Download Radiological implications of lead: A review article

Sky Journal of Medicine and Medical Sciences Vol. 4(7), pp. 056 - 059, September, 2016
Available online http://www.skyjournals.org/SJMMS
ISSN 2315-8808 ©2016 Sky Journals
Review
Radiological implications of lead: A review article
Nkubli B. F.1, Nzotta C. C.2, Luntsi G1*, Nwobi I. C1.
1
Department of Medical Radiography, College of Medical Sciences, University of Maiduguri, Borno State, Nigeria.
Department of Radiography and Radiological Sciences, Faculty of Health Science and Technology, College of Health
Sciences, Nnewi Campus, Nnamdi Azikiwe University, Awka Anambra State, Nigeria.
2
Accepted 20 June, 2016
Lead and lead-based materials have varied applications in diagnostic radiology. These uses are more relevant
in the area of radiation protection but pose a challenge at the point of disposal. This review explores the uses of
lead and lead-based materials in diagnostic radiology and the public and environmental health implications of
the disposal of waste originating from such uses. An extensive literature search was conducted using various
search terms such as lead, lead shielding, radiological implications of lead and uses of lead in radiology and
lead disposal strategies. There was no restriction on dates of article publication due to apparent paucity of
literature on the subject. Lead is a highly toxic metal which should not be disposed of as conventional garbage.
While researchers have explored the uses of lead and its possible health implications in household items,
industries, and mining activities, there exist a gap in knowledge on the use of lead in health care and its
disposal strategies. This review has brought to focus an important but often neglected area of research on lead
use; radiological implications of lead. The applications of lead in diagnostic radiology are numerous especially,
in the area of protecting patients, staff, and the general public from the harmful effects of ionizing radiation.
Out-of-use lead sources from diagnostic radiology could pose a threat to public and environmental health if not
properly disposed of.
Key words: Lead, radiology, public, environmental health.
INTRODUCTION
Lead is an element in the periodic table with the symbol
Pb (Latin plumbum), a dense, bluish-gray metallic
element. The atomic number of lead is 82; the element is
in group 14 of the periodic table (Alkhatib et al., 2014). It
is the heaviest non-radioactive metal that occurs naturally
in the earth crust. Metallic lead is a soft, malleable and a
ductile metal. It has low tensile strength and is a poor
conductor of electricity. A freshly cut surface has a bright
silvery luster, which quickly turns to the dull, bluish-gray
color. Lead melts at 327.46°C (621.43°F), boils at 1749°C
(3180°F), and has a specific gravity of 11.35; the atomic
weight of lead is 207.2.
Pure lead can combine with other substances to form
various lead compounds (Chong-huai et al., 2013). Under
the occupational health and safety (Lead) regulation
2000, lead means pure lead, lead alloys such as solder
*Corresponding author. E-mail: [email protected]. Tel.:
+2348063624220.
or brass, inorganic lead compounds such as lead oxide,
and lead salts of organic acids. The risks involved in
using lead depend on how the lead is being handled. For
example lead in solid ingot form, solders containing lead
and lead-coated substances will present little or no risk to
workers. However, Lead in these forms can present a risk
when it is processed in a way that produces lead dust,
fumes or mist (grinding or heating) (Chong-huai et al.,
2013; Occupational Health and Safety (Lead) Regulation,
2000; Schutz et al., 2005).
High lead exposure is known to be harmful to both
adults and children (Abadin et al., 2007), although, the
typical exposure pathways and effects are somewhat
different. Children are more susceptible to the toxic
effects of lead than adults due to increased exposure
from contaminated soils resulting from hand- to- mouth
transfer behavior (Macloe et al., 2002). The main sources
of lead in children’s environment are diet, lead-based
paint in older housing, lead in soil and dust from
contaminated leaded paint and gasoline, or past and
Nkubli
present mining and industrial activity (Chong-huai et al.,
2013; Mielke, 2002; Chung et al., 2001). Exposure from
the air and waterborne sources have been greatly
reduced with the introduction of unleaded gasoline and
the replacement of lead water pipes and water tanks with
nonleaded alternatives. Lead processes are used in
manufacturing lead-based glazes (Occupational Health
and Safety (Lead) Regulation, 2000; Meyer et al., 2008).
