Assessment of dna damage in coal open-cast mining workers using the cytokinesis-blocked micronucleus test and the comet assay
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / s c i to t e n v
Assessment of DNA damage in coal open-cast mining workers using thecytokinesis-blocked micronucleus test and the comet assay
Grethel León-Mejía Lyda Espitia-Pérez , Luz Stella Hoyos-Giraldo , Juliana Da Silva ,Andreas Hartmann , João Antônio Pêgas Henriques ,, Milton Quintana a Laboratorio de Investigación Biomédica y Biología Molecular, Universidad del Sinú, Montería, Córdoba, Colombiab Department of Biology, Research Group Genetic Toxicology and Cytogenetics, Faculty of Natural Sciences and Education, Universidad del Cauca, Popayán, Cauca, Colombiac Laboratorio de Genética Toxicológica (PPGGTA), Universidade Luterana do Brasil (ULBRA), Canoas-RS, Brazild Novartis Pharma AG, Basel, Switzerlande Departamento de Biofísica, Instituto de Biociências, Universidade Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil
Coal mining is one of the most important causes of environmental pollution, as large quantities of coal dust
particles are emitted. Colombia-South America has large natural coal reserves and “El Cerrejón” is the world's
largest open-cast mine located in the northern department of Guajira. The aim of the present study was to
evaluate genotoxic effects in a population exposed to coal residues from the open-cast mine “El Cerrejón”. 100exposed workers and 100 non-exposed control individuals were included in this study. The exposed group
was divided according to different mining area activities: (i). Transport of extracted coal, (ii). Equipment field
maintenance, (iii). Coal stripping and, (iv). Coal embarking. Blood samples were taken to investigate
biomarkers of genotoxicity, specifically, primary DNA damage as damage index (DI), tail length and% of tail
DNA using the Comet assay (alkaline version) and chromosome damage as micronucleus (MN) frequency in
lymphocytes. Both biomarkers showed statistically significantly higher values in the exposed group comparedto the non-exposed control group. No difference was observed between the exposed groups executingdifferent mining activities. These results indicate that exposure to coal mining residues may result in anincreased genotoxic exposure in coal mining workers. We did not find a correlation between age, alcoholconsumption and service time with the biomarkers of genotoxicity. Our results are the first data of genotoxiceffects induced by coal mining exposure in Colombia, and thus, contribute to the exploration of test batteriesuse for monitoring of exposed populations and may stimulate designing control, hygiene and preventionstrategies for occupational health risk assessment in developing countries.
2010 Elsevier B.V. All rights reserved.
caloric power of this mineral, when it is exposed to ambient oxygenand sunlight a spontaneous combustion process may be initiated
Coal is one of the most abundant minerals in nature and it
which liberates large amounts of Polycyclic Aromatic Hydrocarbons
constitutes the largest fossil fuel source used for the generation of
(PAHs) into the environment. Coal residues consists of a mixture of
energy. However, its extraction and use constitute an important
substances, containing carbon, hydrogen, nitrogen, oxygen and sulfur
pollution factor which represents a major threat for human health and
(mineral particles of smaller size and inorganic
extraction large quantities of particles of coal dust are emitted
Colombia in South America has one of the world's largest natural
contributing to environmental pollution. In addition, due to the high
coal reserves in Latin America and “El Cerrejón” is the world's biggestopen-cast mine located in the northern department of Guajira (The main operations carried out in this mine are: stripping
⁎ Corresponding authors. Quintana is to be contacted at Laboratorio de Investigación
(extraction of coal) and crushing (mincing of coal for transporting).
