Loss of urban biodiversity is a threat to human health

Loss of microbial biodiversity in degraded soils, which is particularly prevalent in cities, promotes the spread of bacterial pathogens and antibiotic resistance, says an international study. Restoring green spaces, by contrast, creates a biological barrier to their spread

by Matteo Cavallito

 

The loss of biodiversity in urban areas linked to decreasing green spaces and increasing pollution is reducing people’s exposure to the benefits provided by soil microbes. Within this framework, city residents experience an increased risk of developing allergies and other diseases in the absence of interventions designed to reverse the phenomenon. A group of scientists from China, Europe and Flinders University in Adelaide, Australia, says in a paper published in the journal Njp Urban Sustainability.

“With 70% of the human population expected to live in cities by 2050, we argue that we need to maintain contact with healthy soil both indoors and outdoors to maintain and improve immune fitness, help to suppress pathogens and benefit the human microbiome,” says leading author Professor Xin Sun, who leads the Urban Soil Ecology Group at the Institute of Urban Environment at the Chinese Academy of Sciences.

The link between soil biodiversity and health

According to the authors, a relevant link would exist between biological and microbial diversity on the one hand and people’s well-being on the other. “The potential for improving human health by enhancing urban soil biodiversity is an important yet little understood field of fundamental and applied research,” She says. But the real problem, the researchers notice, is that the current scenario appears very problematic.

Indeed, declares Martin Breed, professor at Flinders University and co-author of the study, “Cities are seeing the collapse of the natural environment, destablised food webs and rapid changes to soil biodiversity, which in turn risks creating unhealthy urban environments.”

In short, says Craig Liddicoat, a researcher at Flinders key factors such as soil sealing, compaction and vegetation removal, are impacting soil “which traditionally have been one of Earth’s largest reservoirs of biological diversity.”

Urban ecosystems are incubators of diseases

According to the study, urban ecosystems are incubators of emerging diseases. That’s a consequence of their ability to accelerate the persistence and spread of zoonotic pathogens (i.e., which can be transmitted directly or indirectly from animals to humans, ed.) through the soil especially in tropical regions. These harmful microorganisms are most prevalent in disturbed and degraded soil ecosystems. Which, in turn. are especially prevalent in cities.

“Therefore, a long list of human bacterial and fungal pathogens may be present in urban soils,” the research states. “This list includes biological agents causing serious human diseases such as tetanus, anthrax, botulism, gastrointestinal, wound, skin, and respiratory tract diseases.”

Moreover, “Some human pathogens have also gained resistance against treatments, with the most notorious example being antibiotic resistant bacteria that are increasing through inappropriate use of antibiotics,” the study continues. Such bacteria are prevalent in urban environments, both outdoors and indoors. “Importantly, multidrug resistant human pathogenic bacteria that are now a common issue for hospitals mostly originate in soils.”

The solution? Restore and expand green spaces

The good news, the researchers explain, is that increasing the complexity of soil biota can effectively reduce human-transmitted pathogens. “The suppression of pathogens by increased soil biodiversity has largely been shown in agricultural ecosystems for plant pathogens,” the study says. “For example, soils in natural systems with higher biodiversity can reduce the incidence of soil-borne plant diseases by inducing plant defense, producing antibiotics, competing with pathogens, and regulating plant immune systems.”

In summary: while loss of microbial diversity exacerbates the invasiveness of bacterial pathogens and resistance to antibiotics, the maintenance of a wide variety of microorganisms in the soil can act as a biological barrier to the spread of harmful agents.

Hence the authors’ call for restoring and expanding green spaces to reduce the risk of disease. Areas for action, after all, are many and include large urban parks, private yards, potted houseplants and roadsides. “We need to revisit strategies to rebuild the quality and exposure to soils via restoration,” Martin Breed adds. “And work on more creative ways of greening and rewilding our cities to improve not only the environment, but also our own health.”