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Water, a resource under examination

The largest water reservoir of South America might have excess radioactivity

The immense fountain of underground waters called the Guarani Aquifer, a resource little publicized by the countries of the Mercosul, has been the object of studies which should help its preservation and safe use by the populations of the vast area which it covers. The quality of the water is considered good in many areas, but the physicist Dr. Daniel Marcos Bonotto, Professor of Geochemistry at the Institute of Geosciences and Exact Sciences of the São Paulo State University (Unesp – the Portuguese acronym) in Rio Claro, points out some problems.

In various wells, he has found excessive levels of the radioactive elements radon and radium, associated with lung and stomach cancer. Another conclusion is that in the less deep zones the underground reservoir is being contaminated by the leftovers from the pork industry, from coal mining and toxic products of industrial and agricultural origin. “We found even an increase in the level of nitrates in the water of a well in Ribeirão Preto, and the source is untreated sewage.”

One of the largest subterranean reservoir in the world, the Guarani Aquifer extends over an area of 1.2 million km². Two thirds of it are in Brazil, parts of the States of São Paulo, Minas Gerais, Mato Grosso, Mato Grosso do Sul, Goiás, Paraná, Santa Catarina and Rio Grande do Sul, and the remainder in the north of the Argentina, the east of Paraguay and the north of Uruguay. The area is equivalent to the total territory of Peru, Spain, France and Great Britain.

The reservoir is estimated to contain 50,000 km³ of fresh water, enough for the whole world for ten years. Its use for human consumption must be based on studies that attest to its potability or point to the necessity of a pre-treatment. In Brazil, the researches carried out on the reservoir were developed above all from the 70’s onwards by the Department of Water and Electrical Energy (DAEE the Portuguese acronym) of the State of São Paulo.

However, there is still a lack of more precise hydrogeological data about these reserves. For this reason, Brazil and the other countries of the Mercosul began in 2001 a project to produce an in-depth study and to create a model for the administration of the use of the waters of the aquifer and for its environmental protection. The project has the support of the World Fund for the Environment (Global Environment Facility – GEF) and will be able to count on investments of US$ 25 million from the countries involved until 2005.

Radiation and pollution
Dr. Bonotto has been working since 1991 on a radiometric investigation – the detection of radioactivity, of the aquifer with the help of the National Council of Scientific and Technological Development (CNPq) of the Ministry of Scienceand Technology; of the International Atomic Energy Commission (AIEA) in Vienna and of FAPESP, which has already liberated resources for three projects, including an investment of US$ 47,700 for the purchase of equipment and the modernization of the laboratory.

The signs of radiation became evident after nine years of field work (see box). The researcher collected and chemically analyzed, three times each, 80 samples of subterranean water of tubular artesian wells in almost 70 cities and towns in the States of São Paulo, Mato Grosso do Sul, Paraná, Santa Catarina and Rio Grande do Sul. The selection of the wells was made in collaboration with DAEE (The Department of Water and Electrical Energy) in São Paulo and Araraquara and with the Research Company of Mineral Resources (CPRM) in São Paulo and Porto Alegre. The researcher also took into account information generated from similar studies carried out at the Institute of Geosciences of the University of São Paulo (USP) under the coordination of Professor Aldo da Cunha Rebouças, considered to be one of the best authorities on the question.

For Dr. Rebouças, the data might not be representative, given the possibility of contamination within the laboratory. He thinks it would be advisable to collect a new series of samples from each well to prove the analysis. Dr. Bonotto does not believe in the possibility of contamination within the laboratory and evaluates that, in the case of the radioactivity, the values found could even be an underestimation, due to the losses that occurred in the process.

Anyhow, as the partial results show that the reference value of the radioactivity is high in many municipalities and this could mean that the use of the waters of the aquifer for human consumption in some localities is endangered. Dr. Bonotto considers it fundamental to have an effective radiometric control by the sanitary organs responsible for the distribution of water to the population and the definition of the regions where the water is appropriate for consumption, for bathing and for agriculture.

For him, the sampling is good and representative, but he believes that there is a need to analyze the water of the 15,000 tubular artesian wells which take the water from the Guarani Aquifer, many of them at a greater depth than 1,000 meters. More or less 200 municipalities in the São Paulo State get their water totally or partially from the reservoir, which is also used in irrigation, and in the food, drinks and textile industries.