Biomédica y Biología Molecular, Universidad del Sinú, Campus Elías Bechara Zainúm,Calle 38 Cra.1W Barrio Juan XXIII, Montería, Córdoba, Colombia, South America. Tel./
During the extraction processes in coal open-cast mining, particulate
fax: + 57 4 7841961. Henriques, Departamento de Biofísica, Prédio 43422, Laboratório
matters and combustion products are released into the atmosphere,
210, Campus do Vale, Universidade Federal do Rio Grande do Sul, Avenida Bento
where they constitute complex mixtures (These
Gonçalves 9500, Bairro Agronomia-CEP 91501-970, Porto Alegre, RS, Brazil. Tel.: +55
mixtures are considered hazardous due to synergistic, additive and
0048-9697/$ – see front matter 2010 Elsevier B.V. All rights reserved. doi:
G. León-Mejía et al. / Science of the Total Environment 409 (2011) 686–691
The predominant route of coal mining residues exposure is
Exposed workers were matched to non-exposed controls by age
through inhalation. Today it is known that chronic inhalation of
(±2 years) and similar social-economic status. Confounding and
complex mixtures, containing substances such as heavy metals, ash,
exclusion factors were collected from all participants who responded
iron, PAHs and sulfur, can result in lung disorders including simple
to an interviewer-administered, detailed, standard questionnaire
pneumoconiosis, progressive massive fibrosis, bronchitis, loss of lung
which included data of health status, cancer history, other chronic
diseases, lifestyle, nutrition, smoking habits, medication intake, and
Recent studies have postulated that some of
frequency of alcohol consumption (total number of drinks and the
these diseases may be a consequence of inhaling such material
most widely alcoholic beverages consumed), occupational and time of
resulting in activation of macrophages, interaction with epithelial
service, protective measures, and previous exposure to medical X-rays
cells and other cells, finally leading to generation of oxidative stress
or treatment with known carcinogens. All individuals included into
). Besides direct cellular damage, compounds
the study were non-smokers. The exposed group was selected
released by coal mining activities such as PAHs present an important
according to the following inclusion approaches: voluntary accep-
mutagenic hazard that has been associated with an increased risk for
tance, been healthy and time of service ≥5 years. Exclusion criteria for
exposed and non-exposed groups were age over 60 years or less than
findings, coal dust remains classified as non carcinogen for human
24 years, smoking (current and ex-smoking habits), medical treat-
(Group 3) in International Agency for Research on Cancer (
ment up to 3 months or X-ray up to 1 year before sampling and
therapeutic drugs intake, known to be mutagenic. All data was
Biomonitoring studies in peripheral lymphocytes of coal workers
organized and recorded in databases. There are no major differences
demonstrated increased adduct formation and increased of non-
regarding social-economic status or dietary habits were identified.
cellular and cellular sources of reactive oxygen species that can induce
The whole study population was informed about the aim, benefits,
risks and methodology details of the study though the informed
There are only a few studies on the occupational hazard effects in
consent, which was obtained from all individuals. We previously had
coal miners. However, some studies have been conducted in animals
the approval of the University of Sinú Ethic Committee for this
of mining regions. For example, cytotoxic and genotoxic effects of coal
research study. All the information identifying the study individuals is
dust have been evaluated in vivo in wild rodents in coal mining areas
kept at the “Laboratorio de Investigación Biomédica y Biología
Molecular” of the University of Sinú in the city of Montería, Cordoba
The aim of the present study was to evaluate potential genotoxic
department, which is the only institution having full identifiable
effects in peripheral blood lymphocytes in an exposed population to
coal residues in the open-cast mine “El Cerrejón” in Guajira-Colombiausing Comet assay and Micronucleus (MN) test. The results obtained
from this study present the first data for Colombia on a genotoxichazard generated by coal mining residuals exposure. In addition, our
After informed consent was obtained from each individual,
data represent an assessment of the feasibility of using tool
peripheral blood samples from all 200 individuals were collected by
biomarkers for evaluating potential occupational health risks. An
venipuncture. 20 mL of blood were drawn into heparin tubes (Becton
area of application of such methods is to investigate whether it can be
Dickenson, vacutainer) for the Comet assay and MN test. All blood
applied in coal mining activities in Colombia to support efforts for
samples tubes were coded and kept in upright position at room
applying cleaner production procedures which would have less
temperature in dark during the transportation overnight to the
negative impacts on the environment and the human population.
laboratory, where the samples were processed immediately uponarrival.
The Comet assay in the present study was carried out according to
the original methodology (alkaline version) described by
The exposed individuals included in this study were workers from
“El Cerrejón” open-cast coal mine, in Guajira Department in the north
coast of Colombia, South America. A group of 100 exposed individuals
lymphocytes by Histopaque 1077, were mixed with 270 μL 0.5% of
engaged in surface activities of the sub-bituminous open-cast coal
low melting point (LMA-Invitrogen) at 37 °C. This mixture was placed
mine with a minimum time of service of 5 years were selected. The
into a slide previously coated with 1.5% of normal melting point
non-exposed control group consisted of 100 individuals, from Guajira
agarose (NMA-Cambrex Bioscience Rockland) processed at 60 °C. The
department, with no known exposure to genotoxic agents including
agarose layers were covered with a cover slip and after gel solidifying
coal, radiation, chemicals or cigarettes. Both study populations
the cover slips were removed. The slides were immersed overnight in
(exposed and non-exposed group) lived in the same region
lysis solution (2.5 M NaCl, 100 mM EDTA and 10 mM Tris, pH 10.0–
considering that the two populations should have the same genetic
10.5, 1% with freshly added 1% Triton X-100 and 10% DMSO) at 4 °C in
background and the same life habits.
