In Yucatán, two researchers developed an accessible method to determine if there is toxicity in water using onions. The model has attracted attention because it is less expensive and complicated than other tests. It has been replicated in other universities and a network for monitoring the entity's aquifer has been gradually formed.
The so-called “C-BOYA Project” emerged at the same time that the Covid-19 pandemic began. By then, the researchers from the Sisal Chemistry Unit of the Faculty of Chemistry of the National Autonomous University of Mexico (UNAM), Gabriela Rodríguez and Elsa Noreña, had 12 years of experience testing for contamination in water collected in different parts of the state, but they usually resorted to expensive and complicated methods.
For example, Dr. Rodríguez generally experimented with animals such as crustaceans and fish. And it was just then that the bioethical guidelines for carrying out scientific research changed, with the aim of minimizing the use of animals in experiments.
While trying to find a substitute to make her projects in accordance with bioethical provisions, the academic received an article from the Bulletin of Environmental Contamination and Toxicology, in which onions were used to learn about the effects of discharges from a textile industry.
It wasn't the black thread: according to the specialist, the first references to the use of onions in scientific experiments date back to 1930.
In addition, researchers from Guadalajara and Brazil recently worked with the vegetable and the Mexican Institute of Water Technology (IMTA) included a similar model in a compilation of bioassays. However, “everything was gray literature and for environmental issues,” said Dr. Noreña.
For this reason, they decided to design, with all scientific rigor, a bioassay to determine using onions if the water contains toxic agents. The opportunity came when the call for the UNAM Research and Technological Innovation Project Support Program (PAPIIT) opened in 2020 and they were selected.
As was the case in the midst of the health emergency, a good part of the first phase of the project was carried out at home. Patricia Guadarrama, from the Faculty of Sciences of the UNAM, gave them instructions to germinate onions and Loreni Cauich, a master's student who was part of the team, obtained batches of the vegetable and did tests in her own kitchen. Little by little they were putting together the protocol for the bioassay.
How to use an onion to know if the water is contaminated?
The first phase of the bioassay is simple. Broadly speaking, six onions are subjected to a conditioning process for 48 hours. After that period, half of the onions are placed in distilled water as a control group and the others are soaked in the sample for 24 hours. From here on, the process is complicated, since parts of the roots must be cut and preserved with chemicals, under specific circumstances.
Roots can be tested for genetic expression or can be examined under a microscope to detect genotoxicity, since many substances, such as herbicides, have the ability to alter deoxyribonucleic acid (DNA), or cell chromosomes.
The effects are observable in onions because when the roots are growing they are highly vulnerable and if exposed to any toxic substance, the damage is more evident. According to Rodríguez, when viewed under a microscope, the cell nucleus should occupy almost two-thirds of the size of the cell and look “like a pepperoni”: round. If it looks “like a raspberry” or there is a large core and several small ones (called micronuclei), something is wrong.
“Just having one micronucleus is bad, but some cells can have up to six. That's genetic material in pieces,” the specialist explained.
Onions should be soaked for an additional 48 hours. At the end of that deadline, the roots are measured again to check for markers related to oxidative stress: toxic substances interfere with the cellular process, so if there are contaminants in the samples, the roots will grow little or nothing.
For now, it is not possible to detect with the bioassay what are the toxic elements present in water or if they are harmful to people, but specialists do not rule out that these tests can be mixed with others to obtain more information.
“What is no turning back is that if the onion has nuclear anomalies, that water has potentially toxic substances at bioavailable concentrations for beings who are in contact with it. Maybe there are substances that are not toxic to humans, which are even in the products we buy, but perhaps they are toxic to other organisms that are also part of an ecosystem, and in the long run, they will also harm humans, for example, in the economic sector,” said Rodríguez and Noreña.
Photo: courtesy of C-BOYA Project
Towards a water monitoring network in Yucatán
With the support of students and academic staff from UNAM and other universities, the C-BOYA Project team has analyzed water collected in different parts of Yucatán and even from other entities in the country, with impressive results.
For example, the samples taken in a line of 15-meter-deep wells located on the road between the port of Sisal and its municipal seat, Hunucmán, came out clean. However, the Sisal shelter area showed 4% of nuclear anomalies, an indication that this liquid is not as clean.
They also studied samples from the Dos Bocas port, in Tabasco, which had between 8 and 10% of nuclear anomalies.
Until now, the most alarming level of pollution has been found in the Lerma River, located in the center of the country. In that case, the experiment was carried out with three samples: one from a wetland, and two from sites with both urban and industrial wastewater discharge. In the last few, they observed cells with up to six micronuclei. They reached 26% of nuclear anomalies.
“In that case it was very obvious, those samples helped us to make the album of genetic abnormalities,” Rodríguez recalled.
The accessibility of bioassay with onions has aroused the curiosity of students and specialists from different schools and universities. For example, last year, Dr. Juan Sandoval, from the Technological Institute of Tizimín, joined the work team in order to expand sampling areas.
In that municipality they did a test and the result was 26% of nuclear anomalies. However, the test was done only with one onion, so the analysis will be repeated with more vegetables and a control group.
The objective of the researchers is that more and more people and schools can replicate the bioassay to form a water monitoring network throughout the entity and monitor the quality of the Yucatan aquifer.
“Academia does analysis, but everything is published in international journals, generally in English, and most people don't have access to these reports. That's why it's important for us to make that link with the community, that more people and students get involved in water monitoring and scientific work,” said Noreña.
Photo: courtesy of C-BOYA Project
The specialists insisted that scientific dissemination, with accessible language and simple and low-cost processes, are crucial in the entity today, especially to protect water, since it faces more and more risks, as Causa Natura Media has documented.
“There is more and more development and more inhabitants. The levels of pollution seen elsewhere in the country have not yet been reached, but we know that there are many pollutants that can affect water quality. The intention of Project C-BOYA is to see how the aquifer is doing and to detect red spots that do deserve further study. And there is a part of the bioassay that communities can carry out,” said Noreña.
Academics are accepting all invitations to schools, forums and environmental conferences to present the bioassay in order to reach more people. They are currently working on a project to evaluate water quality in 20 cenotes and next year they will carry out well monitoring funded by National Geographic.
They are also designing prototypes with other vegetables, such as lettuce. They hope to begin the development of that project soon.
“Involving the community in monitoring the quality of the water they use or drink is very important, because then the people who participate become more concrete and begin to take care of it as well,” concluded Noreña.
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