EPIGENETIC EFFECTS OF MATERNAL POLYCYCLIC AROMATIC HYDROCRABONS EXPOSURE: A SYSTEMATIC REVIEW ON DNA METHYLATION ALTERATIONS AND DISEASE SUSCEPTIBILITY

Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [486] EPIGENETIC EFFECTS OF MATERNAL POLYCYCLIC AROMATIC HYDROCRABONS EXPOSURE: A SYSTEMATIC REVIEW ON DNA METHYLATION ALTERATIONS AND DISEASE SUSCEPTIBILITY Leighanna Ryielle B. Blanco1 John Paul C. Casintahan1 Albert Jommel S. De Leon1 Kristale Mae E. Laquindanum1 Carl Anthony A. Orcales1 Gecelene C. Estorico1,2 Civil and Allied Department; Environmental Science and Chemical Technology Department 1Technological University of the Philippines – Taguig, Metro Manila, 1630, Philippines 2De La Salle University – Dasmariñas, Cavite, DBB-B, 4115 West Ave., Dasmariñas ABSTRACT Polycyclic aromatic hydrocarbons (PAHs) are common environmental pollutants formed primarily during incomplete burning of fossil fuels and organic matter. In addition to their known carcinogenic and mutagenic actions, the current literature points to the fact that they can change the human epigenome, especially by modifying the DNA methylation patterns, which can predispose one to disease. The systematic review summarizes the recent cohort and birth studies examining the effects of prenatal and environmental toxicity to PAHs on DNA methylation of placental and cord blood samples. A number of studies found that there were significant correlations between exposure to PAH metabolites, including 1-hydroxynaphthalene, 2-hydroxyfluorene and 1hydroxypyrene, and differentially methylated CpG sites of transcriptional regulation, cellular transport, and DNA repair genes, including ZNF354C, CCDC63 and MFSD2A. The identification of the functional pathway showed that there is enrichment in the pathway of lipid metabolism, oxidative stress response, and ferroptosis, which indicated that these methylation changes could disrupt the placental performance and fetal growth. In addition, the results of the mother-infant cohort studies showed that increased prenatal exposure to PAH was associated with reduced global DNA methylation in cord blood, which represents a potential impairment of methylation maintenance in pregnancy. On the other hand, the high levels of benzo [a] pyrene-DNA adducts were associated with localized hypermethylation which could indicate compensatory or repair-related processes. As a whole, the analyzed data points to the fact that the placenta is an epigenetic portal between maternal exposure to PAH and fetal molecular programming that leaves permanent traces that can predispose to adult metabolic, respiratory, and neurodevelopmental disorders. These results highlight the importance of DNA methylation as a mechanistic linkage between exposure to the environment and risk of disease and the necessity to undertake longitudinal and mechanistic studies to elucidate causality and establish possible biomarkers of early prevention. Keywords: CpG sites, Environmental biomarkers, Fetal programming, Oxidative stress, Prenatal exposure INTRODUCTION Polycyclic Aromatic Hydrocarbons (PAHs) are poisonous substances formed as a result of the incompleteness of the burning of organic substances containing coal, oil, gasoline, wood, or tobacco. These pollutants are present nearly everywhere including the air due to vehicle exhausts as well as industrial emissions, on soil and even in charred or grilled food thus human exposure is nearly unavoidable. PAHs have the potential to be very dangerous as they accumulate in the environment and therefore, when they find their way into living tissues. Chronic exposure has been linked with cancer, heart diseases, respiratory issues, and developmental abnormalities (Montano et al., 2025). Historically, PAHs were believed to act primarily by a direct damage to DNA including Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [487] the establishment of PAH-DNA adducts capable of causing mutations. Nevertheless, it has recently been demonstrated that the PAHs are also capable of disrupting the process of epigenetic regulation, specifically DNA methylation, that is a significant factor in driving gene activity (Rider et al., 2019; Li et al., 2018). DNA methylation is either a switch that activates or deactivates genes and this is associated with the addition of a small chemical tag known as a methyl group. Such processing may be impaired, allowing the silencing of important protective genes, or allowing the activation of harmful genes, which puts an individual at risk of disease. Recent work to date points out that the developing fetus in a pregnant woman that is exposed to PAHs (via breathing in contaminated air, smoking, or consuming contaminated food) may be impacted by these epigenetic. Prenatal exposure has been identified as associated with changes in DNA methylation of cord blood and placental tissue which may have an effect on fetal growth, immunity, and neurodevelopment (Latifi et al., 2024; Rider et al., 2019). An example is that high concentrations of maternal PAH exposure have been timbered to cause alterations in genes engaged in inflammation and oxidative stress that could pose the children to illnesses later in life. A range of research indicates also that these first-month exposures can cause epigenetic aging where the biological age of cells is observed to be more than it should be, which makes them more vulnerable to developing chronic illnesses (Li et al., 2018; Campisi et al., 2023). These accumulating findings do not indicate a consistent pattern of results, given that measures of exposure to PAH (air checking vs. urinary biomarkers), the biological sample under study (blood vs. placenta, or sperm), and the methods applied to analyze the databases (e.g., Illumina 450K vs. EPIC arrays) vary (Alhamdow et al., 2020). Such differences make it hard to identify the most important alterations in methylation that contribute to the development of the illness. Due to these gaps, the systematic review and synthesis of current studies that reveal the presence of the consistent epigenetic footprints of PAH exposure have the strong need. The elucidation of the most affected genes and pathways and the impact of the methylation changes on disease susceptibility can be used by the researchers in creating biomarkers of exposure and health risk, enhance environmental risk measures, and assist in making more robust policies on health to minimize human exposure to PAHs. OBJECTIVES The main objective of the study is to conduct a systematic review and synthesize literature on the association between human and maternal exposure to Polycyclic Aromatic Hydrocarbons (PAHs) and the change in DNA methylation patterns, and to determine the role of these