Concentrations of arsenic and fluoride have doubled in the Lerma-Chapala aquifer

As if drought conditions in many parts of Mexico weren’t enough, the levels of pollutants found in tap water are reaching worrisome levels, according to the results of a study by the National Autonomous University of Mexico (UNAM).

The Geosciences Center (CGeo) at UNAM has found that the concentrations of arsenic and fluoride in the Lerma-Chapala aquifer have doubled during the last 14 years, and underground water sources in Querétaro, San Luis Potosí, Aguascalientes, Zacatecas, Durango and Sinaloa face similar challenges.

The Lerma-Chapala aquifer extends over 7,000 square kilometers, from the State of México, through El Bajío and into the state of Jalisco.

Researcher Marcos Adrián Ortega Guerrero from CGeo, who has been monitoring the watershed since 1998, said that “all observed aquifers, in a lesser or greater degree, present the same issues, and they only tend to worsen.”

In 2001, Ortega said, arsenic and fluoride were found in an area of 500 square kilometers of the Lerma-Chapala system, in concentrations 10 times greater than what are deemed tolerable limits for human consumption.

“According to recent measurements, that area has expanded to 800 square kilometers; concentrations [of pollutants] have doubled in some places, and arsenic — a carcinogen — has been recorded at 20 and up to 30 times over its acceptable levels,” said the researcher.

“Arsenic is generating cancer issues among the population. Fluoride has gone from affecting teeth and the skeleton to being associated with neurotransmitter issues, reducing the intelligence quotient of children by between 40 and 50%; children stop learning, and that’s irreversible,” continued Ortega.

This contaminated underground water reaches tens of thousands of households and businesses in the region through drinking water networks in an area classified as the aquifers of La Laja river and Laguna Seca, known by specialists and people of the region as the “independence watershed.”

The name was chosen because its towns, which are those most affected by the pollution problems, are iconic for their involvement during the Independence War of 1810-1821: Dolores Hidalgo, San Miguel de Allende, San José Iturbide, Doctor Mora, San luis de Paz and San Diego de la Unión. Celaya and Irapuato have been recently added to that list, as high levels of arsenic and fluoride had been registered there, too.

Ortega said that water containing arsenic, fluoride, aluminum and other elements comes from deep flows “that ascend to the aquifer proper,” a process he said is caused by over-exploitation of the watershed.

The state of water reserves is less than optimal throughout the country, as an assessment made by the Federal Auditor’s Office (ASF) revealed in 2011.

That assessment gave a negative grade to water quality, both underground and surface. The former presented higher salt levels than recommended, while 61% of the latter was polluted by fecal matter and other substances.

Aquifers with this problem are located in the states of Durango, Zacatecas, San Luis Potosí, Baja California, Sonora, Hidalgo and México, although the National Water Commission, Conagua, has determined that high salinity is to be expected in the cases of Sonora and Baja California, due to their proximity to the sea.

In the case of surface water sources, such as rivers, lakes and lagoons, the ASF determined that all 13 hydrologic-administrative areas presented contamination by “oil, plastic and pesticides,” while in eight, or 61%, water had been affected by “fecal matter, parasites and bacteria.”

Even if some level of contamination is to be expected in those water sources, the measured concentrations exceed health parameters established by law.

What’s worse, experts agree that surface waters can filter into underground reserves, along with all the contaminants they carry.

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