Water, Agriculture, and Public Health. Invisible Pesticides in the Santiago River

Behind the “dark” water that can be observed in many rivers, which in colloquial terms we call “dirty,” there are various chemical substances that represent an environmental risk. One of the most valuable resources for life is water. Human health, food production, and the balance of ecosystems depend on it. Likewise, in many parts of the world—Mexico is no exception—water bodies are affected by growing urban discharges, industrial waste, and agricultural runoff. Pesticides, which are used to prevent crop infestations, are among the most alarming chemical pollutants because when they reach rivers they represent a serious danger to people’s health.

The Santiago River in Jalisco is an example of this environmental situation. The basin is influenced by urban, agricultural, and industrial activities of great economic relevance, but it has been exposed as one of the most polluted in the country (Bollo-Manent, Montaño & Hernández, 2017; Jiménez Hernández, 2023). Several studies have recently identified, in addition to traditional pollutants, pesticides in low concentrations, that may have adverse effects by their toxicity, their persistence, and their bioaccumulation capacity (González-Díaz et al., 2025; Muñoz-Delgado et al., 2025; De Anda et al., 2024). Considering this problem, this article addresses the issue of pesticides in surface water of the Santiago-Guadalajara River, as well as their possible implications for health and the relevance of international scientific collaboration to face this type of environmental challenges.

Río Santiago en Jalisco.
 Rosa Leonor González-Díaz

ALLIES IN THE FIELDS, ENEMIES OF WATER
Over the years, pesticides have played an important role in increasing yields in agriculture and crop protection. Their use in Mexico has experimented an accelerated growth, especially in regions with commercial agriculture, such as the West of the country. A significant part of these compounds not only remains in fields and soils but is also carried by irrigation and rainfall to streams, dams and rivers, causing pollution.

Characterized by being one of the states with greatest agricultural activity, Jalisco has a challenge in developing sustainable alternatives for food production; a great challenge due to the constantly growing demand. Much of the residues of pesticides used in agriculture end up in water bodies such as the Santiago River, where organochlorine and organophosphate groups predominate. Some of the compounds—Lindane (gamma-BHC), Aldrin, DDT, Endosulfan and Dicofol—previously identified (De Anda et al., 2024)are banned today or severely restricted in many countries due to their environmental persistence and to their toxic effects on health, and are part of the list of persistent organic pollutants of the Stockholm Convention [see box].

It has been documented that such compounds in rivers in Latin America, Asia, and Europe are linked to severe damage to the central nervous system, effects on the immune system, hormonal changes, and increased risk of cancer (Elumalai et al., 2025; Li et al., 2024; Meena et al., 2025). In Mexico, these contaminants have also been found in food, soil, and drinking water, which confirms the serious national problem they represent.

SANTIAGO RIVER UNDER THE SCIENTIFIC MAGNIFYING GLASS
Recently, an analysis of the presence of pesticides was carried out in 25 monitoring stations located along the Santiago-Guadalajara River basin (figure 1). Among the compounds identified, more than ten stood out, which are known for their ability to accumulate in organisms over time and for their toxicity.

 Elaborado por Rosa Leonor González-Díaz 

This study not only quantified the concentrations of pesticides in river water, but also sought the answer to a key question: What do these values mean for people’s health? Risk assessment methodologies were developed with emphasis on infants, children, and adults. The hazard quotient (HQ) compares how much pesticide may be entering the body with an amount considered safe. If the value obtained is less than one, the risk is usually low; if it exceeds that value, there is a potential health concern. The hazard index (HI) sums up all the HQ of the different pesticides detected in the water and shows their combined effect because in real life we are not exposed to a single pollutant but to a mixture. Total cancer risk (TCR) was also estimated, which expresses the probability that a person can develop cancer after continuous long-term exposure. A TCR value of one in a million indicates very low risk, while higher values may be considered concerning and require attention.