epigenetic changes in predisposing different populations to disease. In particular, this study will summarize and evaluate peer-reviewed articles, which examine the relationship between exposure to PAH, especially, at maternal and prenatal stages, and genome-wide or genespecific DNA methylations in humans. It also attempts to define and describe which genes, CpG sites and molecular response alter markedly in response to PAH exposure focusing on potential exposure and effect biomarkers of epigenetic change. Moreover, the systematic review aims to examine and discuss the associations between the changes in the DNA methylations as induced by PAH with the emergence or the development of the major human diseases, such as cancer, cardiovascular, respiratory, metabolic, and developmental disorders induced by maternal exposure. Finally, it will critically review the methodological rigor, strengths, and limitations of literature on the topic, and will offer future research directions to expand the knowledge about PAH-related epigenetic processes in human and prenatal health. METHODOLOGY The study utilizes a systematic methodology made up of three basic elements: Input, Process, and Output. The Input stage entails collecting appropriate and credible information from peer-reviewed journals, scientific databases, and research articles addressing the association between Polycyclic Aromatic Hydrocarbon (PAH) exposure and DNA methylation patterns linked with disease susceptibility. The Process stage involves rigorous screening, selection, and analysis of studies according to PRISMA 2020 standards to ensure methodological reliability and transparency. This involves classification of data according to methylation types, population groups, and exposure levels to determine persistent epigenetic effects. The Output finally offers an integrated synthesis of results, indicating epigenetic changes, biological pathways, and health implications associated with exposure to PAH. This organized framework provides a thorough and evidence-based framework for interpreting the molecular mechanisms linking environmental contaminants to disease susceptibility. Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [488] Figure 1. IPO Diagram of the Study Search Strategy This systematic review adhered to the PRISMA 2020 guidelines to make it transparent, reproducible, and scientifically rigorous in study selection and analysis. An extensive search was made in PubMed, ScienceDirect, and Google Scholar with publications between 2015 and 2025. The primary search keywords employed were “Maternal Exposure,” "Polycyclic Aromatic Hydrocarbons," "PAH exposure," "DNA methylation," "epigenetic modification," and "disease susceptibility." Boolean operators AND and OR were used to narrow down search results and encompass both human and animal studies on the epigenetic effect of PAHs. Moreover, reference lists of included studies were also searched manually for any further relevant studies which were not picked up by the initial search. Inclusion and Exclusion Criteria To guarantee the inclusion of high-quality and relevant literature, certain inclusion and exclusion criteria were used during selection. Studies were considered if they (1) were published from 2015 to 2025, (2) were in English, and (3) investigated the association between PAH maternal exposure and DNA methylation patterns of disease susceptibility or biological aging. Both experimental and epidemiological studies were considered as long as they had measurable DNA methylation results. Review papers, commentaries, conference abstracts, and editorials without original research data were not included in the review. Studies with no direct PAH exposure data, inadequate methylation analysis, or missing results were also not included. Screening and Selection Process All studies identified were organized and managed using a reference management tool, with duplicates automatically removed. Five reviewers independently screened the titles and abstracts to assess their preliminary Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [489] eligibility against inclusion criteria. Full-text screening was conducted to evaluate the methodological quality and relevance of each study. In situations of disagreement, consensus was achieved through discussion or by referring to a third reviewer. The whole process of selection adhered to the PRISMA 2020 flow diagram format to allow proper systematic documentation and transparency in including studies. Data Analysis and Grouping Systematically using a standardized data extraction form, data from the last set of included studies were extracted. Author, publication date, type of study, organism or population under study, PAH exposure information, method of assessing DNA methylation, target genes or genomic regions, and principal findings were the main information that was obtained. Following data collection, research was categorized into three broad categories: (1) Global DNA methylation changes, (2) Gene-specific methylation profiles, and (3) Epigenetic aging and disease susceptibility. Intercomparison between human and animal studies was performed to discern stable methylation patterns and related environmental health outcomes that follow PAH exposure. Enabling thematic categorization and easier identification of biological mechanisms connecting PAHs with risk of disease, this categorization ensured organization. Synthesis of Results Qualitative synthesis was conducted because of methodological, population, and exposure heterogeneity across the studies included in the review. Data between epidemiological and toxicological studies were compared to determine convergent evidence for PAH maternal exposure and DNA methylation effects. For instance, Li et al. (2018) and Campisi et al. (2023) showed that exposure to chronic PAH accelerates DNA methylation aging and changes genes involved in oxidative stress, while Wang et al. (2023) and Duca et al. (2018) established the same effects in well-controlled experimental models. These studies altogether indicated that PAHs induce gene-specific alterations in methylation, which have the potential to interfere with normal cell regulation and disease development. In summary, the synthesis points to uniform epigenetic "footprints" of PAHs that connect exposure with long-term health hazards such as cancer, cardiovascular disease, and metabolic disorders. RESULTS AND DISCUSSION The incomplete burning of organic materials produces the ubiquitous environmental contaminants known as polycyclic aromatic hydrocarbons, or PAHs. These substances are known to cause cancer and mutagenesis, but there is mounting evidence that they also have minor but important epigenetic