The Atoyac River: A Troubling Case of Pollution
The Atoyac River ranks among the most polluted waterways in Mexico. Flowing through the states of Puebla and Tlaxcala, this river traverses industrial zones, urban areas, and wastewater treatment facilities, accumulating heavy metals, detergents, and organic matter along its journey. Compounding this issue, pharmaceutical compounds have also been identified as significant contaminants.
A recent study published in The Journal of Environmental Management investigated 45 pharmaceutical compounds found in the waters of the Atoyac River and its primary tributary, as well as in the Valsequillo Dam. Among these compounds are various antibiotics, analgesics, anti-inflammatories, and psychiatric medications.
The research highlights the varying concentrations of these substances in the river’s surface waters, noting that the highest levels were detected downstream from wastewater treatment plant discharge points and in densely populated areas.
Researchers assert that these contamination hotspots underscore the detrimental impact that poor wastewater management can have on water quality, as well as on local ecosystems and the health of communities in this region of Mexico.
Wastewater Treatment Plants: A Key Source of Pharmaceutical Contamination
The source of the Atoyac River, located at the foot of the Iztaccíhuatl volcano, is the least polluted part of the river, having not yet come into contact with urban settlements or industries. While pharmaceutical compounds can originate from various sources, the primary contributors are urban wastewater and hospital effluents, according to the study.
Jaime Dueñas Moreno, a research professor at the Tecnológico de Monterrey in Puebla and a co-author of the study, emphasises that conventional treatment plants are not designed to eliminate such compounds. He explains that inadequate management of wastewater can exacerbate the concentrations of these contaminants within the river.
“In conventional treatment systems, contaminants can be redistributed during the process. Some end up in the effluent while others accumulate in the sludge. What is critical to note is the impact of treated, untreated, or inadequately treated wastewater discharges,” Dueñas elaborates.
The study identified the presence of various compounds such as ibuprofen, diclofenac, sulfamethoxazole, and naproxen, which exhibited differing levels of ecological risk, particularly in regions with wastewater discharges.
Concerns Over Hard-to-Degrade Pharmaceuticals
Abrahan Rafael Mora Polanco, also a research professor at the Tecnológico de Monterrey in Puebla and a co-author of the study, notes that they discovered pharmaceuticals that are difficult to degrade, which may pose health implications. “We found carbamazepine, an antiepileptic drug that is notoriously difficult to break down, and sulfamethoxazole, an antibiotic. The concern is that the water from the Atoyac River is used for irrigation,” he states. He adds that assessing the impact requires evaluating the concentrations of these compounds in aquifers and whether they reach crops irrigated with Atoyac water.
“Clearly, this poses health implications, but the concentration of these compounds in aquifers has not been evaluated. We are conducting preliminary studies on the Atoyac River,” Mora explains.
The investigation underscores prior ecotoxicological studies which indicate that even at low or moderate concentrations, active pharmaceutical compounds can adversely affect aquatic biodiversity, leading to reproductive behaviour alterations, hormonal system disruptions, and even the development of antimicrobial resistance.
The Broader Implications for Ecosystems and Human Health
Regina Montero Montoya, an academic at the Institute of Biomedical Research at UNAM, asserts that the most environmentally toxic active pharmaceuticals are antibiotics, intended to eliminate bacteria, along with antiparasitics. She warns that these substances can indeed impact regional ecosystems.
“They can start inhibiting biological functions in organisms that inhabit the river, leading to changes in the composition of biota and the frequency or abundance of certain species. The most concerning aspect is that those species able to withstand these conditions will survive,” Montero explains.
Although the study primarily focused on identifying pharmaceutical compounds and did not evaluate their direct impact on human health, Jaime Dueñas highlights a crucial finding regarding the detection of antibiotics such as trimethoprim, ciprofloxacin, and sulfamethoxazole in the Atoyac River, which may encourage the development and spread of antimicrobial resistance.
“When these antibiotics are present, microorganisms can develop resistance, leading to collateral damage, especially considering that the water is used for irrigating crops,” says the researcher, who specialises in monitoring contaminants in water bodies.
Montero, who has studied the river for over 20 years, concurs with this phenomenon, attributing it to human activities affecting water bodies.
Complexities of Contaminants and the Need for Further Research
The study also examined water from the Valsequillo Dam, one of the largest water bodies in the region, which is primarily fed by the Atoyac River. Mora, who investigates organic and inorganic contaminants in the hydrological system, explains that several hard-to-degrade pharmaceuticals were identified in this dam, which also supplies water for irrigation.
“The Valsequillo lagoon retains water for irrigation, but there are some compounds that are extremely difficult to degrade, such as carbamazepine and sulfamethoxazole. These compounds could potentially reach the crops,” he asserts.
Dueñas emphasises the necessity for further research on this potential connection, aiming to generate scientific evidence that could inform environmental regulations regarding these substances. “Even if treatment systems exist, if regulations do not address antibiotics, attention may not be given to their removal despite the environmental issues they may cause,” he remarks.
Broader Risks Beyond Pharmaceuticals
The authors of the study also highlight that the compounds found at various points along the Atoyac River represent a lower risk compared to the extensive presence of bacteria, which can reach alarmingly high levels, alongside industrial waste.
“What we discovered poses a risk, yet it is the least significant risk. The primary threat from the river is a mix of bacteria capable of causing diseases. Biological agents are likely to trigger immediate problems, while chemical contaminants may pose long-term risks; however, the urgent concern for the river is biological risk,” Mora clarifies.
Montero stresses that treatment plants must now adopt modern technologies to effectively remove these substances, particularly from industrial and hospital effluents. “There are various methods available for treating water and removing chemical substances, including coagulation, flocculation, sand filtration, activated carbon, reverse osmosis, ion exchange, and techniques to eliminate bacteria such as ozone, chlorine, or ultraviolet light,” she elaborates.
For her, the study provides crucial information that should not be disconnected from the ecosystems dependent on the river, as she warns that the biodiversity of the area is at risk. “This vast array of chemical compounds may not all be highly toxic, but if they are active, they interfere with the natural biological processes of living organisms. We may witness declines in populations of native species such as axolotls, frogs, and fish,” she cautions.
For the study’s authors, the discovery of pharmaceutical concentrations, particularly antibiotics, is a significant contribution to understanding emerging contaminants in one of the country’s most polluted rivers.