Researchers map the distribution of chemical elements essential for the supply of drinking water
Rare earths are chemical elements that gained great importance during the technological revolution of recent decades, with their introduction in new materials to produce essential components of various items such as cell phones, televisions or solar panels. These elements occur naturally in rocks, soils and waters, in variable quantities, but almost always in the order of parts per million (rocks and soils) and per trillion (waters). Due to their increasing use, rare earth elements have also been added to the environment as a result of anthropogenic (human) activities. In his doctoral thesis, geologist Bruno Cesar Mortatti studied the distribution of the group of rare earths in the sub-basins of the Atibaia and Jaguari rivers, supervised by professor Jacinta Enzweiler, at the Institute of Geosciences (IG).
According to Bruno Mortatti, the Atibaia and Jaguari sub-basins are in the larger context of the Piracicaba river basin and are essential for supplying drinking water to part of the São Paulo population. “The rivers that feed these sub-basins are dammed and form the main reservoirs of the Cantareira system, which sends approximately 33 cubic meters of water per second to the São Paulo Metropolitan Region – data indicates that 94% of this volume comes from rivers that are object of our study. Due to their importance for public supply, we wanted to investigate how rare earth elements are distributed in the main types of rocks in the area and in the water of the rivers of the two sub-basins.”
The thesis author adds that when rocks alter and soils form, most of the original rare earth content is retained in the rocks themselves. In rivers, these elements are found in suspended material (often from erosion) and only a small fraction is actually dissolved. “In a previous study guided by Professor Jacinta, carried out in the most downstream portion of the Atibaia River, including its tributary Anhumas stream, the presence of gadolinium anomalies (one of the rare earths) due to human insertion into the environment was discovered. Precisely to understand the downstream signatures, we needed to study the upstream region, where they came from. This included the Atibainha and Cachoeira rivers, which form the Atibaia, as well as the other rivers and reservoirs that are part of the Cantareira system.”
Emerging Contaminants
According to Jacinta Enzweiler, rare earth elements are so named because, when they were discovered, their isolation and identification were not simple and it was also thought that they were not very abundant. However, they are widely disseminated and the amount of the rare earth most present in the Earth's crust, cerium, is approximately the same as copper, the element with which we are most familiar. “Under natural conditions, the transfer of rare earths from rocks to water is small because their solubility is very low. On the other hand, these elements may present slightly different behaviors in natural waters, as these often have different compositions (dissolved salts and acidity). But, in 1996, a first scientific article published in Germany showed the presence of gadolinium anomalies in the water of several rivers in that country, explained by the use of this element as an agent to enhance magnetic resonance images.”
The IG professor states that gadolinium, in a conventional solution, is extremely toxic. To avoid toxicity and maintain the function of enhancing images without interfering with human metabolism, gadolinium chelates are used, substances in which the same molecule forms several chemical bonds with the element, as if it were at the center of a cage. “Applied to patients in this way, gadolinium is excreted in the urine. It turns out that in sewage and conventional treatments, gadolinium chelates remain in the liquid medium and, therefore, are found in river waters. After the first article, which is more than 20 years old, gadolinium anomalies were observed in lakes, groundwater, treated water and numerous rivers – as rivers flow into the oceans, anomalies were also identified in coastal waters, such as in San Diego Bay. Francisco and in the North and South Atlantic, including Brazil.”
Despite the low concentrations, there are several studies trying to verify the toxicity of the group of rare earths in relation to organisms present in rivers and sediments, according to Bruno Mortatti. “Not much is known about it yet. For humans, in principle, gadolinium is not a threat, as its chelates are stable in the environment for several months. But the effects of its continuous and increasing introduction into ecosystems are still insufficiently known and studied.”
Jacinta Enzweiler reports that, in addition to gadolinium, researchers have already found anomalous amounts of lanthanum and samarium in river water in Germany, the first of which is associated with the production of catalysts used in oil cracking. “The large number of applications of rare earth elements suggests that their anthropogenic addition to the environment will continue.”
The research author adds that, because of this recent and increasing introduction into the environment, rare earth elements are also considered emerging contaminants. “If studies are not carried out to monitor them, we will superimpose this man-made signature with the signature of the natural environment itself, without distinguishing one from the other. Studies like this one in the thesis serve to understand their natural distributions and obtain parameters to assess whether or not there has been anthropic addition.”
water security
This doctoral thesis also provides support for a thematic project still under analysis by Fapesp: the Brazilian Water Research Center, which involves Sanasa (Water Supply and Sanitation Society of Campinas) and several Unicamp units. The person responsible for the project is Professor Lauro Kubota, from the Chemistry Institute (IQ), and professors from the Geosciences Institute participate in it, including Sueli Yoshinaga Pereira and Ana Elisa Silva de Abreu. There are three focuses: water security, with the IG responsible for studies such as the quantity of water and basins; water quality, which requires IQ's attention to water and sewage treatments; and distribution engineering, by FEC and FEEC. The idea is that the Water Research Center will be a large pilot project to raise water quality to international levels.
Currently, the drinking water distributed by Sanasa depends on the Atibaia River and, to guarantee water demand, the first reservoir is under construction, on the Jaguari River. The quality of the water collected determines the type of treatment required and its cost. “We will work with two sub-basins: the Pinheiros stream (a tributary of the Atibaia river) and the Cachoeira stream (part of the area studied by Bruno Mortatti)”, says professor Sueli Pereira. “There are two basins with different characteristics, one very urbanized and the other in an agricultural area. The objective is to assess water availability in these basins, taking into account current demand in a conurbated and constantly growing region.”
Professor Ana Elisa de Abreu, in turn, notes that this is a large project, with the collaboration of researchers from different areas at Unicamp and that the role of the IG will be to offer a regional, integrative view, on a basin scale, while other teams will have a more specific focus, for example, on water and sewage treatment systems. “Here the link with the work of professor Jacinta and Bruno Mortatti, who focuses on basic science. Without data like those raised in the thesis, without understanding how the rock affects the chemical composition of the water, we will not be able to evaluate long-term scenarios, such as simulating the availability of water in a few decades, as foreseen in the project. And a special effort will be to include groundwater in the availability account.”
Sueli Pereira explains that a trend in large universities abroad is to work in an integrated manner on land use and occupation, climate, climate change, surface water and groundwater. “All this to promote water security, which, in turn, is closely linked to food security: to produce food you need water. We have methods for predicting the availability of groundwater, but not in an integrated way, as this requires technological development, that is, numerical models.”
According to the teacher, the Pinheiros river basin is a priority for Sanasa, as it contributes to the Atibaia river having sufficient flow to supply Campinas. “The stream flows into Atibaia, where the water is collected for the water treatment plant in the district of Sousas and, from there, the treated water is distributed to the majority of the city's population. The Pinheiros stream basin presents conflicts between surface and underground water, with many impermeable areas and subdivisions. Therefore, it is one of the IG’s focuses on the project.”