impacts, especially through modifications in DNA methylation. A number of diseases, including cancer, metabolic disorders, and cardiovascular dysfunctions, have been linked to disruptions in DNA methylation, which is essential for controlling gene expression and preserving genomic integrity. Over the past ten years, there have been many studies describing how PAHs affect DNA methylation in humans, animals, and cell models. The studies showing the impact of these pollutants on the biological clock and disease susceptibility help understand the epigenetic changes. The major studies detailing PAH-induced changes in DNA methylation and their health impacts are compiled in Table 1. Table 1. Summary of Selected Studies on PAH Exposure, DNA Methylation, and Disease Susceptibility Author(s)/ Year Focus of the Study Key Findings / Results Author’s Recommendations 1 Chen et al. (2024) Examined DNA methylation changes in people exposed to multiple industrial pollutants. Identified pollutantspecific and cumulative exposure effects on DNA methylation patterns, indicating potential biomarkers of mixed industrial exposure. Recommend developing exposure biomarkers to monitor health risks among industrial workers and implementing stricter emission control measures. 2 Campisi et al. (2023) Investigated effects of high PAH exposure on biological aging indicators. Found that elevated PAH exposure was associated with Suggest conducting longitudinal studies to clarify causal Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [490] accelerated biological aging, reflected by changes in DNA methylation age and telomere shortening. relationships and promoting interventions that minimize PAH exposure in occupational environments. 3 Ruiz-Hernandez et al. (2015) Reviewed evidence linking environmental chemicals to DNA methylation in adults. Concluded that various pollutants (e.g., PAHs, metals) cause epigenetic alterations influencing chronic disease risk; emphasized the need for longitudinal studies. Recommend integrating epigenetic monitoring into public health policies and prioritizing long-term studies to establish exposure–effect pathways. 4 Li et al. (2018) Explored the link between PAH exposure and DNA methylation aging. Higher PAH exposure correlated with accelerated DNA methylation age, suggesting PAHs contribute to epigenetic aging and potential age-related diseases. Recommend further exploring age-related biomarkers as predictors of exposure effects and implementing stricter air quality standards. 5 Das & Ravi (2022) Discussed PAH-induced epigenetic toxicity and implications for human health risk assessment. Highlighted that PAHs can cause persistent DNA methylation and histone modification changes, which may serve as biomarkers for toxicity and disease risk. Suggest using epigenetic biomarkers in health risk assessments and encouraging reduction of PAH emissions through clean energy transitions. 6 Poursafa et al. (2022) Studied whether DNA methylation mediates the relationship between air pollution and metabolic syndrome. Found evidence supporting DNA methylation as a mediator between pollution exposure and metabolic alterations, linking environmental stressors to metabolic disorders. Propose policy interventions targeting pollution reduction and further research into epigenetic mechanisms linking air pollution to metabolic diseases. 7 Duca et al. (2018) Investigated PAH-induced DNA and RNA (hydroxy)methylation in rats. Observed nonmonotonic modulation of (hydroxy)methylation, suggesting complex dose-response effects of PAHs on epigenetic regulation. Recommend mechanistic studies to clarify dosedependent responses and improve toxicological models for PAH exposure. 8 Wang et al. (2023) Examined benzo(a)pyreneinduced dynamic DNA methylation changes in cancer cells. Found that benzo(a)pyrene alters methylation of oncogenes and tumor suppressor genes, Suggest using DNA methylation profiles as early indicators of cancer risk and enhancing regulations on PAH- Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [491] promoting carcinogenesis. related industrial processes. 9 Puvvula et al. (2024) Studied maternal exposure to nonpersistent chemicals and DNA methylation in placenta and cord blood. Maternal chemical biomarkers correlated with altered methylation in genes related to fetal growth and development. Recommend monitoring maternal PAH exposure during pregnancy and establishing guidelines to protect fetal health. 10 Montano et al. (2025) Reviewed occupational exposure to PAHs, health risks, and fertility effects. Highlighted that occupational PAH exposure leads to oxidative stress, DNA methylation disturbances, and reduced reproductive health outcomes. Propose implementing workplace safety standards, regular exposure assessments, and awareness programs for high-risk occupations. Table 1 shows that studies regarding the changes in DNA methylation attributed to exposure to PAHs shows that these pollutants exert toxicity primarily through epigenetic changes. Studies in both humans and animals illustrate the methylation changes within the genes responsible for the inflammation, the metabolism, and the oxidative stress, and cell proliferation. These changes are also related to the development of chronic diseases such as cancer, cardiovascular disease, and metabolic syndrome. Moreover, human cohort studies (e.g., Chen et al., 2024; Campisi et al., 2023; Li et al., 2018) suggest that DNA methylation can serve as a predictive biomarker for cumulative exposure and accelerated biological aging. These findings demonstrate how environmental pollutants like PAHs can "reprogram" gene expression without altering DNA sequences, emphasizing the long-term health implications of environmental exposures. Experimental works (e.g., Duca et al., 2018; Wang et al., 2023) further strengthen the mechanistic understanding by showing causative links between PAH-induced methylation and carcinogenic transformation. To summarize, the results indicate that the exposure of PAHs can be considered an even bigger concern in relation to toxicity, as it can trigger molecular mechanisms of epigenetic dysregulation. The evidence continues to grow of DNA methylation being a sensitive marker of exposure as well as a possible early marker for disease due to the environment, contributing greatly to the public health risk assessment and the formulation of policies. Environmental Exposure from Air, Water, Soil, and Food PAHs demonstrate moderate persistence in the environment and are prone to bioaccumulation. The concentrations of PAHs in aquatic organisms, such as fish and shellfish, are expected to be significantly higher than in the surrounding environment. Bioaccumulation has also been noted in