Arsenic in water: an invisible foe

The Andes mountain range was formed 50 millions of years ago, as a result of the plate tectonic movements. This fact led to consequences that remain nowadays: during the process, great quantities of volcanic ash with high levels of (As) and fluoride. Currently, these materials are part of the loess or sediments of groundwater aquifer. The arsenic is the main natural pollutant of the groundwater, which is the only source for human consumption in a large area of our country. This problem, which produces a marked effect on the social health and economic sectors of the affected regions, involves more than eight millions of people.

According to the World Health Organization (WHO), arsenic is one of the ten chemical substances most worrying for public health. This organization established recommended limit for its concentration in drinkable water at 10 parts per billion (ppb). The consumption of water with higher concentration causes a disease called Chronic Endemic Regional Hydroarsenicism (“HACRE” in Spanish) which was characterized by skin lesions that evolve to affect liver, renal and respiratory functioning. Furthermore, arsenic proved to be carcinogenic.

Considering this problem, since 2006 members of Research Centres of CONICET in Salta and La Plata have studied the development of systems to remove arsenic in groundwater to avoid its negative impact on the inhabitants of the Llanura Chacopampeana and the northeast of the country.

Science in search of solutions

“In Argentina, all the central part of the country, from Paraná River to the Andes has this problem. It is necessary to eliminate arsenic and we found a simple and cheap method. But we cannot talk about profitability because there is something invaluable: people’s lives” Horacio Thomas, CONICET senior at the Centro de Investigación en Ciencias Aplicadas “Dr. Jorge J. Ronco” (CINDECA, CONICET-UNLP) [Applied Sciences Research Centre “Dr. Jorge J. Ronco”].

The research team conducted its studies in the province of Buenos Aires, where 87% of the territory has concentrations higher than 50ppm. The chemist explains that in 2006, they began to research into the issue from the question of a doctor who worked at public hospital in the southwest of the province, where she realized that there is a higher proportion in the statistics of patients with HACRE.

This interdisciplinary activity was directed by Horacio Thomas, who is also director of the Planta Piloto Multipropósito (PlaPiMu, CICPBA-UNLP) [Multi Purpose Pilot Plant], Isidoro Schalamuk, CONICET senior researcher (R) and director of the Instituto de Recursos Minerales (INREMI, CICPBA-UNLP) [Mineral Resources Institute] and Lía Botto, CONICET principal researcher (R) and member of the Centro de Química Inorgánica (CEQUINOR, CONICET-UNLP) [Inorganic Chemistry Centre]. Furthermore this activity led to the treatment strategy for the removal of arsenic through natural species adsorption. The study began with the search for different minerals, their physical, chemical and mineralogical characterization and analysis of their potential in removing the contaminant already mentioned.

The adsorption is a phenomenon in which a solid substance attracts and retains different chemical species at its surface. This is one of the most convenient and simplest technologies to eliminate a water-soluble substance, what is particularly useful for the treatment in waters in rural and/or sanitary deprived regions. The researchers studied the adsorption capacity of different abundant and low cost natural aluminosilicates until they found the use of a mineral from clay, rich in iron that comes from deposits of the province of Buenos Aires. This study was undertaken at the IREMI. Once the mineral is characterized and the scientists of the CEQUINOR in PlaPimu assessed its retention capacity in the laboratory, the researchers analyse, at pilot level, the scale-up and design of treatment plants of 2-4 thousand litres that were obtained through a subside. These plants were built and installed in rural schools located in Punta Indio, Casares, Bolívar and Pigüé. The aim was to meet the needs of the schools and neighbours.

“The pilot plant has three tanks. The first one is the reactor where we place the adsorbent and water, plus additives such as the chlorine which ensures the microbiological quality of the water and guarantees the oxidation state As5+ and a flocculant that reduces the solids in suspension, therefore controlling water turbidity. In the second tank, the sedimentation process is completed and the currently established values of turbidity are achieved so as to finally pass through a third storage tank. At the schools, the tank has a direct connection with the kitchen, it does not need special staff to operate it”, the researcher explains.

