Raquel Cela Dablanca: «Understanding how antibiotics interact with soil is key to protecting environmental health»

Raquel Cela Dablanca, a researcher at the Sustainable Environmental and Forest Management Unit (UXAFORES) at Campus Terra, has just defended her doctoral thesis with the highest qualification, addressing one of today's major environmental challenges: the presence and behavior of antibiotics in soils.

Her work focuses on how these emerging pollutants, mainly from human and livestock activity, interact with agricultural soils and what risks they may pose to ecosystems and public health.

Throughout this interview, Raquel explains the main contributions of this pioneering research in Galicia, from the study of the capacity of soils to retain antibiotics to the analysis of their mobility, degradation, and possible entry into the food chain.

She also reflects on the priority research lines for the coming years, the roles of microorganisms and resistance genes, and the potential of low-cost waste materials as tools for mitigating environmental pollution.

-Your doctoral thesis, recently defended with the highest grade, addresses the presence and dynamics of antibiotics in different types of soils. What gaps in knowledge were you seeking to fill, and what do you consider to be the main contributions of the thesis?

-Several research studies indicate that our bodies absorb a very low amount of the administered dose, with up to 90% of what is ingested being excreted in feces and urine.

This thesis sought, first of all, to assess the current situation in Galicia regarding the presence of antibiotics for human consumption in different environmental compartments (WWTP sludge, sludge previously treated by waste managers, soils amended with this sludge, and the vegetation that grew in these soils) with the aim of determining whether their presence could pose any risk.

In addition, the aim was to investigate the extent to which Galician soils can adsorb these antibiotics, thereby retaining them and preventing their passage into water or absorption by plants and thus their entry into the food chain, which could pose a risk to human and environmental health.

When this research began, there were studies in other parts of the world on the capacity of various soils to retain these antibiotics, but none had been conducted with Galician soils.

-The presence of antibiotics in agricultural soils is a matter of concern both for its environmental impact and its relationship with antimicrobial resistance. In your experience, what lines of research should be prioritized in the coming years?

-In the coming years, it would be advisable to continue researching the interaction of antibiotics with soils, working with other antibiotics, as well as with a wider variety of soils, since there are soils with very different physicochemical properties, which significantly condition the behavior of antibiotics.

In Galicia, for example, we have soils with a high organic matter content, which gives them a high adsorption capacity; however, this is not the case in other parts of Spain, where organic matter percentages are significantly lower.

In addition, I consider it essential to continue researching strategies to mitigate the impact of these pollutants on the environment, such as implementing treatments or measures to eliminate them in wastewater treatment plants (WWTPs).

At the microbial level, I consider it important to better understand how antibiotics alter the structure and function of soil microbial communities, the nutrient cycle, and plant health.

Another line of great interest would be to investigate antibiotic resistance genes and their dynamics: abundance, mobility, and factors that favor their spread in agricultural soils, especially when slurry is applied. I also consider it relevant to study the absorption of resistance genes by crops and their possible transfer to animals and humans.

-The Sustainable Environmental and Forest Management Unit (UXAFORES) develops a wide range of research lines. How does your work on emerging contaminants fit into the group's scientific priorities?

-One of the research lines developed by the UXAFORES group is “Soils: nutrition, contamination, and rehabilitation.” Within this line, there are different sub-lines, including “Soil contamination by heavy metals and emerging pollutants. Restoration and decontamination of soils and water.”

This is the subject of my thesis, which addresses soil contamination by antibiotics, considered emerging pollutants.

In addition, strategies to mitigate the harmful effects of these compounds on the environment are also being studied, such as the use of waste materials as possible decontaminants, with the recovery of these materials being one of the group's strategic lines of research.

-You have participated in competitive projects focused on ionophore antibiotics and human-made pollutants applied through sewage sludge. What specific differences and challenges does researching each of these types of compounds present?

-The differences and challenges of researching ionophore antibiotics versus those for human consumption are significant, as each group of compounds exhibits different environmental behaviors that may pose different risks.

Ionophore antibiotics are used to treat coccidiosis, a parasitic disease that affects livestock, so they come mainly from intensive livestock farming and reach the soil through the application of slurry or manure, unlike antibiotics for human consumption, which reach the soil through the application of sludge resulting from wastewater treatment.

In addition, their behavior in the soil is different. For example, ionophores tend to be adsorbed in large quantities, mainly due to their high hydrophobicity, while antibiotics for human consumption exhibit more diverse behaviors.

Some of them remain practically retained in the soil, while others show greater mobility. It should also be noted that ionophore antibiotics are for animal use only, as they are highly toxic to humans.

-Much of your scientific work focuses on the processes of adsorption, transport, mobility, and degradation of antibiotics. What experimental and analytical methodologies do you consider most decisive for advancing in this field?

-Adsorption is the methodology I focused on most during my pre-doctoral studies; this is one of the most important processes for explaining the fate of antibiotics and their behavior in the environment.

These reactions condition their transport, since the more the antibiotic is adsorbed, especially irreversibly, the more limited its mobility in the soil will be, reducing the probability of it reaching surface, subsurface, or groundwater, as well as its availability for absorption by plants or microorganisms.

Therefore, the interactions of antibiotics with soil play an important role in their presence or absence in water and their entry into the food chain.

The methodology used primarily involved batch experiments, in which solutions of increasing antibiotic concentration were added to a fixed amount of soil and/or bioadsorbent. These were left to stir for 48 hours and then centrifuged.

The resulting supernatants were filtered through syringe filters, and the antibiotic concentration was determined by HPLC-UV.

-You have also published on the use of bioadsorbents and low-cost materials for the retention or elimination of antibiotics. What practical potential do you see in these solutions, and what barriers exist to their application on a real scale?

-In this thesis, we focus on studying the capacity of various wastes or by-products from the forestry and canning industries, both of which are very active in Galicia, to adsorb several of the antibiotics most commonly used in human medicine.

Specifically, we worked with biomass combustion ash, pine bark and needles, mussel shells, and eucalyptus leaves, all of which are low-cost, widely available materials in our region.

These materials could be used, for example, in water decontamination processes at wastewater treatment plants, by placing them in containers through which contaminated water is passed.

In addition, this thesis demonstrated that adding some of these materials to soils generally increased their adsorption capacity. Therefore, we believe that this project can be scaled up to real-world conditions.

-Your research experience includes stays at Kingston University London and the Biological Mission of Galicia. What impact have these stays had on your training and the development of your thesis?

-Both stays allowed me to gain experience working in other groups and learn about studies that were not carried out in our laboratory, as well as different working methodologies.

I also had the opportunity to learn how to use new laboratory equipment and computer programs, which helped to broaden and complete my training. In addition, these stays also allowed me to meet new colleagues and establish relationships that could lead to future collaborations.

-After completing your PhD, what future prospects would you like to explore in academia or research? What questions remain open, and would you like to address in the next stage of your career?

-Once I have completed my PhD, I would like to continue researching topics related to emerging pollutants, such as other types of drugs, cosmetics, or pesticides, as I consider this to be a very interesting and important topic for the environment and public health, in which there is still much to research and work on.

However, I would also like to be able to work and conduct research in other areas that would allow me to complete my training and expand my knowledge, always in relation to soil, a fundamental element that often does not receive the attention it deserves.