Ants can act as biological indicators of pollution from traffic in the city: the magnetic particles that accumulate on the surface of their bodies increase in places crossed by a greater number of vehicles.
This is what emerges from a study by the University of Parma, published in the journal Environmental Pollution, which examined specimens of the Crematogaster scutellaris species collected in 30 sites in the city with different traffic levels and in four control areas without vehicular circulation.
The ‘magnetism’ of ants
In the model developed by the researchers, every thousand additional daily vehicles were associated with an increase in about 41 percent of the magnetic susceptibility measured on ants. The same relationship did not emerge in the soil samples analyzed, suggesting that these insects may offer a complementary tool to the control units to identify urban areas in which to deepen environmental monitoring. The research, entitled ‘Ants as bioindicators of urban traffic pollution’, used an arboreal ant as a sentinel organism, Crematogaster scutellaris.
The researchers compared the particles accumulated on the insects and those present in the ground with the official data on traffic flows recorded by the Municipality of Parma in the different areas of the city. The objective was to verify whether the ants could record local differences in the deposition of magnetic particulates associated with vehicular circulation. To characterize the collected material, the group combined magnetic susceptibility measurements and scanning electron microscopy. The first technique allows you to detect the magnetic response of the material present on the samples; the second allows you to observe the particles and analyze their characteristics.
The results showed a strong association between traffic intensity and the magnetic susceptibility of the ants. In the statistical model of the study, each increase of a thousand vehicles per day corresponded to a multiplication of the value measured on insects by 1.41, equivalent to an increase of approximately 41 percent. The particles were concentrated especially on the thorax of ants. They were rich in iron oxides and also contained zinc, copper and titanium, with sizes and shapes compatible with those of traffic-derived particulates. The comparison with the soil samples highlighted a difference: in the soil the same relationship between magnetic susceptibility and vehicular flows was not observed.
The importance of nest fidelity
According to the authors, this result indicates that the surface of the ants can provide information on the local deposition of particles that does not emerge as clearly from soil analysis. “The most interesting fact is that the ants do not simply record the presence of particles: thanks to their fidelity to the nest, their foraging activity and direct contact with the environment, they return a local and integrated footprint over time of the exhibition”, explains Donato A. Grasso, scientific coordinator of the study and researcher of the Department of Chemical, Life and Environmental Sustainability Sciences of the University of Parma.
The possibility of using ants as environmental sentinels also derives from their habits. The individuals of a colony move around the area surrounding the nest while searching for food and repeatedly come into contact with environmental surfaces. The particles that settle on their body can then offer an indication of local conditions in frequented places. The study looked at magnetic particulate matter accumulated on insects: it did not directly measure people’s exposure or demonstrate health effects on ants or humans. The work involved researchers with biological, ethological, ecological, mineralogical and physical expertise. In the Department of Chemical, Life and Environmental Sustainability Sciences, Daniele Giannetti, Antonio Verolino, Enrico Schifani, now a postdoctoral researcher at the Universitat Pompeu Fabra in Barcelona, Luciana Mantovani and Grasso collaborated. Francesco Cugini, Daniele Pontiroli and Massimo Solzi, from the Department of Mathematical, Physical and Computer Sciences of the University of Parma, contributed to the magnetic characterization.
The interaction between biology and environment
“It is a very concrete example of how biology, ecology, mineralogy and materials physics can converge to build new tools for reading the environment“, observes Grasso. “The ants do not replace the control units, but they can represent a very sensitive biological matrix useful for identifying, with a much finer spatial resolution, critical areas in which to concentrate instrumental measurements and interventions.” The application proposed by the researchers involves a two-phase analysis system. The first would consist of a relatively rapid and economical screening based on the magnetic susceptibility of the ants; in the sites identified as worthy of further study, a characterization of the particles would follow. A protocol of this type could contribute to the creation of maps more detailed analyzes of the deposition of magnetic particulates and guide targeted air quality monitoring campaigns. Before large-scale use, the method will need to be verified in different seasons, cities and environmental conditions.