Pilot plants use a ratio of clay/water of 1:10 for treatment, achieving values of arsenic and fluoride established by international standards. With its daily use, the adsorbent has proved to have a lifespan of approximately six years, after which a sustainable waste disposal is carried out. “Scientists at the Entrenamiento Multidisciplinario para la Investigación Tecnológica (LEMIT) [Laboratory for Multidisciplinary Training in Technological Research] studied the definite immobilization of contaminants so as to use suitable processes to prevent the return and facilitate the manufacture of useful elements in the construction. Leaching tests, solid-liquid extraction, were negative confirming the sustainability of the process”, Thomas affirms.

Arsenic in Salta

In the province of Salta, a research team lead by Mónica Farfán Torres, CONICET independent researcher at the Instituto de Investigaciones para la Industria Química (INIQUI, CONICET-UNAS) [Chemical Industry Research Institute], studies another alternative to remove this compound in water. The scientist explains that arsenic is found in the areas of Puna and Chaco Salteño and not in Valle de Lerma and Valles Calchaquíes – where most of the population lives- because they have another type of geological formation.

In 2006, a Proyecto de Investigación Científica y Tecnológica Orientado (PICTO)[Oriented Project of Scientific and Technological Research] of the The National Agency for Science and Technology Promotion at the NOA to improve the quality of life of the Llanura Chaqueña, which comprises the provinces of Formosa, Chaco, Salta, and a small part of Tucumán and Santiago del Estero.

“It is an arid region of sand and open roads that can remain isolated up to six months due to the rains. It is hard to reach because there are vulnerable and scattered villages, hamlets that crowd around schools or farms and maintain a system of subsistence. The water they consume comes from national wells that were dug in the nineties, some of them with a depth of 393,70 feet. We identified areas with very high levels of arsenic, the limit in Argentina is 0.05 mg/L and the places that had the lowest value were 0.13 or 0.20 mg/L, that is to say, they quadruple those values. The average is 0.25 mg/L”, Farfán Torres states.

Furthermore, beyond the cancer cases detected in the villagers, the researcher explains that they found many children neurologically infected because the main damage of the arsenic is to cross the placenta during pregnancy and affect the fetal brain development
“We developed a removal system which is a series of tanks. One of them has a rudimentary filtration system that consists in sand and activated carbon and an active phase which is iron provided by conventional materials such as wires or nails. In 2009, two of these teams settled in two schools: Siervo Cansado and Tres Horcones. The Mesa Provincial de Arsénico (MEPROAS) [Provincial Arsenic Board] monitored the teams during a year to check how they worked. At that moment, they installed the system in eleven more schools in the province and now they are building other ten more equipments”, Farfán Torres explains.

The team provided previous training to let temporary isolated populations know that every sis months they have to change the iron load and part of the filter bed, the layer of sand. The sand with the still arsenic is also used to build blocks for construction. “The system is very simple, villagers can maintain it without help, they know the time of the year when they have to make the change and they have their reserve. We aim to provide an easy technique to let people operate the system autonomously”, the scientist comments.

The interdisciplinary teams of La Plata and Salta have projects to develop changes in their respective systems so as to make the benefits of their projects reach more people. In La Plata, the research team built an automated home equipment that produces 100 l/day and work in the scale-up to provide water in medium populations. In the case of the team at the INIQUI, the scientists plan to produce home systems with equipments that adapt to the needs of the isolated populations of Puna. It would be enough to create a system that produces between 20 and 40 litres per day for 2 to 4 inhabitants a house.

Considering water as the main fuel in life and aiming to ensure water quality for everyone, these technological strategies represent great advantages because they enhance the quality of life of more and more people who live in deprived areas. Besides, it is cheap, accessible, easy to implement and maintain.

“In one of the first visits, one community chief told me: ‘I think it is fine that you come here and measure us, but what I really need is that you eventually do something for us with all the results.’ After the development I notice that they are satisfied with it and they are not afraid of what could happen to their children. This is more satisfactory than any other publication. This is the most important achievement in my career”, Farfán Torres comments. For his part, Thomas adds: “It is a way to show society that our work as researchers aims to solve current problems. We did not produce a system to be awarded a Nobel Prize; we took knowledge from different sources to create the system. We are very proud of it.”