The poison that was once used to eliminate monarchs is now a potential health problem in several regions of Mexico due to its presence in water.
Although no one can accurately estimate the number of people exposed to arsenic nationwide—or the true burden of disease it causes—in 2001 it was estimated that between 400,000 and 2 million people were at risk due to high concentrations of this toxic element in water.
The estimates from the most recent studies (2021) estimate that at least 8.81 million people are at risk due to the presence of arsenic above the limit recommended by the World Health Organization (WHO).
For Dr. Francisca Alicia Rodríguez, an academic and researcher at FES Cuautitlán, the situation will continue to worsen in the coming years: on the one hand, the population continues to grow, on the other, in response to the water crisis, water is currently being sought in deeper wells, where the risk of contamination is greater.
“There are two ways in which arsenic can be incorporated into aquifers, one is naturally, due to rocks. Another is due to human activities, such as mining or the use of pesticides. Over time, the concentration of arsenic [in wells] may be greater,” she says in an interview with MILENIO.
Why it is dangerous
Constant exposure to arsenic, known as the ‘king of poisons’, can be through drinking water and contaminated food.
When a person suffers severe poisoning, it manifests itself with vomiting, abdominal pain and diarrhea, as well as numbness, tingling, cramps and it can even cause death.
In cases where exposure occurs over the long term — with concentrations greater than 10 mg per liter — skin lesions can occur, such as thickening and discoloration of the skin.
Some research indicates that it also increases the risk of cardiovascular diseases, diabetes, obesity as well as disorders in the reproductive, nervous, immune, liver and lung systems.
In addition, they are capable of leading to cancer of the breast, bladder, lungs, skin, kidneys, liver and prostate.
THE FACT
The water problem in Zimapán
The Zimapán Valley (Hidalgo) is a semi-arid area where concentrations of arsenic in groundwater and soil have been detected that are higher than the international standard.
Naturally occurring arsenic minerals in the region, combined with fumes from smelters that operated in the Zimapán area, are partly responsible for carrying arsenic and contaminating shallow wells. Mining waste and tailings also act as another source of contamination.
Which states are most exposed?
In Mexico, the highest concentrations of arsenic in water are found in specific regions in the north of the country, in states such as Chihuahua, Coahuila, Durango and Sonora.
A study published in Nature in mid-2023 revealed that 1.75 million people in La Comarca Lagunera (made up of seven municipalities in Coahuila and Durango) are exposed to arsenic levels higher than those established by the WHO guidelines.
The analysis found that residents with greater exposure to this substance had a higher risk of obesity, type 2 diabetes, and hypertension.
Other states that also have red dots on their map are Aguascalientes, Guanajuato, Jalisco, Morelos, Oaxaca, Puebla, San Luis Potosí, Hidalgo, and Zacatecas. There is a high probability that more regions will be added to the list in the future.
“Something that catches my attention is that in the State of Mexico and the metropolitan area there has been a shortage of water, so we have to go to deeper wells, so obviously the quality is different. Due to the composition we can be exposed to arsenic,” adds Rodríguez Pérez.
What is the main source of arsenic exposure?
Arsenic is found naturally on Earth, so there is more than one way in which people can be exposed.
The movement of tectonic plates and the erosion of rocks are natural ways by which arsenic reaches water and food. However, its popular use in pesticides, mining activity and industrial processes also add to the exposure burden.
The alternative: How to remove the poison from water?
Recently, Dr. Francisca Alicia Rodríguez Pérez and her team developed a promising method that seeks to remove the poison from groundwater.
This is electrodeionization, a process that combines two completely different techniques to extract traces of the element suspended in water. On the one hand, electrodialysis consists of using a membrane, which acts as a kind of selective strainer that will only let arsenic ions through.
Once the arsenic has been isolated, the second method is applied: small spheres, better known as ion exchange resin, are used to ‘capture’ it.
Applying both processes not only reduces energy use but also allows scientists to avoid generating waste and to dispense with alternative chemical substances, thus making the process more environmentally friendly.
The laboratory work has had good results, and the permitted limit of arsenic in water has been reached during the tests. The current challenge is to take it to a large scale. For now, the engineer and her team are already doing the calculations for this.
“Our objective is not only to treat it here at the pilot plant level in the Chemical Engineering laboratory, but to be able to take it to treat large quantities,” explains the expert.
Once this is achieved, the project could be implemented in places where the problem exists: dams, wells, etc. This would require cells that are as compact as possible, which can treat water in large quantities without losing practicality.
Given the characteristics of the process, the cells could be used not only to capture arsenic, but also heavy metals, contaminants and salts.
“We have worked with brackish water [a mixture of salt and fresh water] and sodium and chloride ions have been removed. We have also removed chromium, which is widely used in the cultivation of leather. We can also remove nickel, cadmium, antimony, chlorine. As long as it is in ionic form and soluble in water, it can be removed,” says Alicia.
Recently, Dr. Rodríguez Pérez and her team took samples from the Zimapán dam, a point located between Querétaro and Hidalgo where high levels of arsenic have been recorded.
Although it was a small amount of water, the results showed that the process is not only effective in reducing the concentration of arsenic, but also other elements.
Source: milenio
