Air pollution stands out as a paramount environmental challenge, posing significant threats to global well-being. An alarming 90% of the global population is exposed to contaminated air, resulting in approximately seven million deaths annually (Dávila-Román et al., 2021; Organization, W. H, 2018; Tarín-Carrasco et al., 2021; Zacarias and Grubert, 2021). This menace extends beyond human health, adversely impacting ecosystems and the ozone layer (de Vries, 2021; Liao et al., 2021; Rupakheti et al., 2021). The origins of air pollutants are diverse, stemming from unregulated urbanization, industrial emissions, fossil fuel consumption, and tobacco smoke (Aksoy et al., 2021). Indoor air pollution, an overlooked yet critical facet, proves to be even more hazardous, with data indicating pollution levels up to 100 times higher than outdoor air (Caselli et al., 2010; Mason et al., 2000; Wood et al., 2006). Elevated concentrations of indoor air pollutants pose severe risks to human and plant health (Brilli et al., 2018; Cetin et al., 2019). Notably, cigarette smoke in indoor environments emerges as a significant contributor, introducing a plethora of toxic compounds (Zai et al., 2012). The toll on human life is staggering, with over eight million global deaths attributed to smoke exposure, encompassing both active smoking and passive exposure (non-smokers) (Organization, W. H and others, 2015). Understanding the nature and cause of indoor pollutants, as well as distinguish them from outdoor pollutants, is essential for health risk assessment (Obore et al., 2020). It is also vital for setting regulatory strategy for indoor air quality (IAQ) and developing effective mitigation strategies to reduce human contact to air pollution, irrespective of its origin (Blount et al., 2021; Isinkaralar et al., 2024; Rajagopalan and Goodman, 2021).

Tobacco products, including cigarettes and water pipes, are major contributors to indoor air pollution. Cigarette smoke comprises two types: mainstream smoke (inhaled by the smoker) and side-stream smoke (emitted from the burning end). Environmental tobacco smoke is composed of approximately 85% side-stream smoke, which contains higher levels of toxic gases. Likewise, mainstream smoke consists of 92% gaseous elements and 8% tar. Side-stream smoke contains higher levels of toxic gases compared to mainstream smoke. Cigarette smoke consists of two phases: a tar (particulate) phase and a gas phase, which together deliver an estimated load of over 10¹⁷ and 10¹⁵ free radicals per puff, respectively, as determined through electron spin resonance (ESR) spectroscopy (Pryor and Stone, 1993). The gas phase includes carcinogens such as acrolein, acrylonitrile, hydrocyanic acid, acetaldehyde, nitrogen oxides, and carbon monoxide, and remains active for a shorter duration than the tar phase. Cigarette smoke is highly damaging to human health, causing antigenic, cytotoxic, mutagenic, and carcinogenic effects. Given that individuals spend more than 80% of their time indoors, vulnerable populations—such as children, the elderly, and plants used for air purification—are at heightened risk from indoor air pollutant (Berglund et al., 1992).

