A new study, conducted in a rapidly developing city in China, discovered that urbanization increases the proportion of disease-causing bacteria in the air and the overall amount of airborne microbes. Airborne microbe risk to human health increases with urbanization, especially during the summer.
Released earlier this month, the study focus on the microbiome of urban air. Bacteria can easily become airborne by being lofted into the air from the environment, shedding from humans, as well as other sources. The researchers looked at multiple urban, suburban, and rural sites in and near Xiamen, China. Xiamen is a port city located directly west of Taiwan across the Taiwan straight. It's known for its mild subtropical climate and relatively low air pollution. Summers are hot and humid while winters are mild and dry. The scientists also examined seasonal differences in the airborne bacteria.
About 2% of the bacteria sampled were pathogenic. During the summer it increased to 3% and during spring it fell to 1%. Although this seems low, humans breathe in a large amount of bacteria with every breath, though we have various defenses to protect from infection. During the summer, regions sampled near hospitals saw even higher percentages of pathogenic bacteria. The researchers examined all pathogenic bacteria. In this study, just over a third of disease-causing airborne microbes were infectious to humans. The other two-thirds infect plants, animals, and other organisms.
Why does urbanization increase both the number of airborne bacteria as well as the proportion that cause disease? Increasing urbanization raises the concentration of gas pollutants which can provide nutrients for microbes, supporting their survival and growth. Wastewater treatment plants are a large source of pathogenic bacteria. They concentrate other sources of bacteria, like feces, industrial and domestic sewage. Pathogenic bacteria can continue to grow in bioactivated sludge or effluents after entering the treatment plants. The bacteria from these sources can enter ambient air in urbanized areas.
Another reason why urban and suburban sites have more pathogenic bacteria compared to rural zones are the differences in biological sources of bacteria. In cities, humans incubate and shed bacteria that contribute to the urban air microbiome. At the same time, bacterial contributions from seawater and vegetation are reduced in urbanized areas compared to rural zones.
The diversity, or number and evenness of the bacterial species, of the samples was different between rural and urban sites during the summer. This pattern was not found during spring. Diversity of airborne bacteria increases with more sources of bacteria. During the summer, strong winds can bring in bacteria from other regions, such as the ocean or more agricultural areas. The humidity and high temperatures encourage increased growth of bacteria on various surfaces, which eventually increases the number of airborne microbes.
The diversity of the bacterial microbiome in 40 Chinese cities is different - each has their own signature. Environmental factors, seasonal variations, and human activities structure the airborne microbiome of the cities.
This article is culled from daily press coverage from around the world. It is posted on the Urban Gateway by way of keeping all users informed about matters of interest. The opinion expressed in this article is that of the author and in no way reflects the opinion of UN-Habitat.