From a diagnostic radiological standpoint, lead is the
most common shield against x-rays because of its high
density, low cost, and ease of installation (Nzotta and
Udeh (2010). Even though there have not been sufficient
data and basis for comparison of the shielding efficiency
of lead and concrete as obtained in various local
environments, a study by Nzotta and Udeh (2010)
showed that lead is a more efficient shield than concrete
within the x-ray diagnostic energy range. A similar study
where the shielding properties of lead aprons and nonlead aprons for both direct x-rays and scattered x-rays in
interventional radiology procedures were compared
observed that for direct x-rays, the protective effects of
lead aprons were superior to that of non-lead aprons at
over 100 kV. Since the k-absorption edge of lead is
higher than that of non-lead material, the shielding effects
of lead increases at higher x-ray energies (>100 kV). In
contrast for scattered x-rays, the shielding effects for lead
and non-lead aprons were similar; consequently, the
protective effects were essentially uniform from 60 to 120
kV (even when over 100 kV). This is because the energy
of scattered x-ray is lower than that of direct x-ray at the
same tube voltage so the k-absorption of lead cannot be
used; hence, for scattered x-rays, the shielding effects of
lead apron is similar to that of a non-lead apron
(Masayuki et al., 2008). This desirable quality of lead
being efficient at providing x-ray shielding at higher x-ray
energy makes lead a suitable material for radiation
protection among other uses in diagnostic radiology.
While the potential risk associated with the use of leadbased materials have been explored across different
works of life and disciplines Alkhatib, 2014; Lim et al.,
2015; Liao et al., 2016). The potential risk associated with
the large quantity of lead and lead-based materials used
within the domains of diagnostic radiology for various
purposes have not been adequately explored in
developing countries (Masayuki et al., 2008; Daniel and
Matthew, 2014). This is evidenced by the paucity of
literature on the subject. Therefore, this review is aimed
at bringing our attention to the radiological implications of
lead use in diagnostic radiology.
USES OF LEAD AND LEAD-BASED MATERIALS IN
DIAGNOSTIC RADIOLOGY
Lead is used in large quantities in X-ray apparatus for
different purposes in diagnostic radiology. Lead readily
absorbs radiation and is used in many forms and
et
al.
57
thicknesses in the field of radiation protection. A good
example is a lead apron. A lead apron is a protective
garment that is designed to shield the body from harmful
radiation, usually in the context of medical imaging
(Ngaile et al., 2008). Both patients and medical personnel
wear these aprons, which are customized for a wide
range of usage (Ngaile et al., 2008). Lead aprons also
vary in lead equivalence; a lead equivalence of 0.5 mm
recommended in the safety codes limits the x-ray
transmission through the lead apron to less than 10% at
150 kVp. At 70 kVp, this apron would provide greater
15
protection, limiting the transmission to less than 1%.
Lead is also a major component of structural facilities
used in the design of diagnostic radiology departments
(Ngaile et al., 2008; Hohl et al., 2005).
Other important uses of lead of radiological significance
include but not limited to the following, ranging from
minor x-ray accessories to the main x-ray equipment
itself; some x-ray cassette covers, grid interspacing
materials, gonad shields, lead gloves, skirts, vests, lead
goggles and other shield materials such as lead-lined dry
walls, lead angles, lead lined plywood, lead bricks, doors
and frames, x-ray glass window and frames and the x-ray
tube housing itself is made up of 2 mm of lead (Ngaile et
al., 2008).
EFFECTS OF LEAD IN THE BODY
The negative effects of lead in the body is widely
documented in the literature (Alkhatib et al., 2014; Liao et
al., 2016). Lead taken internally in any form is highly
toxic; the effects are usually felt after it has accumulated
in the body over a period of time (Alkhatib et al., 2014;
Abadin et al., 2007).
Lead serves no useful purpose in the human body but
its presence in the body can lead to toxic effects
regardless of exposure pathway. Lead can get into the
4
body when an individual inhales lead dust, fume or mist.
Lead is not absorbed through the skin except in cases of
some organic lead compounds such as tetraethyl lead
and tetramethyl lead found in petrol (Chung et al., 2008).
With prolonged exposure, the amount of lead
accumulation in the body increases. Once absorbed into
the body, lead can cause both immediate and prolonged
health effects (Alkhatib et al., 2014; Liao et al., 2016).
Possible health implications of excessive lead exposure
as reported by literature include but are not limited to the
following;
Headaches
Tiredness
Irritability
Constipation
Nausea
Stomach pains
Anemia
58
Sky. J. Med. Med. Sci.
Loss of weight
Far more serious consequences such as kidney damage,
nerve and brain damage may result from continued
exposure (Lim et al., 2015). Particularly at risk of lead
exposure is the developing unborn child, especially in the
early weeks, before pregnancy becomes obvious.
Research evidence has shown that in young children,
lead poisoning may cause permanent damage to the
central nervous system and reduced intellectual
capabilities (Abadin et al., 2007).
