The Levels of Heavy Metal Pollution are Going Down at the Largest Metropolis of the Southern Hemisphere

The Levels of Heavy Metal Pollution are Going Down at the Largest Metropolis of the Southern Hemisphere

Brazilian researchers showed that the environmental pollution in Sao Paulo has gone down in the last 30 years by analyzing the rings and barks of the Tipuana tree.

Environmental Pollution is one of the massive challenges that we face in this modern era. Following the disastrous impacts, it can have, global efforts are needed to control the situation before it is too late. Very large cities, like the capitals of state or country, are affected the most in this regard due to the frequency of the developmental projects in these regions. For instance, Sao Paulo, the biggest metropolis of Brazil, is considered one of the most polluted cities in the world. However, a recent study published in the journal ‘Environmental Pollution’ showed that the levels of heavy metal pollution have gone down in that part of the world.

Researchers from the University of Sao Paulo joined forces with the scientists of the University of Campinas to figure out that the Tipuana tree, a native species of Bolivia, is incredibly useful for measuring the environmental pollution levels in the long run. They analyzed the chemical composition of growth rings and tree barks of the 3 most common tree species in the city (Tipuana, Privet, and Sibipiruna). The Sao Paulo Research Foundation provided great help to this research by offering a Postdoctoral Research Scholarship in addition to a regular research grant.

The age of the tree can be judged by its number of growth rings because each one of them represents a year. The rings closer to the center are narrower in comparison to the farther ones. The most recent year is represented by a ring which is farthest from the center while the ring for the first year of the tree’s life lies closest to the center. The chemical composition of these rings clearly indicates the levels of heavy metals absorbed by the tree each year. Consequently, the variation in pollution can easily be determined through these results on a scale of decades. Giuliano Maselli Locosselli, the Lead Author of the study who is a Postdoctoral Researcher at the Bioscience Institute of the University of Sao Paulo, mentioned that by saying,

If a tree is 50 years old, for example, it will tell the story of pollution in the city during that period.

The roots of the Tipuana tree transport these heavy metals to the growth rings after absorbing them from the ground. They make use of the sap and the xylem cells for this purpose. Similarly, the bark of the Tipuana trees store those chemicals from the atmosphere that are deposited on the external side of the trunk. The analysis of these samples extracted from the bark of trees, planted in different parts of the city, helps the researchers to observe the variations on a scale of years. Locosselli referred to that in the following words:

It’s easier to obtain samples of bark than annual growth rings, and the chemical analysis of bark is less costly, so we can analyze samples from many trees and cover a large area. The result is a map of pollution by heavy metals and other chemical elements throughout the city.

Growth rings from two 35-year-old Tipuana trees were extracted from the Medical School of the University of Sao Paulo which lies in the western parts of the city. Pressler Increment Borer was used for this purpose as it can cut a cylindrical section of wood tissue from a living tree, without doing too much damage to the plant. These 15-mm rings were then sent to the Chemistry Institute of the University of Campinas where Marco Aurelio Zezzi Arruda scanned them with a laser to generate software-processed images. The researching team selected the necessary cells and examined them in-detail to measure the levels of heavy metals absorbed by the trees in each year.

They found a considerable reduction in the levels of pollution caused by Copper, Cadmium, Nickel, and Lead in the last 30 years. Similarly, a moderate decrease was observed in the levels of Zinc and Sodium. Marcos Buckeridge, Co-author of the study, said,

The falling levels of lead reflected the gradual elimination of this chemical element from the composition of Brazilian gasoline. The downtrend in cadmium, copper and nickel pollution probably reflects enhanced vehicle efficiency and deindustrialization in São Paulo.

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