Toxic Growth: How Urbanization Threatens Planetary and Public Health

By Ian Ségal

May 20, 2025

(Illustration by Segalian Advisors, 2025)

Introduction

Urbanization is a complex and dynamic process that reshapes natural systems and human societies, often producing far-reaching consequences for environmental health. Within the broader framework of planetary health, which highlights the deep interdependence between ecological well-being and human survival, urban expansion acts as both a driver of progress and a source of environmental strain. As cities grow, they demand more resources, generate concentrated pollution, disrupt water systems, and create dense living conditions that can accelerate the spread of infectious diseases.

These outcomes are not isolated events but part of a network of interrelated effects, where deteriorating air quality can impair immune function, polluted runoff compromises drinking water, and inadequate infrastructure amplifies public health vulnerabilities. Applying a systems-thinking approach enables us to trace these feedback loops, identify root causes, and develop sustainable policies that address environmental health as a collective whole rather than a series of disconnected problems. In this context, exploring the interconnections between air pollution, water quality, and infectious diseases offers a powerful lens for understanding how urbanization shapes the health of both people and the planet.

Issues with Increased Air Pollution

One of the most visible and immediate consequences of urbanization is a rise in air pollution. As urban centers expand, so do the activities that contribute to air pollution, particularly due to traffic emissions and increased industrial output. The rapid population influx into cities leads to increased vehicular traffic, a primary source of urban air pollution. Research indicates that urbanization is directly correlated with increased levels of airborne particulate matter (PM) and nitrogen dioxide (NO2), both of which have well-documented adverse effects on human health (Gong et al., 2012). Moreover, studies highlight that structural changes in urban environments, including increased industrialization, further worsen these pollution levels (Gong et al., 2012).

(Illustration by Segalian Advisors, 2025)

For example, the interrelationship between urbanization and public health has been underlined by reports linking urban air quality deterioration with increased rates of respiratory diseases, thereby necessitating immediate policy measures to curb emissions (Gong et al., 2012). Additionally, urbanization can intensify heat island effects, which compound the effects of air pollution. As warmer temperatures exacerbate the formation of ground-level ozone, they further impact respiratory health (Connolly et al., 2020).

Issues with Reduced Water Quality

A second major challenge linked to urban expansion is water quality degradation. Urbanization has a profound impact on water quality, primarily through increased runoff and pollution from residential, commercial, and industrial sources. The intensity of urban development leads to the degradation of natural waterways, as highlighted in studies demonstrating that urban streams suffer significant pollution due to untreated sewage and stormwater runoff (Rühling Tagliari et al., 2024; Askarizadeh et al., 2015). An example of this can be seen in urban streams, which often exhibit altered hydrology, aggravating problems related to nutrient loading, sedimentation, and increased turbidity, all of which critically influence aquatic ecosystems and human water supplies (Rühling Tagliari et al., 2024).

(Illustration by Segalian Advisors, 2025)

Also, the construction and expansion of urban areas reduce the permeability of the ground, leading to greater surface overflow during precipitation events. This situation is known as urban stream syndrome, which describes the cascade of ecological and hydrological changes that occur following urban development (Askarizadeh et al., 2015). As a result, water quality degrades, contributing to the proliferation of waterborne diseases and thus representing a significant public health concern (Rühling Tagliari et al., 2024; Askarizadeh et al., 2015).

Rise in Infectious Diseases

In addition to its environmental impacts, urbanization has significant implications for the spread of infectious diseases. The relationship between urbanization and infectious diseases is multifaceted and has been a focal point of contemporary public health research. Urban settings often create environments that facilitate the spread of infectious diseases due to high population density and close human contact (Blake et al., 2024). For instance, studies have shown that urbanization can increase risks of zoonotic disease transmission as wildlife habitats are encroached upon, and interfaces between wildlife, livestock, and human populations emerge (Hassell et al., 2017).

(Illustration by Segalian Advisors, 2025)

Moreover, the COVID-19 pandemic has highlighted how densely populated urban areas are particularly susceptible to rapid disease spread, underscoring the vulnerabilities inherent in urban living arrangements (Connolly et al., 2020). Conversely, it has been noted that urban centers with better healthcare infrastructure might perform more effectively in managing certain infectious diseases compared to rural counterparts, where resources are limited (Wood et al., 2017). This duality suggests that while urbanization presents novel challenges for infectious disease control, it can also offer opportunities for enhanced public health interventions.

Concluding Thoughts

Urbanization has significant implications for planetary health, contributing to increased air pollution, degraded water quality, and heightened vulnerability to infectious diseases. These environmental health issues do not occur in isolation—poor air quality can compromise respiratory health and immune response, polluted water sources can become breeding grounds for pathogens, and dense urban populations create ideal conditions for disease transmission. This illustrates how the interplay between these factors creates a compounded public health burden. Importantly, these burdens are not evenly distributed. Marginalized communities—often along racial, ethnic, or socioeconomic lines—frequently experience the greatest exposure to environmental hazards while having the least access to healthcare and adaptive infrastructure.

Addressing these challenges requires a systems-thinking approach that goes beyond treating individual symptoms. Instead, it promotes solutions that consider the complex relationships between urban infrastructure, ecological resilience, and human well-being. Through integrated planning, robust environmental policy, and equitable public health strategies, cities can evolve to sustain both people and the planet.

References

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Blake, E., Stringham, E., & Sloan-Aagard, C. (2024). Concurrent disease burden from multiple infectious diseases and the influence of social determinants in the contiguous United States. Plos One, 19(9), e0293431. https://doi.org/10.1371/journal.pone.0293431

Connolly, C., Ali, S., & Keil, R. (2020). On the relationships between COVID-19 and extended urbanization. Dialogues in Human Geography, 10(2), 213-216. https://doi.org/10.1177/2043820620934209

Connolly, C., Keil, R., & Ali, S. (2020). Extended urbanisation and the spatialities of infectious disease: Demographic change, infrastructure and governance. Urban Studies, 58(2), 245-263. https://doi.org/10.1177/0042098020910873

Gong, P., Liang, S., Carlton, E. J., Jiang, Q., Wu, J., Wang, L., & Remais, J. V. (2012). Urbanisation and health in China. The Lancet, 379(9818), 843–852. https://doi.org/10.1016/s0140-6736(11)61878-3

Hassell, J., Begon, M., Ward, M., & Fèvre, E. (2017). Urbanization and disease emergence: Dynamics at the wildlife–livestock–human interface. Trends in Ecology & Evolution, 32(1), 55-67. https://doi.org/10.1016/j.tree.2016.09.012

Rühling Tagliari, L., Roberto Gehling, G., & Wohlmuth da Silva, S. (2024). Water quality index applied to an urban stream located in  Porto Alegre, Rio Grande do Sul, Brazil. Revista Brasileira de Engenharia e Sustentabilidade, 11, 1–25. https://doi.org/10.15210/rbes.v11i.26226

Wood, C., McInturff, A., Young, H., Kim, D., & Lafferty, K. (2017). Human infectious disease burdens decrease with urbanization but not with biodiversity. Philosophical Transactions of the Royal Society B Biological Sciences, 372(1722), 20160122. https://doi.org/10.1098/rstb.2016.0122