It is also a very dangerous poison, particularly for
children (Abadin et al., 2007), when it is accidentally
inhaled or ingested. There is also convincing evidence
that lead appears to have no toxicological threshold
(Prüss-Üstün and Corvalán, 2006).
DISPOSAL
OF
OUT-OF-USE
LEAD-BASED
MATERIALS IN DIAGNOSTIC RADIOLOGY AND
PUBLIC HEALTH CONCERNS
The effects of lead poisoning have been known since
ancient times. In 200 BC the Greek physician Dioscorides
observed that “lead makes the mind give way.” (Roberts
et al., 2001). Until the beginning of the 20th century, lead
poisoning was viewed largely as an occupational disease
of adults (Liao et al., 2016). In the 1890s, lead paint
poisoning in children was first recognized, and childhood
lead poisoning is now well documented and persists as a
major public health problem throughout the world (PrüssÜstün and Corvalán, 2006; Liao et al., 2016). Childhood
lead poisoning continues to be a major public health
problem for certain group of children, specifically lowincome, urban, African-American children in the United
States (Roberts et al., 2001), children suffering from
abuse and neglect (Chung et al., 2001), children living in
rural mining communities (Lynch et al., 2000) and
children in developing countries (Falk, 2003; Fewtrell et
al., 2004; Prüss-Üstün and Corvalán, 2006).
It has been estimated that 99% of the lead that enters
the adult human body and 33% that enters a child’s body
are excreted in about two weeks. Therefore, lead
poisoning is of much concern in children because they
are susceptible to developmental delays secondary to
lead toxicity (Alkhatib et al., 2014).
Although, lead does an excellent job of blocking out
radiation, it can be harmful to the environment and public
health if not properly disposed of (Falk, 2003; Fewtrell et
al., 2004). Lead has a tendency to accumulate into the
environment, having long residence time compared with
most pollutants. It can as well remain accessible to the
food chain and human metabolism far into the future
(Orisakwe et al., 2014). In advanced countries, lead
disposal strategies are in place with proper regulations.
For example, in Canada, lead is included in the toxic
Substances list, under the Canadian Environmental
Protection Act (CEPA) Registry. Hence, it is
recommended that it should not be disposed of as
conventional garbage but as hazardous wastes.
Responsible officers are assigned for disposal of such
wastes for various organizations (ATSDR, 2000). This
practice is rare in the radiology department of most
developing countries (Daniel and Matthew, 2014).
Lead-based materials such as x-ray equipment and
accessories have found varied applications in diagnostic
radiology over the years. This is though, more critical in
the aspect of lead shielding (Ngaile et al., 2008; Hohl et
al., 2005). However, the problem arises when this
equipment and accessories have exhausted their
usefulness and are due for disposal, they constitute a
major challenge. This is even more serious in low-income
countries (Daniel and Matthew, 2014). For example, lead
sheets used in shielding or lead lining of the walls of
diagnostic x-ray rooms and lead aprons or gonadal
shields could peel off from the walls or decompose to
form lead oxide which is highly toxic (Liao et al., 2016)
and hence, becomes a public health threat (Alkhatib et
al., 2014; Prüss-Üstün and Corvalán, 2006). While there
are regulatory guidelines for recycling and disposal of
most of these materials in developed countries, this
remains a nightmare in most developing countries
because regulatory policies on lead use in health care
settings are sparse Fewtrell et al., 2004; Daniel and
Matthew, 2014). The use of lead-based materials have
been highly minimized and in most cases, eliminated in
developed countries Liao et al., 2016). The benefits of
proper out-of-use lead disposal from diagnostic radiology
are enormous as consequent reductions in environmental
pollution will not only benefit households, but also
fisheries, the food industry, those engaged in waterbased recreational activities, as well as the health sector
(from avoided healthcare costs), and the labour sector
(from fewer work days lost to illness) Prüss-Üstün and
Corvalán, 2006). The focus of most studies on use of
lead and its associated hazards have been on
households paints, mining, industrial and other
applications (Prüss-Üstün and Corvalán, 2006; Fewtrell
et al., 2004) (Alkhatib et al., 2014; Mielke, 2002; Fewtrell
et al., 2004). Less emphasis has been placed on medical
applications of lead especially in diagnostic radiology and
its concomitant public and environmental health
implications during disposal (Daniel and Matthew, 2014).
Conclusion
This review has put into perspective an important but
often neglected area of research on the use of lead in
diagnostic radiology. Out-of-use lead sources from
diagnostic radiology could pose a threat to public and
environmental health if not properly disposed of. There is
need for further empirical studies on lead-based wastes
generated in radiology and disposal strategies adopted
Nkubli
by hospitals.
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