Juulia Manninen’s doctoral dissertation examined how urbanization and human activity shape bacterial communities in the environment. Previous studies have found that these microbial communities are linked to the risk of immune-mediated diseases in humans. In addition, the study investigated how pollutants typical of urban environments can alter the bacterial flora of children’s skin and intestines.
The study supports the so-called biodiversity hypothesis, which suggests that reduced exposure to the environment’s diverse microbiome due to human activity may increase the risk of immune-mediated diseases in urbanized societies.
Playground materials affect bacterial communities
The study found that the rubber mats commonly used in playgrounds and daycare centers support a poorer bacterial community than natural stone and rock surfaces. Rugged and dry natural surfaces were found to have a richer and more diverse bacterial flora than artificial materials resembling them.
“The choice of materials in children’s everyday environments, such as playgrounds and daycare center yards, can have a significant impact on microbial exposure,” notes doctoral researcher Juulia Manninen.
Green space management practices influence biodiversity
The study also found that the management of green spaces affects the local bacterial community. Less actively managed green spaces—such as lawns that are mowed less frequently—maintain a more diverse bacterial community, and this is already evident in the entrance areas of parks, where a large number of people pass through.
Based on the results, so-called “managed neglect” may offer a cost-effective way to increase bacterial diversity that is beneficial to health in urban environments.
Pollutants linked to children’s microbiome
The study also examined polycyclic aromatic hydrocarbons (PAHs), which are common harmful pollutants in urban environments and are known to be hazardous to health.
The results showed that PAHs accumulated in the homes of children living in the city were linked to the children’s skin and gut microbiota. Although the sample size was small, the results suggest that even relatively low concentrations of pollutants can affect children’s microbiota.
Toward healthier cities
The findings provide concrete evidence of how urban structural and functional solutions affect the environment and the human microbiome. The findings are particularly relevant for children living in cities, as early-life microbial exposure and the development of the microbiome play a key role in the development of the immune system.
“The findings can be utilized as practical tools in urban planning and environmental development. The use of more natural materials, reduced maintenance of green spaces, and the reduction of pollution can increase microbial exposure and support a healthy and diverse human microbiome,” Manninen summarizes.