Indoor plants are negatively affected by cigarette smoke, absorbing various toxic elements and contaminants from the air (Forster et al., 2018; Rumchev et al., 2017). Despite prohibitions on cigarette use in many countries, smoking still occurs in enclosed spaces (Fix, 2019). Indoor plants serve as effective biomonitors, absorbing pollutants and helping to assess IAQ. Several biomonitoring studies have highlighted the capacity of different plant species to capture and reflect air quality indices, including those impacted by cigarette smoke (Kumakli et al., 2017; Vimercati et al., 2016). However, prolonged exposure to smoke can result in morphological and physiological damage, such as chlorosis, necrosis, leaf curling, and reduced growth in ornamental species (Benson et al., 2019; Gushit et al., 2022; Viana, 2011). The presence of toxic metals from tobacco smoke necessitates monitoring IAQ at its source. Indoor plants face stresses from IAQ, water availability and concentration of smoke, impacting their ability to absorb toxic metals. Research indicates that ornamental species growing in smoky areas may experience leaf degradation due to this absorption. PM also attaches to various organs of plants such as hairy leaves or bark (Hatami-Manesh et al., 2021) which produce ill effect in plant development. Because leaves are the organs with air entry and exit through their stomata, and they interact with air the most. Leaves, being the primary interface for gas exchange, play a critical role in pollutant uptake. The extent of toxic metal absorption is influenced by the physical and chemical properties of the metals, plant species, organ morphology, surface area, surface texture, environmental conditions, and exposure duration (Shahid et al., 2019). PM also accumulates on rough surfaces such as hairy leaves or bark, further contributing to physiological stress (Hatami-Manesh et al., 2021). However, the accumulation of toxins may vary on the basis of plant organ and species of plants (Gorena et al., 2020). The differences among tobacco products and plant species can provide insights into air pollution effects and help identify potential bio-monitor species. Their exposure to smoke can lead to leaf degradation and stress. Numerous plant studies have also been conducted on bio-monitoring of toxins from cigarette smoke (Kumakli et al., 2017; Vimercati et al., 2016), but the direct physiological effects of cigarette smoke exposure on indoor plants remain underexplored.

The present investigation aims to assess the effects of cigarette smoke on plants physiology and morphology of the indoor plant species Epipremnum aureum (money plant). This species is chosen for its widespread presence and heightened sensitivity, making it a frequent subject in experimental studies. The central hypothesis is that continuous and prolonged exposure to cigarette smoke leads to measurable and dose-dependent physiological and morphological stress in E. aureum. These stress responses introduce adverse effects like reduced photosynthetic efficiency, loss of chlorophyll content, leaf deformation, and signs of oxidative damage.

Chlorophyll a fluorescence (ChlF) is employed as a widely accepted and non-invasive technique to detect plant stress conditions, often integrated with other physiological and chemical variables (Miranda et al., 2020; Percival et al., 2006). This provides a quantitative measure of oxygenic photosynthesis (Ashraf et al., 2019). Exposure to CS disrupts photosynthesis through chemical interactions with proteins, leading to an escalation in reactive oxygen species generation (Dobaradaran et al., 2021; Yadav, 2010). These findings will provide a more precise understanding of how smoke pollutants affect plants growth and development.

The growth of E. aureum was significantly affected by the CS, which caused modulation of the plant’s photosynthetic process. To investigate this phenomenon, the current study explored the impact of CSC on various parameters on E. aureum including morphological parameters, chlorophyll fluorescence, specific energy fluxes, phenomenological energy fluxes, and performance indexes.

The detrimental effects of CS on the growth and physiological health of indoor plants are well-documented, with the extent of impact varying by plant species. In this study, exposure to low concentrations of CS (2 CSC) led to a minor reduction in the surface area of E. aureum plants. However, at higher concentrations (≥6 CSC), a significant decrease in surface area was observed. Previous study, by Prasad et al. (2015), have similarly reported that lower concentrations of cigarette butts (CBs) produce less pronounced effects, while higher concentrations (greater than 20 CBs) inhibit plant growth. Additionally, increased mortality rates were observed over time with higher CSC treatments, accompanied by a reduction in leaf number. This phenomenon is attributed to excessive exposure to CSC, which negatively affects plant survival. Moreover, gases from cigarette smoke, such as sulfur dioxide (SO₂), nitrogen dioxide (NO₂), carbon radicals, ammonia, and volatile organic compounds, can be absorbed through the stomata of the leaves. These gases may damage the leaves and alter photosynthetic capacity, particularly at high concentrations (Permana et al., 2023).