terrestrial invertebrates. However, the activity of metabolic processes is adequate to prevent biomagnification. Given the ubiquitous nature of polycyclic aromatic hydrocarbons as environmental contaminants, pervasive across all environmental matrices, humans are exposed to these compounds through various pathways, including inhalation, dermal contact, and ingestion via air, water, soil, and food (Figure 2) Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [492] + Figure 2. Main sources of human exposure to PAHs, including food, air, water, and soil. On the left, the various sources of PAHs in the air are outlined in detail. The primary pathways for human exposure to PAHs are through the ingestion of contaminated food, the inhalation of ambient air, and the smoking of cigarettes or exposure to smoke from open fireplaces. Although there may also be exposure to PAHs through contaminated water and soil, these exposure routes can be considered of lesser importance than those mentioned above, as any contamination of these compartments, in the majority of cases, results in the contamination of food for human consumption, thus falling into the food category. The inhalation of PAHs occurs through various sources, including tobacco smoke, the combustion of fossil fuels and biomass, and high-temperature cooking. Among the myriad chemical constituents of cigarette smoke, PAHs represent a significant threat to human health. Tobacco is estimated to contain 100 ng or more of total PAHs per gram, and smokers inhale approximately 0.26 μg of benzo[a]pyrene per pack of 20 cigarettes. For non-smokers, the main means of exposure to PAHs is through consuming contaminated food. PAH contamination in food can come from both environmental sources and food processing methods. In unprocessed foods, PAHs mainly result from environmental pollution, such as particulate matter from the air settling on crops like wheat, fruits, and vegetables; absorption from contaminated soil by root vegetables like potatoes and carrots; and bioaccumulation in aquatic organisms such as fish, mollusks, and crustaceans from polluted waters. In processed foods, common sources of PAHs include high-temperature cooking techniques like grilling, frying, baking, and toasting, as well as certain manufacturing processes, particularly drying and smoking. PAHs in food can be categorized as “endogenous” PAHs, generated through the pyrolysis of carbohydrates, lipids, and proteins during high-temperature cooking processes, and “exogenous” PAHs, originating from fuel combustion during cooking or smoking. Food processing techniques such as drying and high-temperature cooking methods (e.g., grilling, roasting, frying) are significant sources of PAH contamination in food. Grilling, specifically, can generate PAHs through the incomplete combustion of lipids that fall onto the heat source. The literature indicates a strong correlation between the PAH concentrations in grilled meat, their fat content, and their Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [493] proximity to the heat source. In smoked fish and meat products, the PAH levels can reach up to 200 μg/kg, while grilled meat can contain approximately 130 μg/kg of PAHs. The baseline PAH levels in uncooked foods typically range from 0.01 to 1 μg/kg. Contemporary research demonstrates that, in grilled meat products, direct exposure to flames results in substantial PAH formation, with the benzo[a]pyrene concentrations reaching up to 200 µg/kg. Conversely, embers emit considerably smaller quantities (1–20 µg/kg) of benzo[a]pyrene. Exogenous PAHs, generated from fuel combustion, can contaminate food surfaces through the combustion gases and fumes. The fuel type and smoke generation conditions play a crucial role, particularly in smoking processes. Dietary intake, including the consumption of cereals, vegetables, fruits, meat, fish, oils, tea, and coffee, is the main way in which humans are exposed to PAHs. An analysis of 23 polycyclic aromatic hydrocarbons in various bread varieties revealed total PAH concentrations ranging from 2.61 μg/kg to 43.4 μg/kg, with variations observed between the crust and the crumb. While grilled and smoked meat and fish contribute to polycyclic aromatic hydrocarbon intake, cereals, fats, and oils represent the primary dietary sources of PAHs. Drying processes and combustion fumes are key factors in PAH contamination, particularly in seed oils and pomace oil production. The PAH concentrations are typically elevated in products cultivated in proximity to roadways and urban centers due to vehicular and industrial emissions. Trace quantities of PAHs such as phenanthrene, fluoranthene, and pyrene are ubiquitous in unprocessed fruits and vegetables, with lighter PAHs like naphthalene, acenaphthylene, and acenaphthene also detected in certain varieties. An investigation conducted in Saudi Arabia revealed elevated PAH concentrations in root vegetables such as potatoes (11 μg/kg) and carrots compared to turnips (9.26 μg/kg). Among fruits, the peel exhibited greater contamination than the flesh. Cabbage demonstrated the highest PAH levels among leafy vegetables (8.34 μg/kg). The benzo[a]anthracene concentrations were the highest in turnips (2.21 ± 1.75 μg/kg), while the benzo[e]pyrene levels were the highest in potatoes (2.90 ± 1.10 μg/kg). Elevated PAH concentrations in leafy vegetables, a significant dietary component for many African populations due to their recognized health benefits, present a substantial health risk to consumers. Various leafy vegetable species were sampled from farms situated along Nima Creek, Accra, Ghana. Varying concentrations of acenaphthene, acenaphthylene, benzo[a]anthracene, benzo[b]fluoranthene, and benzo[a]pyrene were detected, while naphthalene was ubiquitous across all vegetable samples. The mean phenanthrene concentrations in Chinese cabbage varied across different plant tissues, following the order of roots (0.744 ± 0.16 μg/kg) ≥ leaves (0.598 ± 1.21 μg/kg) ≥ stem (0.327 ± 1.01 μg/kg). Undeniably, both food processing methods (such as dehydration and smoking) and high-temperature cooking techniques (like grilling, roasting, and frying) lead to significant levels of PAHs. Additionally, some crops may either produce PAHs on their own or absorb them from environmental sources like water, air, or soil, contributing to human exposure to these contaminants. Occupational Exposure Occupational PAH exposure can arise from the inhalation of exhaust fumes by workers and those engaged in mining, metalworking, or petroleum refining. As early as 1775, occupational skin cancer was linked to soot exposure among London’s chimney sweeps. Soot contains elevated levels of PAHs, which were among the first substances identified as carcinogens. This finding was subsequently corroborated among workers within the paraffin industries of Scotland and Germany. Investigations of occupational PAH exposure have predominantly concentrated on industrial sectors such as coke oven production, asphalt/bitumen/road paving, metallurgy, electrode manufacturing, aluminum production and smelting, and oil refining. Secondary areas of focus include non-industrial sectors such as firefighting and waste incineration and, to a lesser degree, restaurant workers, police officers, drivers, air force personnel, groundskeepers, and naval personnel (Figure 3). Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [494] Figure 3. Occupational routes of PAH exposure are shown, arranged from the highest to lowest levels of exposure, from left to right. Several investigations have explored the potential correlations between airborne PAHs, typically measured using passive air samplers, and biomarkers of exposure. The most commonly employed urinary markers in these studies were 1-hydroxypyrene (1-OH-PYR) and 3-hydroxybenzo[a]pyrene (3-OH-BaP). For instance, within the United States population, a geometric mean 1-OH-PYR concentration of 79.8 ng/L was observed. Adult smokers exhibited urinary 1-OH-PYR levels threefold greater than those of non-smokers. Typically, elevated airborne concentrations correlate with increased urinary metabolite levels in exposed workers. A cross-industry occupational hygiene assessment, conducted to ascertain the exposure levels within United Kingdom industries, revealed an 8 h time-weighted average airborne PAH concentration range of 0.4–1912.6 µg/m3. A strong correlation was observed between the 1-OH-PYR levels and airborne benzo[a]pyrene concentrations (0.01–6.21 µg/m3). It is important to acknowledge that PAH exposure involves a complex mixture of compounds; thus, a single metabolite cannot be universally employed to assess exposure to all PAHs. A correlation between the atmospheric and urinary PAH metabolite concentrations is not consistently observed, suggesting that, in certain occupational settings, exposure routes other than inhalation, such as dermal absorption, may be significant. Coke oven workers are recognized as a high-risk occupational group for PAH exposure. Across various coking production sectors, the total airborne PAH concentrations have been measured to be between 12 and 47 µg/m3, with benzo[a]pyrene concentrations ranging from 0.05 to 1.05 µg/m3. This substantial exposure elevates the risk of PAH-related health complications, including carcinogenesis and respiratory ailments, among coke oven workers, emphasizing the critical need for stringent occupational safety protocols in these environments. While the measured PAH concentrations in coke oven settings fall slightly below the recommended exposure limit of 0.1 mg/m3 for a 10 h workday or 40 h workweek, as advised by the National Institute for Occupational Safety and Health (NIOSH), these findings nevertheless raise substantial concerns. This is particularly relevant in the absence of adequate personal protective equipment (PPE). Even concentrations below the regulatory thresholds can present substantial health risks if workers lack sufficient protection, as chronic PAH exposure, even at low levels, can result in long-term adverse health outcomes, including carcinogenesis, respiratory illnesses, and other toxic effects. The utilization of appropriate PPE is essential in mitigating these risks and safeguarding worker health. Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [501] Contemporary research has increasingly emphasized the exposome, encompassing the totality of environmental exposures and individual experiences throughout the lifespan. Nayak et al. investigated the relationship between the seminal PAH exposome and sperm function in idiopathic male infertility by analyzing spermatozoa proteins and gene expression. They concluded that seminal PAH concentrations, along with oxidative protein modifications and the expression of the aryl hydrocarbon receptor and heat shock protein 90-beta (HSP90-B), could serve as biomarkers in differentiating between idiopathic infertile and fertile men. Elevated PAH concentrations were observed in the urine of the selected infertile groups, suggesting a strong correlation between PAH exposure and male infertility. Several mechanisms are thought to contribute to the detrimental effects of PAHs on fertility. One such mechanism is DNA methylation, which has been explored in recent studies analyzing a cohort of policemen and their exposure to air pollution. Epigenetic alterations can modify gene expression profiles without altering the underlying DNA sequence. PAH-induced epigenetic changes in sperm may impact fertility and contribute to reproductive health problems. One potential mechanism is the action of PAH metabolites as endocrine-disrupting compounds (EDCs), a class of chemicals that can interfere with both hypothalamic– pituitary–gonadal axis hormones and testicular hormones. Strong support for this perspective comes from the European Association of Urology, which has attributed idiopathic male factor infertility to endocrine disruption resulting from reactive oxygen species, genetic anomalies, and environmental contamination. These compounds have been demonstrated to interact with hormone receptors and disrupt the synthesis and signaling pathways of reproductive hormones, including testosterone and follicle-stimulating hormone. Certainly, several studies have indicated that these compounds can emulate endogenous hormones; for instance, their metabolites may exhibit estrogenic activity or disrupt thyroid function, thereby affecting the hypothalamic– pituitary–thyroid axis and hypothalamic–pituitary–gonadal axis. However, the precise mechanism by which PAHs exert their toxic effects on male fertility remains elusive. Some researchers have proposed that PAHs may bind to and activate the aryl hydrocarbon receptor, leading to the increased metabolism of PAHs into DNA-reactive products. Studies have shown that human sperm expresses aryl hydrocarbon receptor and aryl hydrocarbon receptor nuclear translocator mRNA, suggesting a potential impact on sperm function. Reactive metabolites generated by cytochrome P450 enzymes induce the production of reactive oxygen species (ROS), which can cause DNA oxidation or the formation of PAH-DNA adducts. These adducts are recognized as indicators of sperm genotoxicity and male factor infertility. Elevated levels of ROS can suppress steroidogenesis and induce mitochondrial membrane degeneration in spermatozoa. An alternative mechanism involves the formation of PAH epoxide metabolites via a cytochrome