dark. Afterwards, the slides were placed for 30 min in alkaline buffer
The exposed group was divided according to the engaged activities
at 4 °C (300 mM NaOH and 1 mM EDTA, pH N 13) to unwind the DNA.
in the mine: (i) Extracted coal transport (n = 50) in which the workers
The alkaline electrophoresis was carried out for 30 min at 25 V and
are involved in coal transport up to the arrival in the storing centers.
300 mA. This standard alkaline procedure allows single-strand DNA
(ii) Equipment field maintenance (n = 18) these workers drive trucks
breaks to be detected and alkali labile lesions (i.e., apurinic/
to spread water in the roads where large quantities of coal dust are
apirimidinic sites) are converted to strand breaks under these
generated the workers also fix the coal extraction equipment. (iii)
conditions as well. The gels were neutralized with 0.4 M Tris (pH
Coal stripping (n = 17) these workers are engaged in coal stripping
7.5) with 3 washes of 5 min each. Finally, the slides were stained with
activities and the accumulation of the material for the transport in
50 μL ethidium bromide (2 μL/mL) and examined at 40× magnifica-
trucks, they also extinguish fires generated by coal spontaneous
tion under a fluorescence microscope equipped with a green filter of
combustion. (iv) Coal embarking (n = 15) these workers are involved
540 nm. Direct light exposure of the samples was avoided during the
in shipping of coal in containers to be exported to other countries.
whole process. For each individual we analyzed 100 randomly
G. León-Mejía et al. / Science of the Total Environment 409 (2011) 686–691
selected Comets (50 cells from each of two replicate slides). For the
analysis of the images we used a system image analysis software and
Main demographic characteristics of the studied population: non-exposed control andexposed groups.
the considered endpoints as measurement to quantify DNA damage,were tail length and % of tail DNA. In addition, the cells were classified
according to tail size into five classes ranging from undamaged (0) to
maximally damaged (4), obtaining a measure of the individual
damage for each animal and consequently for each analyzed group.
The damage index (DI) calculation was carried out according to the
visual classification system (). The values for the
damage index could range from 0 (100 cells class 0) up to 400 (100
cells class 4). For the statistical analysis we took into account the meanvalues for all the Comet assay parameters.
⁎ Drink more than three beers/day or drink in excess of once a week.
The MN test using the cytokinesis-block technique was performed
deviation (SD) of the exposed group was 17.7 ± 6.9 years (range, 5–
This approach allows reliable data scoring
shows the percentage of alcohol consumption for non-
because only the MN of those cells that have completed one nuclear
exposed group (45%) and exposed group (55%), considered as alcohol
division are analyzed. Cultures were prepared with whole blood in
consumer that drink more than three beers per day or drink in excess
duplicate and processed as described by .
Heparinized whole blood (0.5 mL) was added to 4.5 mL of RPMI
summarizes the Comet assay data and Micronucleus
1640 medium (Sigma R8758, USA) supplemented with 2 mM
frequency values for both study groups. The mean values of both
glutamine (Sigma A5955,USA), 10% fetal bovine serum (Gibco/
biomarkers parameters in the exposed group demonstrated signifi-
Invitrogen 15000-044, Brazil), 100 μL/mL antibiotic–antimycotic
cant differences when compared to the values of the non-exposed
(Sigma A5955, USA) and 2% phytohemaglutinin (Sigma L8754, USA)
control group (p b0.001), which were analyzed using Kruskal–Wallis
to stimulate the lymphocytes. Cultures were incubated at 37 °C in
test (Dunn correction). There was no statistically significant differ-
ence between the four different coal mining activities (p N 0.05).