The results obtained showed an important spatial variation between seasons and periods. Although many points of the river showed low values (HI less than one), two of the stations analyzed exceeded this threshold level, which represents a potential risk to public health, especially in riverside communities. These zones are located near areas with intense agricultural and urban activity.

CHILDHOOD AT THE CENTER OF THE PROBLEM
The situation for infants and children under this scenario is very worrying. In one of the stations, the HI reached values above four, mainly highlighting high concentrations of Dicofol. The physiology of this group is more vulnerable due to lower body weight, higher relative water consumption, and a developing immune system, factors that make it more susceptible to environmental pollutants. In other agricultural regions of Jalisco, such as the Ayuquila River basin, high concentrations of pesticides have been reported.

For this reason, the infant group is usually one of the most vulnerable to environmental contamination by these pollutants in the water. Babies and children can absorb proportionally more pesticides than adults. A partial or prolonged exposure can have implications years later, and have been linked to endocrine disruption, associated with learning disabilities, neurodegenerative diseases, and an increased chance of certain kinds of cancer (Sarailoo et al., 2022). When pesticides are found in surface water, there’s a risk of entering the body through direct consumption from runoff that goes into water wells, domestic use, or through the food chain. This last point is associated with the contamination present in edible fish, as well as in vegetables that have been irrigated with contaminated water in zones near the basin.

THE GLOBAL DIMENSION OF A LOCAL PROBLEM
The presence of pesticides in effluents happens in many parts of the world. It is has been documented that rivers in Brazil, Spain, China, India, and Pakistan present similar findings, including the risk estimates in nearby populations, which has driven the development of common methodological frameworks for the assessment of risks of these and others pollutants, in order to prioritize mitigation actions (López-Benítez et al., 2024;).

Our research would not be possible without collaboration between Mexican institutions and foreign universities, particularly in Canada, which reflects the central role of the internationalization of higher education. In our project, we have a long trajectory of joint projects with doctor Harvey Shear, emeritus retired professor at Toronto University-Mississauga, with whom we have been working since the year 2000. Alliances allow us to exchange methodologies, train researchers in real contexts, and develop joint projects that strengthen local scientific capacities. In addition, they favor global cooperation aimed at solving complex environmental problems, connecting the knowledge generated in Jalisco with international networks and contributing to a more comprehensive, critical education committed to sustainability.

WHAT CAN BE DONE AFTER DIAGNOSIS?
The identification of the problem is only the first link in the chain. Scientific studies propose the need to implement comprehensive strategies, where different elements converge: systematic monitoring of pesticides in water, sediments, and biota located nearby agricultural areas (Sumudumali & Jayawardana, 2021); regulation and control of the use of pesticides, including the complete elimination of highly hazardous compounds highlighted in international conventions (Fagundes et al., 2025); protection of riverside populations that are the most affected through health campaigns, outreach workshops, and community approaches to explain the silent danger of pesticides and strengthen environmental education; implementation of remediation technologies such as wetlands and wastewater treatment, that have proved potential for reducing agricultural pollutants (Kuhn et al., 2022; Nan et al., 2023). Finally, integrated waterhed management, articulated with the political entities involved, authorities, civil society, and academia, is key to treating this problem that affects public health. International experiences have shown that sustained coordination of the above approaches can reduce river pollution.

CONCLUSIONS
The Santiago River is a living example of how the benefits of modern agriculture can be overshadowed by environmental and health impacts if there is no articulation between academia and public institutions. The presence of pesticides in rivers represents a global public health problem that must be addressed as soon as possible. It is urgent to strengthen environmental surveillance and reinforce educational programs and informative talks in vulnerable communities to minimize the long-term impact of these pollutants. At the same time, this work reaffirms the importance of national and international collaboration to address complex environmental problems that transcend borders. When articulated with public policies and social participation, science can become a powerful tool to protect water and the health of present and future generations. Taking care of our rivers is not just a technical task: it is an ethical commitment to the collective well-being of the environment and society.

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