P450-dependent monooxygenase system. The overexpression of this system can augment the generation of reactive oxygen species, leading to DNA damage. Certainly, oxidative stress is associated with diminished sperm function and is a contributing factor to male infertility. Impacts of PAHs on Female Fertility Beyond the well-established effects of environmental PAH exposure on male reproductive health, accumulating evidence suggests detrimental effects on the female reproductive system as well. Bolden et al. highlighted that PAHs may cause damage to egg cell DNA and disrupt ovarian function, which could contribute to conditions like polycystic ovary syndrome, miscarriage, and preterm births. As previously mentioned, PAHs can exert estrogenic or antiestrogenic effects, acting as endocrine disruptors of reproductive function. Their impact on female fertility has been recognized since 1998, when Zenzes et al. reported PAH-induced DNA adducts in the granulosa cells of women undergoing in vitro fertilization who were exposed to cigarette smoke. Subsequently, they also observed a higher prevalence of these adducts in the embryos of couples who smoked compared to those of non-smoking couples. This suggests that PAH-induced DNA damage may be transmitted to the progeny. The mechanisms by which PAHs affect female fertility have become a subject of intense research. These mechanisms appear to be similar to those affecting male fertility. PAH exposure can induce oxidative stress in the reproductive tissues, including the ovaries and testes. PAHs generate reactive oxygen species during their metabolism, potentially overwhelming the endogenous antioxidant defenses and causing cellular damage. Oxidative stress can impair gamete quality and function, contributing to infertility. PAH metabolites are genotoxic and can form DNA adducts, inducing mutations. DNA damage in gametes can lead to genetic abnormalities in offspring and increase the risks of infertility and adverse pregnancy outcomes. Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [502] PAH-induced epigenetic changes in the reproductive tissues may affect gene regulation and cellular functions that are essential for fertility and reproductive success. PAH exposure can also trigger inflammation and immune responses in the reproductive system, further compromising fertility. It has been demonstrated that chemical insults can deplete the primordial follicle pool, adversely affecting fertility. Conversely, xenobiotic exposures that induce damage to primary, secondary, and antral follicles may result in transient infertility and anovulation. When PAH exposure affects the entire follicle pool, either temporary infertility or premature ovarian insufficiency may ensue. Benzo[a]pyrene is metabolized via a specific pathway in the ovaries, generating metabolites implicated in the pathogenesis of infertility and cancer. Numerous investigations employing in vivo animal models have suggested that PAHs exert deleterious effects on ovarian follicles, oocytes, and cumulus–oocyte complexes via mechanisms analogous to those described for spermatozoa. PAHs present in the follicular fluid of women exposed to cigarette smoke undergoing in vitro fertilization negatively affect ovarian germ cells. Numerous in vivo and in vitro studies have explored the association between PAH exposure and ovarian germ cell apoptosis. Exposure to benzo[a]pyrene disrupts mouse oocyte meiotic progression by interfering with normal spindle assembly, chromosome alignment, and kinetochore–microtubule attachment, resulting in the production of aneuploid eggs. Consequently, benzo[a]pyrene exposure diminishes female fertility by impairing oocyte maturation. Furthermore, environmental PAH exposure is correlated with alterations in endocrine markers of ovarian function in women, exhibiting PAH-specific patterns. Another compelling aspect of fertility is the influence of PAHs on infertility in couples. Numerous studies have investigated populations of couples undergoing fertility treatment and IVF cycles. For instance, a small-scale, monocentric cohort study by Netter et al. compared PAH exposure between couples with positive versus negative human chorionic gonadotropin results 14 days after embryo transfer. Their findings revealed that the urinary 1hydroxypyrene (1-OH-PYR) levels were significantly lower in women with positive HCG tests compared to those with negative results. The urinary 1-OH-PYR levels in women correlated with embryo fragmentation in the highest-quality embryos, suggesting a relationship between PAH exposure and reduced embryo quality. Moreover, the urinary concentrations of hydroxylated PAHs, particularly 2-hydroxyphenanthrene plus 3hydroxyphenanthrene (2 + 3 PHE), were positively associated with early pregnancy loss in women undergoing in vitro fertilization–embryo transfer (IVF-ET). Table 3. Reproductive Health Impacts and Symptoms Associated with Polycyclic Aromatic Hydrocarbons (PAHs) Source Human Health Impacts Symptoms PAH exposure (female reproductive system) Damage to egg cell DNA, disruption of ovarian function, conditions like polycystic ovary syndrome, miscarriage, preterm birth, endocrine disruption, reduced fertility. Infertility, miscarriage, hormonal imbalances, polycystic ovary syndrome, disrupted menstrual cycles. PAH-induced DNA adducts in females DNA damage in oocytes, embryo quality impairment, genetic abnormalities, possible transgenerational effects. Reduced embryo quality, potential for genetic abnormalities in offspring, impaired oocyte maturation. Oxidative stress in female reproductive tissues Oxidative stress in ovaries and other reproductive tissues, impaired gamete quality, infertility. Reduced egg quality, difficulty conceiving, impaired reproductive function. Benzo[a]pyrene exposure (female fertility) Impaired oocyte maturation, disrupted meiotic progression, chromosome alignment issues, possible infertility. Impaired egg maturation, reduced fertility, aneuploidy in eggs, fertility problems. Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [503] PAH exposure (male reproductive system) Decreased sperm quality (DNA damage, dysfunction), infertility, impaired semen parameters, oxidative stress, DNA methylation, endocrine disruption. Reduced sperm count, motility, concentration, and morphology; erectile dysfunction. PAH exposure and sperm DNA damage PAH-induced sperm DNA damage, decreased sperm quality, possible infertility. Reduced sperm motility, concentration, and morphology; increased DNA damage in sperm. Urinary PAH metabolites in male infertility Elevated urinary PAH metabolites associated with idiopathic male infertility, disrupted sperm function, oxidative protein modifications. Impaired sperm function, lower sperm count and motility. PAH-induced epigenetic alterations (male) Epigenetic modifications in sperm DNA, impaired fertility, potential for transgenerational effects. Altered gene expression in sperm, reduced fertility potential, genetic instability. PAH exposure (endocrine disruption in males) Endocrine disruption via interference with reproductive hormones, including testosterone and follicle-stimulating hormone, potentially affecting sperm function. Disrupted hormone levels, reduced testosterone, impaired sperm production. Reactive oxygen species and PAH exposure (male) Increased ROS production in sperm leading to DNA oxidation, sperm genotoxicity, infertility, mitochondrial degeneration, and diminished sperm function. Reduced sperm motility, compromised DNA integrity, mitochondrial damage. PAH exposure in occupational settings (male) Long-term PAH exposure in occupations linked to increased male infertility risk, decreased sperm parameters, potential genetic mutations. Reduced sperm concentration, morphology, motility, and genetic integrity; possible infertility. The findings of the aforementioned studies demonstrate a substantial inverse correlation between PAH metabolites and sperm parameters (concentration, volume, motility, morphology), as well as DNA integrity, suggesting a link between PAH exposure and male factor infertility. Based on expert opinion, further investigation is warranted to elucidate the precise relationship between PAH exposure and adverse reproductive outcomes in humans, particularly in occupational settings. Many studies have measured the PAH concentrations in biological fluids (e.g., semen), without accounting for the potential contributions of other pollutants to the observed detrimental effects. Maternal Exposure Puvvula et al. (2024) examined the relationship between maternal exposure to non-persistent environmental chemicals during pregnancy and alterations in DNA methylation patterns in placental tissues and cord blood mononuclear cells (CBMCs). The study was conducted in the United States as part of a hospital-based cohort involving 75 pregnant women recruited from the University of Cincinnati Medical Center between 2014 and 2017. Eligible participants were healthy women aged 18–45 years with singleton pregnancies and without major medical complications. Urinary samples collected at delivery were analyzed for 37 biomarkers of environmental exposure, including phenols, phthalates, phthalate replacements, and polycyclic aromatic hydrocarbons (PAHs), of which 29 were retained for epigenetic analyses. Placental tissues from both maternal and fetal sides, as well as CBMCs, were obtained at delivery for DNA methylation profiling using the Illumina HumanMethylation450K BeadChip array. Differential methylation of CpG sites Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [504] Multivariable linear regression models were used to examine associations between log-transformed urinary biomarker concentrations and methylation M-values, adjusting for maternal age, race, education, tobacco use, prepregnancy BMI, infant sex, and estimated cell-type proportions. False discovery rate (FDR) correction was applied to control for multiple testing. Among the 22 continuous biomarkers analyzed, seven exhibited statistically significant associations with differentially methylated CpG sites (q < 0.05), predominantly observed in the fetal side of the placenta. Figure 5. Summary of CpG-specific associations (q-value < 0.05) with gestational chemical biomarkers. Horizontal bars represent the total number of CpGs associated with chemical biomarkers by methylation sample source. MP-maternal side placenta, FP-fetal side placenta. Vertical bars represent the number of CpG associations that overlap across and are exclusive to a chemical biomarker. Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [505] Figure 6. Association between PAH biomarkers concentrations and CpG methylation intensities. This figure covers 1-hydroxynaphthalene and 2-hydroxyfluorene. Methylation intensities from fetal-side placenta (FP) and maternal-side placenta (MP). The x-axis represents the beta coefficient values, and the y-axis represents raw p-values on the -log10 scale. The CpG ID, chromosome position, and UCSC Reference Gene names were labeled. CpG-specific associations with q-values < 0.05 were color-coded in red (hypomethylation) and blue (hypermethylation) Several PAH metabolites—including 1-hydroxynaphthalene, 2-hydroxynaphthalene, 2-hydroxyfluorene, 2,3hydroxyphenanthrene, 4-hydroxyphenanthrene, and 1-hydroxypyrene—were associated with widespread Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [506] methylation differences. For instance, 2-hydroxyfluorene was linked to 46 CpG sites in the fetal placenta and 10 sites in the maternal placenta, while 1-hydroxypyrene was associated with 31 CpG sites in the fetal placenta, 23 of which overlapped with those identified for 2-hydroxyfluorene. These CpGs were located near genes such as ZNF354C, CCDC63, and MFSD2A, suggesting possible impacts on transcriptional regulation and placental transport function. Enrichment of Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways Significant associations were also found for several phthalate metabolites, particularly mono-3-carboxypropyl phthalate (MCPP), which was linked to 130 CpGs in the maternal placenta and 69 in the fetal placenta. These sites were located near genes related to DNA repair (LIG4) and immune response (CSF3). Table 4. Identified Pathways Associated with Chemical Biomarkers in Placental Samples Chemical Biomarker Sample Pathway ID Description p-value 1-Hydroxynaphthalene FP hsa00061 Fatty acid biosynthesis 2.86e-03 1-Hydroxynaphthalene FP hsa00071 Fatty acid degradation 6.25e-03 1-Hydroxynaphthalene FP hsa04216 Ferroptosis 6.72e-03 1-Hydroxynaphthalene FP hsa01212 Fatty acid metabolism 9.38e-03 1-Hydroxynaphthalene MP hsa03450 Non-homologous end-joining 4.96e-03 1-Hydroxynaphthalene MP hsa05168 Herpes simplex virus-1 infection 7.93e-03 Mono-3-carboxypropyl phthalate MP hsa03450 Non-homologous end-joining 2.22e-03 Mono-3-carboxypropyl phthalate MP hsa04613 Neutrophil extracellular trap formation 9.00e-03 hsa – homo sapiens; FP – fetal-side placenta; MP – maternal-side placenta The Kyoto Encyclopedia of Genes and Genomes pathway enrichment analysis in this study identified potential involvement of several biological pathways including lipid metabolism, ferroptosis, viral infection response, and DNA repair. However, these associations did not remain statistically significant after correction for false discovery rate (FDR). Importantly, significant correlations between maternal exposure biomarkers and placental cell-type