Decreases in chlorophyll content can lead to a reduction in antenna size (Kirst et al., 2024; Martini et al., 2024). Strategic modulation of chlorophyll content or antenna size—such as reducing excess pigment to prevent light oversaturation under high light conditions—has been shown in some cases to enhance photosynthetic efficiency by minimizing energy loss and photo-inhibition. However, excessive reduction may impair light capture and thus negatively affect photosynthetic performance. At the canopy level, reduced leaf chlorophyll content can increase leaf transmittance, improve light distribution within the canopy, and thereby enhance canopy photosynthesis, as suggested by modeling studies (Song et al., 2021). Conversely, there are instances where chlorophyll-deficient mutants exhibit decreased photosynthetic rates. For example, the mutation of OsClpP6 impairs the photosynthetic apparatus and chloroplast development (Dong et al., 2013). Similarly, the loss of the transcription factor OsPIL1 leads to a decrease in chlorophyll content, accompanied by a reduction in plant surface area (Mao et al., 2023). In our study, cigarette smoke exposure significantly reduced chlorophyll content in E. aureum, which was associated with a decline in photosynthetic efficiency and visible morphological stress, indicating the detrimental impact of smoke-induced chlorophyll loss on overall plant health.

The minimal fluorescence intensity values are a key indicator of the extent of irreversible damage to PSII, particularly to the light-harvesting complex II (LHCII). Such damage can hinder electron transfer on the reduced side of PSII (Goltsev et al., 2016; Kalaji et al., 2014). The disruption of the electron transport chain can be attributed to the degradation of the LHCII oligomer. Additionally, the presence of heavy metal ions in CS can enhance the dissipation of excitation energy as heat, a process known as non-photochemical quenching (Janeczko et al., 2005). A reduction in minimal fluorescence under high concentrations of cigarette smoke stress may indicate reduced PSII efficiency, likely due to conformational changes in the D1 protein induced by CS stress. These changes can alter the properties of PSII electron acceptors (Kalaji et al., 2014). Moreover, the presence of particulate matter in CS can limit the formation of PSI, PSII, and LHC complexes in E. aureum. Permana et al. (2023) conducted an experiment using CS exposure exclusively on Calathea makoyana, Their study demonstrated that prolonged exposure to CS under enclosed conditions resulted in visible chlorosis, reduced leaf turgor, and significant decreases in chlorophyll content, suggesting that CS-induced oxidative stress impairs photosynthetic efficiency and overall plant health. The oxygen-evolving complex within the PSII complex is essential for catalyzing redox reactions and splitting water during photosynthesis (Ifuku et al., 2010). This process produces dioxygen and hydrogen ions, which are necessary for ATP phosphorylation (Paul et al., 2022). Given the disruption of the photosynthetic apparatus by CS, our findings suggest that cigarette smoke stress may increase the physiological demand for water in E. aureum, as the plant attempts to compensate for impaired energy production by enhancing water-dependent processes such as ATP synthesis and organic compound biosynthesis. Water is a crucial component in plant physiological processes, especially photosynthesis (Treesubsuntorn et al., 2021).