Dr. Bonotto is also worried about the abusive exploitation of the reservoir. “If we drill a lot or take out too much water, the ground may accommodate and erode.” He believes that the use of the subterranean water has to be controlled. “We have to carry out a study to know the quantity of water that can be taken from the reservoir, mainly because the extraction basins are concentrated in some regions and not in others.”

The measurements and the necessary cautions

In the case of uranium, Dr. Daniel Bonotto confirmed that the average radioactivity of the 80 samples of water analyzed is well below the maximum level recommended, which proves the potability of the water in relation to the isotopes of uranium U238 and U234. However, in some samples heavy metals such as cadmium, considered to be cancerigenic, were found. It was identified in the water of a well 124 meters deep, used as a water supply by the Company of Basic Sanitation of the State of São Paulo (Sabesp in the Portuguese acronym). In that well, the level of cadmium exceeded by 20 times the maximum limit established by the Special Technical Law (NTA-60) about water for general consumption in the State of São Paulo, approved by the State Decree No 12,486.

Concerning radon, the researcher found elevated levels in the waters of the majority of the wells analyzed. As there is not any Brazilian legislation about the intake of radon, Dr. Bonotto compared the results with the limits of 300 pCi/l (pico Curies per liter) proposed in 1991 by the Agency for the Environment Protection of the United States (Usepa). More than half of the wells analyzed, including some used for human consumption, overstepped this limit.

There were high levels of radon in the waters of the wells of Maringá (3,303 pCi/l), Londrina (2,453 pCi/l) and Cornélio Procópio (2,408 pCi/l) in Paraná, but none of them was used for human consumption. In São Paulo, however, water from the wells used for human consumption revealed the levels of radon to be superior to the limits established by international legislation in Fernandópolis (2,902 pCi/l), São José do Rio Preto (1,272 pCi/l), Catanduva (1,272 pCi/l), Lins (1,516 pCi/l) and Ribeirão Preto (718 pCi/l).

Dr. Bonotto plays down the threat with the comment that the half-life, the time that radioactive material takes to disintegrate to a half of its original quantity, for radon is at the maximum four days. Also, when the water is treated or even only stored in large water tanks, as it often happens, there is a process of aeration that diminishes the levels of radon, eliminating the risks of radiation. Dr. Aldo Rebouças added that as the half-life of radon is very short, by the time that the water is consumed by people the radon gas has already disappeared. Nevertheless he agrees that it is necessary to carry out treatment in the case of the water which is taken from an artesian well and channeled immediately into the network for distribution. Even then, according to the researcher at Unesp, even when the radon disappears from the waters stored in reservoirs or tanks, radioactive lead could remain, which is one of radon’s offspring.

As the level of radon is high, Dr. Bonotto suspects that the element from which it originates, radium, could also be high and he took another sample collection from the 80 wells. The analyses confirmed his suspicions in some wells, with levels of radium up to four times higher than the maximum limit established by Brazilian legislation for the total emission of alpha radioactivity by radioactive elements, among them radium226.

Dr. Bonotto explains that radium has a high degree of radioactive toxicity, a large tendency to fix itself into our bones, a long half-life of 1,622 years and a high potential to produce biological damage as it is gives off alpha radioactivity. According to him, the maximum concentration of radium226 in the waters suggested by the World Health Organization (WHO), is of 1 Bequerel per liter (Bq/l). The criteria put into place in Brazil is based on the Judicial Directive N° 36 of the 19th of January 1990 from the Ministry of Health, which established the reference value of 0.1 Bq/l (close to 2.7 pCi/l) for the total alpha radioactivity and of 1 Bq/l for the total beta activity.

The levels found in the samples of some wells are above the limits suggested by the WHO and well in advance of the maximum value of 0.1 Bq/l for the total alpha radioactivity in water, which includes radium, established by Brazilian legislation. In São Paulo, the researcher verified, for example, that the level of radium in a well in Catanduva is of 1.8 Bq/l, almost twenty times above the level permitted by Brazilian law . In a well in Monte Alto the level of radium was of 0.7 Bq/l, in Ribeirão Preto of 0.5 Bq/l and in São Simão of 0.5 Bq/l.

The Projects
1. Radium in the Guarani Aquifer (nº 99/10991-5); Modality Aid to research project; Coordinator Dr. Daniel Marcos Bonotto – Unesp of Rio Claro; Investment R$ 30.136,20
2. The Geochemical Behavior of Radon in the Subterranean Waters of the Sedimentary Basin of Paraná (nº 97/12527-9); Modality Aid to research project; Coordinator Dr. Daniel Marcos Bonotto – Unesp of Rio Claro; Investment R$ 11,000.00