Mutation Research/Genetic Toxicology and Environmental Mutagenesis
Evaluation of telomere length and genotoxicity among asphalt associated workers
Introduction
Asphalt workers are one of the major occupational groups being exposed to a variety of chemical, biological, or physical (e.g. noise, heat, and radiation) agents throughout their work-life [1]. The bitumen asphalt preparation and road paving tasks chronically expose workers to polycyclic aromatic hydrocarbons (PAHs) both by inhalation and dermal contact [2]. Asphalt is mixtures of bitumen, small stones, sand, and filler primarily used for road paving. Asphalt is also known as bitumen is a dark, semisolid form of petroleum product, a common binder or glue used in road construction and its emulsions are often sprayed onto the road surface before paving [3]. Bitumen contains several chemicals, including polycyclic aromatic hydrocarbons (PAHs), volatile organic compounds (VOCs), and metals. Exposure to PM, VOCs, and various polycyclic aromatic compounds is common among bitumen workers and the level of exposure varies at different steps of processing and road paving. About 93% of inhalable dust emitted during road paving consists of organic particulate matter [4]. The PAHs associated particles with aerodynamic diameters below 10 μm (regarded as PM10) are respirable and can deposit in the human respiratory system [5]. As per WHO, particulate matter is one of the most common indoor and outdoor air pollutants [6].
During paving, hot application of asphalt complex mixtures of aerosols and vapors are emitted which contain carcinogens such as PAHs and other compounds [7,8]. Also, the earlier study confirmed the risk of carcinogen exposure (Benzo(a)pyrene) and carcinogenic hazards among asphalt paving workers [9]. Recently, the International Agency for Research on Cancer (IARC) classified occupational exposures to conventional asphalt and its emissions during road paving as group 2B (possibly carcinogenic to humans) [10]. It has been shown that exposure to asphalt fumes causes DNA damage [1]. The 8-OHdG is considered as major DNA damage caused by reactive oxygen species (ROS) and its formation occurs due to the attack of carbon 8 (C8) in guanine by hydroxyl radicals [11]. The early steps in the development of cancer, mutation, and aging are the result of oxidative damage to the DNA in cells [12].
Telomeres are the tandemly repeated G rich (5′ TTAGGG 3′) nucleotide protein structures at the terminal regions of eukaryotic chromosomes that protect the genetic material of the cells and its dysfunction leads to carcinogenesis in human. [13,14]. Telomere length serves as a biological clock of the living organism and in humans, its length decreases with age. During the normal cellular process, the small portion of telomeric DNA is lost with each cell division [15]. While additional attrition of telomere length shown to be accelerated by oxidative stress, deficient DNA repair capacity [16], environmental and occupational exposure to traffic-related air pollution (i.e. PM, black carbon (BC), benzene and toluene), PAHs, N-nitrosamines, pesticides, lead exposure in car mechanical workshops and hazardous waste exposures [17,18]. The chromosomal end containing telomeric DNA regions is sensitive to the reactive oxygen species (ROS) damage [19]. It has been suggested that telomere attrition might be used for biomonitoring purposes and telomere length may also work as a marker of susceptibility [20].
The first barrier to the inhalation or ingestion of carcinogens is buccal epithelial cells. These cells are capable of metabolizing carcinogens to reactive products. About 90% of human cancers originate from epithelial cells and hence represent a preferred target for early genotoxic events induced by carcinogenic agents [21]. Micronuclei (MN) assay in exfoliated buccal cells is a useful and minimally invasive method for monitoring genetic damage in humans [22]. The earlier studies suggest that MNs and altered telomere length are biomarkers associated with increased cancer risk [[23], [24], [25], [26]]. According to epidemiological studies, there is a poor correlation between bitumen exposure and cancer risk [27,28] but the effects of bitumen exposure on health shouldn’t be ignored.
Therefore, the present study intended to assess the genotoxic hazards associated with exposure to asphalt fumes, particulate matter, engine exhaust, and passing traffic exposure by monitoring workplace ambient PM10, oxidative stress (8-OHdG), relative TL, and cytogenetic damage (MN) among asphalt related workers. As per our knowledge, this is the very first study evaluating the effect on telomere length amongst Indian asphalt workers.
Section snippets
Study area and subjects
The study has been carried out in and around Bangalore city, India. Before the initiation of the study, a survey was completed to identify asphalt mixing plants, and the importance of the study was explained to the plant operators. Overall 107 study participants, including 54 exposed group (45 male, 9 female) and 53 unexposed control group (41 male, 12 female), were enrolled in a present case-control study. The study has obtained ethical clearance from the institutional ethical committee. The
Demographic and health complaints status
The basic characteristics and self-reported health complaints of study participants are illustrated in Table 1. The total out of 107 participants, both male and female participants were equally distributed in the exposed and unexposed control group. The mean age of the exposed group was 29.6 + 8.0 years and the control group was 30.7 ± 7.9 years. The exposed group has 5.5 ± 5.2 years of experience with 8 ± 0.9 h of work time per day. It was observed that only 42.6% of the exposed group was
Discussion
Worldwide, there is underprivileged concern about the risk of malignancy due to bitumen exposure. Also, only limited evidence exists on the genotoxic risk of occupational exposure to asphalt, especially in India. Asphalt associated workers are exposed to asphalt fumes, particulate matter and engines exhaust through an inhalation route. Exposure to particulate matter, volatile organic compounds, and various polycyclic aromatic compounds are common among bitumen workers [4].
The present study
Conclusion
The occupational environment in asphalt related work poses a significant risk of adverse health effects and genetic damage in workers. This health risk might be reduced by the use of adequate personal protection equipment. The increases in 8-OHdG levels and buccal cell MN frequencies, as well as the reduction in leukocyte relative telomere length observed in this study among asphalt workers, suggest that asphalt-related occupational exposure is correlated with genetic damage. The types of
Declaration of Competing Interest
The authors declare that there are no conflicts of interest.
Acknowledgements
We are thankful to the Director, ICMR-National Institute of Occupational Health, Ahmedabad for approving the project to carry out and technical staff of ROHC(S), Bangalore for their support in field and laboratory work. We are thankful to Dr. Ashok Kuppuswamy from Invitrogen, Applied Biosystems for his help in Telomere length assay set up and optimization. We are thankful to NIV, Bangalore field unit for providing ELISA facility and NIMHANS, Bangalore for providing a DNA quantification
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2021, Mutation Research - Genetic Toxicology and Environmental MutagenesisCitation Excerpt :All of them observed increase in DNA damage, including correlations among TL and MN and NPB [56], and of blood Pb levels with MN [85]. Moreover, other four studies evaluated oxidative stress statuses in the studied groups [57,59,84,118]. Data on oxidative stress vary among the industries assessed.
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