The researchers measured ambient concentrations of particulate matter across three size classes: PM1.0, particles smaller than one micrometer; PM2.5, the fine fraction under 2.5 micrometers that is widely associated with cardiovascular and respiratory disease; and PM10, which includes coarser dust and industrial debris up to ten micrometers. Across both seasons, overall average concentrations reached 77.14 micrograms per cubic meter for PM1.0, 105.40 micrograms per cubic meter for PM2.5, and 277.64 micrograms per cubic meter for PM10. Every one of those figures sits far above the air quality guideline levels recommended by the World Health Organization, underscoring the severity of the exposure environment in a city where glass manufacturing furnaces operate continuously and emit a cocktail of fine particles and metal-laden aerosols.

Seasonality emerged as a decisive factor. When the team compared size-fractionated averages between the two seasons, they found that winter carried roughly 1.2 times the particulate load of summer. This pattern is familiar across the Indo-Gangetic Plain, where cooler temperatures, temperature inversions, reduced wind speeds, lower mixing heights, and increased biomass burning for heating and cooking conspire to trap pollutants near the ground. In an industrial city like Firozabad, those meteorological conditions stack on top of constant emissions from glass kilns, compounding the exposure burden precisely when people also tend to spend more time indoors and in close proximity to combustion sources.

But ambient concentration is only half the story. What ultimately matters for health is the dose that actually deposits in the respiratory system, and that depends on particle size, breathing pattern, and the anatomy of the airways. The study modeled deposition through both oral and nasal breathing routes, the two principal pathways by which inhaled particles enter the body. The nose acts as an efficient filter for larger particles, while mouth breathing bypasses some of that filtration and delivers a higher fraction of inhaled material deeper into the lungs. By modeling both scenarios, the researchers could compare how the route of entry alters the regional distribution of deposited material across the head airways, the tracheobronchial region, and the pulmonary — or alveolar — region where gas exchange occurs.

The results point squarely at the most vulnerable members of the population. Infants and young children were found to be highly affected by the smallest particles, with deposition fractions of PM2.5 reaching 78.28 percent in winter and 79.14 percent in summer in the pulmonary region, and PM1.0 deposits of 78.09 percent and 78.23 percent across the same seasons and region. In other words, nearly eight out of every ten fine or ultrafine particles inhaled by a child were predicted to settle in the deepest, most delicate portions of the lungs. This vulnerability arises because children breathe faster per unit of body weight, have narrower airways, and possess respiratory systems that are still developing, making them biologically less equipped to clear deposited particles and more susceptible to the inflammation and oxidative stress those particles trigger.

Notably, the total regional deposition fraction was nearly identical through nasal and oral breathing, at approximately 16.67 to 16.68 percent in both winter and summer. That convergence suggests that in this exposure environment, the choice of breathing route does little to change the overall burden, even though the regional distribution within the respiratory tract may differ. It also implies that the sheer magnitude and size distribution of the particulate load — dominated by fine particles capable of penetrating beyond the nose’s filtering capacity — overwhelms the protective differences between the two routes. For public health planning, the practical consequence is that reducing ambient concentrations, rather than modifying behavior related to breathing, remains the most effective lever for lowering deposited dose.

The study went beyond particle counts to evaluate the chemical dimension of the risk, assessing the carcinogenic and non-carcinogenic health hazards posed by metals bound to the particulate matter. Chromium emerged as the metal of greatest carcinogenic concern. Through ingestion and inhalation exposure pathways respectively, chromium showed carcinogenic health risk during winter in adults at values of 2.90E-03 and 6.37E-03, and in children at 2.32E-02 and 9.29E-04, while in summer the corresponding values were 1.88E-03 and 4.12E-03 for adults and 1.50E-02 and 6.01E-04 for children. Carcinogenic risk values in this framework represent the incremental probability of developing cancer over a lifetime of exposure; values above the conventional threshold of one in a million (1.0E-06) are considered significant, and several of the reported figures exceed that benchmark by orders of magnitude. The children’s ingestion pathway figure of 1.50E-02 in summer and 2.32E-02 in winter is particularly alarming, pointing to exposure routes such as hand-to-mouth dust transfer that are especially relevant for young children.

Alongside the cancer risk findings, the analysis revealed that nickel and cobalt presented the highest non-carcinogenic risk to residents. Non-carcinogenic risk is typically expressed as a hazard quotient comparing estimated intake with a reference dose below which no adverse effect is expected; values exceeding unity indicate potential for harm to organs and systems such as the lungs, kidneys, liver, or skin with chronic exposure. Nickel and cobalt are common associates of high-temperature industrial processes, including the glass melting operations that define Firozabad’s economy, and their presence in the respirable fraction means they are delivered directly to lung tissue with every breath taken in polluted conditions.

The broader context of these findings is sobering. Air pollution has been classified as a Group 1 human carcinogen by the International Agency for Research on Cancer, and global burden of disease studies consistently rank it among the leading risk factors for premature death worldwide, with South Asia bearing a disproportionate share of the toll. Studies across the Indo-Gangetic Plain have documented persistently elevated PM2.5 and PM10 concentrations driven by a mix of industrial emissions, vehicular exhaust, road and construction dust, and seasonal crop residue burning. What this new study adds is the explicit link between that external environment and the internal dose: a quantitative bridge from ambient micrograms per cubic meter to percentages of particles deposited in specific lung regions of specific age groups, season by season and breathing route by breathing route.

For Firozabad’s residents, and for populations of similar industrial cities across the region, the message is clear. Winter brings a measurably heavier particulate load, children absorb a substantially larger fraction of it into their pulmonary regions than adults, and the metals riding on those particles carry carcinogenic and non-carcinogenic risks that exceed accepted safety thresholds through both inhalation and ingestion. The authors argue that exact evaluation of particulate dose and respiratory deposition is essential for designing appropriate risk control strategies, and their results suggest those strategies must prioritize the finest particle fractions, target the industrial sources that generate them, and focus protective measures on infants and children, whose developing lungs bear the deepest burden of the city’s polluted air. As industrialization intensifies across South Asia, studies of this kind provide the evidentiary foundation for the regulatory action and public health interventions that the region’s youngest and most vulnerable residents urgently need.

Subject of Research: Seasonal deposition of size-segregated particulate matter in human lungs and associated metal health risks in an Indian industrial city.

Article Title: Seasonal variation of particulate matter deposition in human lungs through different exposure pathways in an industrial city

Article References: Rajouriya, K., & Taneja, A. (2026). Seasonal variation of particulate matter deposition in human lungs through different exposure pathways in an industrial city. Environmental Monitoring and Assessment, 198(10), Article 1068. https://doi.org/10.1007/s10661-026-15885-y

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15885-y

Keywords: particulate matter, PM2.5, lung deposition, air pollution, Firozabad, glass industry, health risk assessment, heavy metals, chromium carcinogenic risk, children's health, seasonal variation, respiratory dose