point of monitoring the
effect of environment pollution on the human health. Particle induced
x-ray emission studies provide a unique method to carry out simultaneous
multi-element analysis of samples with very good accuracy and sensitivity.
This method was used by us to determine the blood lead levels in children
admitted to hospital in Mumbai with suspected lead poisoning, ascribable
to environmental pollution from heavy vehicular traffic and industrial
sources. The lead concentration in the blood samples of the patients
varied from 10 to 600m gm/dl. This paper describes the present
work and other related recent studies on environmental pollution of
lead.
Introduction
Increased use of
automobiles in cities in developing countries is causing lead poisoning
due to the presence of tetralkyl lead in gasoline products. Studies
of lead levels in the atmosphere and in human tissues including blood
have been carried out by many authors [ 1-5] . It was shown
by Nriagu [ 6] after a global assessment of the atmospheric
trace metals that lead as an environmental pollutant is essentially
of anthropogenice origin caused by human intervention.
Lead poisoning is
known to cause a series of health disorders. Recent epidemiological
studies [ 7-9] show that the mental and behaviourial developments
in children are adversely affected by exposure to very low levels of
lead. Lead pollution must, therefore, be regarded as a threat to children’s
health in every country. Blood lead levels exceeding 10m gm/dl
in humans are considered to be of potential risk. Effective monitoring
and control of environmental pollution level is necessary to keep the
lead levels of the exposed population to within acceptable limits. Most
of the work reported on Pb level analysis make use of the atomic absorption
spectroscopy with the commercially available spectrometers. We had carried
out[ 10] the studies of blood levels in children residing in
high traffic density area of Mumbai and admitted to Sion hospital in
Mumbai with suspected lead poisoning, using the proton induced x-ray
emission (PIXE) technique. In addition to lead, other elements such
as K, Ca, Fe, Cu, Zn, Se, Br and Rb were also detected simultaneously.
We give below a brief description of the PIXE set up and discuss the
results obtained in that study.
Proton Induced
X-ray Emission (pixe) Method
The PIXE set up
used at the Van-de Graaff accelerator at Trombay is shown in fig.1.
Proton beam of 2.5 MeV was bombarded on the samples to produce the characteristic
x-rays of the elements present in the sample. The beam from the accelerator
is first passed through a Ni diffuser foil and then through a set of
collimators before striking the sample over a well defined area. The
x-rays from the sample are detected at right angles to the beam direction
with a liquid nitrogen colled Si(Li) detector. The detector was shielded
from all sides except the Be window which interfaces the sample and
the detector.
Fig. 2 Proton induced
X-ray emission spectrum of blood from a patient suspected of lead poisoning.
Results and Discussion
The samples (total
36 nos.) were collected from children of both sexes aged 1-12 years
and were grouped on the basis of clinical findings such as hypochromic
microcytic anaemia, gastrointestinal symptomology, encephalopathy of
unknown actiology, mental retardation and pica. Control samples (20
nos.) were also analysed for comparison with the data from the patient
groups. All five clinical groups exhibited a high incidence of Pb levels,
with an average value of 151 m gm/dl. The frequency distribution
of lead concentration in all the samples is shown in fig. 3. The average
value of Pb concentration from the control group was 30m gm/dl,
which itself is large compared to the acceptable limit of 10m gm/dl
for the normal population. The samples having significantly elevated
(> 140 m gm/dl) blood lead levels belonged mostly to the patients
of encephalopathy, pica and anaemia groups. As seen from the figure,
even the control group of children coming from the high density traffic
area showed high blood Pb levels. Although these controls were apparently
from healthy children, air pollution could be the main cause for the
high blood lead levels. The concentrations of other elements such as
Fe, Cu, Zn, Se, Rb were also determined by the PIXE analysis. With the
limited sample sets analyzed in this study, there was no apparent correlation
seen between the concentrations of Pb and other elements. The average
Fe concentration for the anaemia group was seen to be 175 ± 22m
gm/dl, which is significantly lower than the average value of 341 ±
147m gm/dl for all patient samples and the average value of 546
± 97 m gm/dl for the control samples. Similarly the average
Rb concentration for all the patient samples was seen to be 1.85 ±
1.09 m gm/dl, which is somewhat lower in comparison to the control
average of 2.8 ± 0.68 m gm/dl. The average concentrations
of other elements in the patient samples did not
show any significant
deviation from the control samples.
Conclusions
The PIXE technique
is seen to be a powerful tool for simultaneous analysis of blood Pb
levels and other elements present in samples and can be exploited for
various medical applications. PIXE set ups are currently available also
at the Institute of Physics, Bhuwaneswar and the National Centre for
Compositional Characterisation of Materials, Hyderabad. The potentials
of the PIXE technique can be exploited for large varieties of medical
applications, using the facilities available within the country.
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