2 in a humidified atmosphere. Two parallel
cultures were set in tubes (Falcon 3033) for each sample. Cytocalasin
The results obtained in Micronucleus frequency show that the
B (Sigma, C6762) was added at 44 h of incubation at a final
values in the exposed to coal mining residuals group (8.6 ± 4.8) are
concentration of 6 μg/mL. The cells were harvested at 72 h, treated
higher compared with the non-exposed control group (2.9 ± 4.0). The
with hypotonic solution (0.075 M KCl) immediately centrifuged and
differences were significant as is shown in evaluated through
fixed three times with methanol/acetic acid (3:1). The fixed cells were
Mann Whitney U-test (p b 0.001).shows the mean values of
dropped onto humidified slides and air dried slides were stained with
the Comet assay parameters of the two study groups. This compar-
Giemsa for 10 min. MN registration was performed on coded slides
ison, for each Comet assay parameter damage index, tail length and%
with double blind. Two thousand binucleated cells (BN) per individual
of tail DNA, clearly demonstrates higher levels of DNA damage in the
(1000 BN per culture) were registered. All coded slides were analyzed
exposed group (mean tail length = 23.4 ± 6.5; mean% of tail
with an optical light microscope (40× magnification). All slides were
DNA = 13.1 ± 7.9; mean DI = 60.0 ± 39.5) compared to the non-
scored by one reader blinded to the exposure status of the individuals.
exposed control group (mean tail length = 14.3 ± 2.5; mean% of tail
The scoring criteria followed those proposed by
DNA = 2.9 ± 1.5; mean DI = 9.0 ± 6.4). These differences were allstatistically significant evaluated using Mann Whitney U-test(p b 0.001).
The Spearman correlation coefficients for MN frequency with age,
and DNA damage (tail length, % of tail DNA, DI) for non-exposed
The normality of the variables was evaluated using the Kolmo-
control and exposed groups were not significant (p N 0.05). The
gorov–Smirnov test; χ2 and t-tests were used to compare the
correlations between MN frequency with time of service, and DNA
demographic characteristics of study populations. The statistical
damage (tail length, % of tail DNA and DI) for the subdivided exposed
analysis of differences in MN test and DNA damage measured by
groups, were not significant (p N 0.05). We analyzed the effect of
Comet assay were carried out using the non-parametric Mann
alcohol consumption on MN frequencies and DNA damage in all
Whitney U-test and statistical differences between the five groups
groups using Mann Whitney U-test and found no difference in any of
(non-exposed control, extracted coal transport, equipment field
maintenance, coal stripping, and coal embarking) were analyzedusing the non-parametric two-tailed Kruskal–Wallis test with the
Dunn correction for multiple comparisons to perform a non-parametric analysis of variances. Correlations between different
Occupational exposure to coal residues is a public health concern
variables were determined by Spearman rank correlation test as
in developing countries owing to the lack of regulation policies and
appropriate. The critical level for rejection of the null hypothesis was
epidemiologic surveillance programs and to the limited coal combus-
considered to be p value of 5%. All analyses were performed with the
tion residues and particulate matter emission management
PRISMA 5.0 statistical software package.
During coal open-cast miningextraction processes significant amounts of these substances are
released to the atmosphere where they constitute complex mixtures(). The main route of exposure to these particulate
The main demographic characteristics of the study population are
matters is through inhalation. Most of the published studies have
shown in . The mean age of exposed group was 44.0 ± 7.5 years
(range, 24–60 years), and non-exposed control group was 43.7 ±
7.8 years (range, 27–60 years).The mean time of service ±standard
evaluated induction of chromosome aberrations by coal complex
G. León-Mejía et al. / Science of the Total Environment 409 (2011) 686–691
Table 2Comet assay and Micronucleus test parameters in non-exposed control and Exposed group divided by work areas activities (mean ± standard deviation).
⁎ Significant difference in relation to the non-exposed control group; Kruskall Wallis–Dunn correction pb0.001.
mixtures in open-cast mining workers. Colombia possesses the largest
matrix components. The formation and degradation of extracellular
coal reserves in Latin America (however, to date,
matrix may also be affected by ROS, as well as proteases and
genotoxic endpoints related to coal open-cast extraction has only
antiproteases produced by the various cell types present in the
surrounding tissue ). When there is excessive
In the present study we investigated potential genotoxic effects of
production of ROS, or when there are insufficient in vivo defense
coal exposure in mining workers. Biological monitoring of exposure to
mechanisms, oxidative stress may occur. This stress may result in DNA
chemical substances in the workplace is crucial to assess potential
damage, lipid peroxidation, protein modification, membrane disrup-
human health risks, as an integral strategy to improve occupational
tion, and mitochondrial damage ), all modifications
health, safety conditions and life quality in developing countries. We
capable of affecting cytogenetic damage levels.