The F₀/F_M ratio is an important parameter in the JIP test that indicates the efficiency of primary light energy conversion in the PSII reaction center (Baker et al., 2004; Kalaji et al., 2012; Schansker et al., 2005). It is commonly used as a stress indicator in various photosynthetic studies. This ratio depends on the fluorescence levels of F₀ and F_M, and any decrease in F_M can lead to a reduction in the F₀/F_M ratio with increasing levels of CSC. PCA reveals a positive correlation between dissipation per reaction center (DT₀/RC) and the F₀/F_M ratio. This indicates that as photochemical efficiency declines under CS stress, plants increasingly rely on non-photochemical energy dissipation pathways to protect the remaining functional PSII units. Such an increase in energy dissipation, reflected by higher DI₀/RC, has also been reported under various abiotic stresses, including heat, salinity, and drought, as a photoprotective mechanism (Kalaji et al., 2016). Therefore, the observed increase in both DI₀/RC and F₀/F_M under elevated CS concentrations suggests that CS imposes photoinhibitory pressure on PSII, and the plant attempts to mitigate this through increased energy dissipation. However, the observed increase in F_M values at early stages of 4–6 CSC treatments may appear contradictory. This anomaly could be due to transient photoprotective adjustments or measurement artifacts. The analysis of fluorescence transients, commonly known as the JIP test, in photosynthetic organisms exposed to abiotic stress, reveals a significant decrease in the φP₀ value. This reduction in φP₀ is due to a decline in the photochemical efficiency of PSII as a result of CS-induced stress. Under light conditions, the observed decrease in the maximum quantum yield of PSII (φP₀) indicates that CS stress disrupts the redox reaction following Q_A and delays electron transport between Q_A- and Q_B (Schansker et al., 2005). However, φP₀ alone provides only a partial understanding of PSII function. To more accurately assess the condition of the PSII acceptor side, additional parameters such as φE₀ (quantum yield of electron transport beyond Q_A ^-) and φD₀ were also considered. In our study, φE₀ showed significant reductions at higher CS concentrations and prolonged exposure times, supporting the notion that CS stress impairs the electron transport between Q_A ^- and Q_B. Conversely, φD₀ increased, suggesting enhanced energy dissipation mechanisms as a photoprotective response to CS stress. These combined changes indicate that CS negatively affects PSII function by disrupting the redox reactions at the acceptor side and enhancing energy dissipation to mitigate photodamage, as also supported by previous findings (Mykhaylenko and Zolotareva, 2017).

These fluorescence declines particularly in PI_ABS and φP₀, are consistent with photoinhibition mechanisms that limit PSII efficiency under oxidative stress. Reactive oxygen species generated by CS exposure likely disrupt photosynthetic proteins and membranes, thereby reducing the plant’s energy conversion capacity. Integrating these observations with oxidative stress markers would provide further clarity on the damage pathways. The ABS/RC ratio, which is determined by the total number of photons absorbed by chlorophyll molecules across all active reaction centers (RC) divided by the total number of active reaction centers, reflects the proportion of active versus inactive RCs. An increase in the number of active RCs leads to a higher ABS/RC ratio. Conversely, the TR₀/RC ratio measures the maximum rate at which excitons are captured by RC with a decrease in this ratio indicating a reduction in the population of the primary electron acceptor Q_A. An increased DI₀/RC ratio suggests a diminished amount of Q_A remaining in its reduced state. The analysis of specific energy flux reveals that various sites within PSII are sensitive to environmental stressors (Gautam et al., 2014; Zushi et al., 2012). The present study shows that with increasing concentrations of CS, the efficiency of electron trapping and transport in PSII declines, as active reaction RC are converted into inactive ones, thereby reducing the overall number of functional RCs. This decline in active RCs directly contributes to diminished photochemical efficiency and impaired electron transport. This decline is evident from the reductions in TR₀/CSm and ET₀/CSm values (Strasserf and Srivastava, 1995; Tsimilli-Michael, 2020; Zushi and Matsuzoe, 2017). A decrease in the ET₀/RC ratio indicates a reduced capacity for electron transport, as the inactive reaction centers are less capable of re-oxidizing the reduced Q_A (Rapacz et al., 2015). The DI₀/RC ratio, which represents the total dissipation of untrapped excitation energy per active RC, is influenced by the ratio of active to inactive RCs. Dissipation can occur through various pathways, including heat, fluorescence, and energy transfer to other systems. Despite variations in the active/inactive RC ratios, the DI₀/RC ratio remains relatively stable due to the effective utilization of energy by the active RCs (Grieco et al., 2015; Heber et al., 2011). Our results indicate that at higher CS concentrations (6, 8, and 10) during days 9, 12, and 15, the DI₀/RC ratio increases significantly. This suggests that under severe stress, the decline in active RCs surpasses the compensatory mechanisms, resulting in elevated energy dissipation per RC.