proportions were observed: PAH biomarkers were negatively associated with B-cell and nucleated red blood cell proportions, while phthalate metabolites were positively linked to CD4+ T-cells and trophoblast cells, suggesting immunological and developmental impacts. This study provides strong evidence that maternal urinary concentrations of PAHs, phthalates, and phenols are significantly associated with widespread epigenome-wide changes in placental DNA methylation, especially on the fetal side of the placenta. These results support the hypothesis that the placenta is a sensitive target for maternal chemical exposure, translating environmental signals into epigenetic modifications that may influence fetal development. Despite limitations including modest sample size, single-timepoint exposure measures at delivery, and limited coverage of CpG sites, these findings contribute important mechanistic insights into how maternal environmental exposures alter placental epigenetic profiles and may have lasting effects on offspring health outcomes (Hou et al., 2024). Associations between maternal chemical biomarkers and estimated cell composition This study provides strong evidence that maternal urinary concentrations of PAHs, phthalates, and phenols are significantly associated with epigenome-wide changes in placental DNA methylation, particularly on the fetal side of the placenta. These findings support the hypothesis that the placenta acts as a sensitive target and mediator of maternal chemical exposure, translating environmental signals into epigenetic modifications that may influence fetal development. The authors noted several limitations, including a modest sample size, single-timepoint exposure measurement at delivery, and limited CpG coverage of the 450K array. Nevertheless, their findings Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [507] contribute valuable mechanistic insights into how maternal environmental exposures can alter placental epigenetic profiles and potentially affect offspring health outcomes. ACKNOWLEDGEMENT We would like to express our deepest and sincerest gratitude to everyone who has played a part in the successful completion of our systematic review entitled “Epigenetic Footprints of Polycyclic Aromatic Hydrocarbons: A Systematic Review on DNA Methylation and Disease Susceptibility.” This systematic review became possible through the collective support, guidance, and encouragement of many individuals who inspired and helped us throughout this journey. Our heartfelt appreciation goes to our professor, Ms. Gecelene Estorico, for her unwavering patience, insightful guidance, and constant encouragement. Her invaluable knowledge, thoughtful suggestions, and constructive feedback have not only strengthened the quality of our work but also deepened our understanding of environmental science. Her support has motivated us to go beyond our limits and to approach our research with integrity, curiosity, and critical thinking. We also extend our gratitude to the authors and researchers whose scholarly works served as the cornerstone of our study. Their dedication to advancing knowledge in epigenetics, toxicology, and environmental health provided the foundation upon which this review was built. Lastly, we offer our profound and heartfelt thanks to Almighty God, the source of our strength, wisdom, and perseverance. Through every challenge and uncertainty, His divine guidance has given us clarity, patience, and hope. This accomplishment stands as a reflection of His boundless grace and unwavering presence in every step of our journey. CONCLUSION Conclusion The systematic review highlights the findings on the maternal exposure on the polycyclic aromatic hydrocarbons (PAHs) on the epigenetic changes, especially involving the DNA methylation, which is crucial in determining the likelihood of developing diseases. The PAH metabolites such as 1-hydroxynaphthalene, 2-hydroxyfluorene, and 1-hydroxypyrene found in cohort and birth studies were linked with changes in the methylation of the geneassociated CpG sites for the oxidative stress response, lipid metabolism, cellular transport, and even DNA repair. The changes in gene-specific methylation, in particular, ZNF354C, CCDC63, and MFSD2A, suggest that maternal exposure to PAHs could alter normal placental functioning, and fetal development might also be affected. The findings suggest that the placenta functions as an epigenetic intermediary, carrying the mother's environmental influences to the fetus, for instance, during the crucial stages of molecular programming. This can result in long-term predisposition that may translate into chronic ailments in the offspring including metabolic and respiratory abnormalities, cardiovascular diseases, and neurodevelopmental issues. This underscores the vital role of DNA methylation as the key mechanism through which an interplay of the maternal environment and the mother's methylome affects the health of the offspring. Overall, this review finds that the negative consequences of maternal PAH exposure include not just immediate toxicity but also long-lasting epigenetic reprogramming that alters gene expression and increases the risk of disease in subsequent generations. Such findings highlight the necessity of considering maternal environmental exposures as potential immediate health risks and, through epigenetic inheritance, focal determinants of future disease risk. Recommendations Future research should prioritize longitudinal and mechanistic studies to clarify the cause and effect relationship between PAHs, DNA methylation, and downstream outcomes. To enhance the comparison and harmonization of findings, research teams should use standardized methodologies to assess exposure and epigenetic changes. Accepting the challenge of identifying and characterizing methylation ACEs and gene-specific methylation signatures should be prioritized, as they have great potential to be used as early detection and risk assessment Volume-09 Issue 10, October-2025 ISSN: 2456-9348 Impact Factor: 8.232 International Journal of Engineering Technology Research & Management (IJETRM) https://ijetrm.com/ IJETRM (http://ijetrm.com/) [508] tools. In the same context, public health practitioners and lawmakers should respond to the potential of epigenetic factors by ensuring they are included in the frameworks of active surveillance and regulation of environmental and occupational exposures. Education about minimizing PAH exposure through cleaner energy alternatives, improved food preparation and cooking methods, and greater control of air pollution should be prioritized in primary prevention and community action plans. 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