applied the Comet assay to compare the extent of primary DNA
Other components associated to heavy metals toxicity such as
damage and the Micronucleus test as cytogenetic effect biomarker in
Copper, Lead, Cadmium, Nickel, Vanadium and Zinc appear in high
peripheral blood lymphocytes from exposed and non-exposed
concentrations in coal complex mixture (Large
amounts of mutagenic compounds such as PAHs are produced during
Our results demonstrate that the group exposed to coal mining
the spontaneous coal combustions which is a common process in coal
residuals exhibited a significantly higher extent of DNA damage in
storing centers due to environmental factors as sunlight and climate
peripheral lymphocytes in the Comet assay and MN test compared to
conditions. Some PAHs related to coal mining such as chrysene and
the control group. Previous studies with underground coal mine
benzo(k)fluoranthene are indicators of coal combustion, and pyrene
workers have demonstrated higher levels of chromosomal damage,
and fluoranthene are associated with such processes ). PAHs
evaluated through chromosomal aberration, MN and sister chromatid
can induce DNA lesions as single-strand breaks via DNA repair
). There are no significant differences in
) and electrophilic metabolites that covalently interact with the
DNA damage average (Comet assay and MN test) of control group
were detected between this study and previous studies of our group
with purines, especially with guanine after metabolic activation by
It is known that coal mining activities release significant quantities
Due to the complex mixture in occupational coal mining environ-
of fugitive particles and toxic gases as sulfur dioxide into the
ments it is difficult to relate genotoxic effects to a specific agent or
environment ). Some quality parameters of coal from
compound. The Comet assay is particularly sensitive towards the
the open-cast mine “El Cerrejón” are total moisture (~10%), volatiles
detection of direct and indirect DNA strand breakage and DNA
(~30%), ash (~8%), sulfur (~1%), carbon (~ 70%), hydrogen (~6%),
alkaline-labile sites. These types of DNA damages are usually induced
oxygen (~ 5%), nitrogen (~1%), as well as different metals
by most of the genotoxic agents which induce DNA breaks at the
phosphodiester skeleton or between bases and sugars resulting in
coal complex mixture release into the atmosphere ()
abasic sites (The MN assay in peripheral blood
constitute one of the most important occupational health and safety
lymphocytes is extensively used in biomonitoring and molecular
risks of workers due to the potential synergistic toxic effects of this
epidemiology studies to evaluate the presence and the extent of
chromosomal damage in exposed human populations to genotoxic
has suggested that reactive oxygen species (ROS) and their products
agents, and also because an increased MN frequency has been
are involved in the pathogenesis of lung disorders and cancer risk
validated as a cancer risk biomarker in humans (
exposed workers. The primary target cells of inhaled coal dust
In our study no significant difference in markers of genotoxicity
particles are macrophages and epithelial cells. Activated macrophages
between the four coal mine activities (extracted coal transport,
(phagocytosis toxicity) produce excessive amounts of ROS and
equipment field maintenance, coal stripping and coal embarking) was
cytokines. ROS may additionally be generated via cell-independent
observed. These observations indicate that exposed workers have a
mechanisms due to intrinsic chemical properties of the coal dust (e.g.
comparable genotoxic response to complex mixture exposure
surface radicals and iron). Epithelial cells and fibroblasts which are the
independently to the area and activity in the mine. In addition to
main producers of components of the extracellular matrix including
these findings, there was no correlation between the time of service
collagens, proteoglycans and elastic fibres, are also known to produce
and Comet assay parameters or MN frequency. This observation is in
cytokines and ROS upon stimulation. Additional phagocytotic cells
agreement with the results obtained in other occupational settings
(neutrophils, monocytes/macrophages) may be recruited by chemo-
kines produced by the alveolar macrophages as well as epithelial cells,
In our results, there was no influence of alcohol consumption, age
and may amplify local production of ROS and cytokines. Both ROS and
or time of service in the exposed individuals on Comet assay
cytokines may cause damage or proliferation of local epithelial and
parameters tail length, % of tail DNA and damage index or the MN
mesenchymal tissue and may as such have consequences to lung
tissue morphology, cell turnover and deposition of extracellular
The results obtained with respect the alcohol consumption are in
G. León-Mejía et al. / Science of the Total Environment 409 (2011) 686–691
agreement with other occupational studies in which there was no
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