The phenomenological fluxes per cross-section—ABS/CSm, TR₀/CSm, ET₀/CSm, and DI₀/CSm—offer insights into the behavior of the entire PSII population rather than individual RCs. Under CS stress, ABS/CSm and TR₀/CSm declined, implying impaired light absorption and trapping capacity across the PSII antenna system. The reduction in ET₀/CSm further supports the view that CS impairs the linear electron transport chain, compromising the energy transduction processes essential for ATP and NADPH production (Kalaji et al., 2014; Stirbet et al., 2018). In contrast, DI₀/CSm increased with CS exposure, indicating a shift toward energy dissipation as heat or fluorescence, a typical response to protect the remaining functional PSII units from excess excitation pressure (Yusuf et al., 2010).

The performance index of a plant is a sensitive indicator of stress effects on its physiological components. This index is calculated using parameters based on energy absorption (PI_ABS) and cross-section (PI_CS), with PI_CS being dependent on phenomenological energy flux (Baker et al., 2004; Srivastava and Strasser, 1999). The performance index integrates multiple factors including the density of reaction centers, trapping efficiency, and electron transport efficiency, analogous to the Goldman equation (Goldman, 1943). In our study, exposure to CS significantly reduced the PI_ABS and PI_CS values in E. aureum. The decline in PI_ABS is linked to decreased activity of the RC, which in turn diminishes the overall efficiency of these centers (Kalaji et al., 2014, 2017; Kumar et al., 2020). The efficiency of electron trapping during the light reactions is crucial for plant productivity, as it directly impacts the plant’s ability to generate energy for growth and development (Sharma et al., 2023; Zhang et al., 2018). Through statistical analyses, including PCA and correlation matrices, we identified several JIP test parameters—such as ABS/CSm, TR₀/CSm, ET₀/CSm, φP₀, PI_ABS, and PI_CS—that exhibited a dose-dependent response to CS stress. Additionally, probit analysis of the LD₅₀ values revealed that CS is highly toxic to E. aureum. LD₅₀ of approximately 6.49, indicating that moderate levels of cigarette smoke can cause lethal stress in 50% of E. aureum plants. Early effects begin at lower concentrations (LD₁₀ ≈ 3.08), suggesting high sensitivity to smoke exposure. The steep rise in mortality beyond LD₅₀ highlights a dose-dependent toxicity pattern. These findings emphasize the harmful impact of cigarette smoke on indoor plants even at sub-lethal levels.

In conclusion, this study reveals the detrimental effects of CS on Epipremnum aureum, a commonly used indoor plant, highlighting the broader implications for indoor air quality and plant health. Our findings indicate that exposure to CS induces significant morphological alterations, leaf damage, and reduced overall vigor. These physical changes are accompanied by a reduction in chlorophyll content, measured using the Arnon (1949) method, and a decrease in photosynthetic efficiency, as indicated by changes in chlorophyll fluorescence parameters analyzed using Biolyzer software. These are important indicators of the plant’s overall health and vitality. The research shows a clear dose-response relationship, with higher concentrations of CS causing more severe damage, ultimately leading to plant mortality. This underscores the severe impact of CS, not only on plant life but also on the effectiveness of indoor plants in air purification. The results emphasize the necessity for improved indoor air quality management, particularly in environments where cigarette smoking is prevalent. By documenting these adverse effects, this study highlights the importance of using indoor plants as bio-indicators for air pollution and advocates for policies and practices aimed at reducing indoor pollutant levels. The evidence presented highlights the urgent need for a more integrated approach to managing indoor air quality, emphasizing its impact on both plant health and human well-being. Although research on plant–smoke interactions remains limited, our study contributes valuable insights to this emerging field. The observed effects of CS on indoor vegetation underline the importance of implementing stricter air quality regulations in enclosed environments where smoking occurs. To build on these findings, future research should incorporate molecular, physiological, and biochemical approaches to deepen our understanding of how airborne pollutants affect plant systems.