For much of the 20th century, soil was invisible to environmental regulation. It was considered capable of absorbing, diluting, or inactivating pollutants without any consequences. From the 1980s onward, this view began to change, and soil came to be understood as a living system that accumulates pollutants and can transfer them to plants, aquifers, animals, and ultimately, people. Nowadays, there is no doubt that soil pollution is an environmental and public health challenge, to the point that legislation already requires the removal of pollutants dumped decades ago or, if that is not possible, at least the neutralization of their mobility and toxicity.
With this change of perspective, a key question emerged: how can we know to what extent a soil is contaminated and whether cleanup measures are really working? The answer lies, among other things, in observing small species that live in the soil and act as indicators of its health, such as a type of arthropod known as a springtail, mites, or a group of earthworms called enchytraeids. These findings have had a direct impact on how Europe regulates pollution today, and throughout this process, CREAF’s research has played a key role.
A cross-country race
CREAF researcher Xavier Domene’s career is closely linked to the study of these issues within the framework of ecotoxicology. It began in 2003 with a doctorate in this field, after which he started collaborating with international groups with a common goal: to develop new standard methodologies and new model species to determine how toxic a substance is and what effects it could have on the entire edaphic (soil) ecosystem.
At the beginning of the 2000s, there were still only a small number of standardized biological tests-also called ecotoxicological tests- that made it possible to measure the real effects of pollutants on soil, and even fewer for complex contaminated waste.
Xavier Domene
This meant that many risk assessments were based solely on chemical analyses, “an insufficient method that did not reflect the real effects on the environment,” explains Domene. To fill this gap, after years of research and international collaboration, the research community succeeded in expanding and improving the set of standardized ecotoxicological tests.
Springtails, mites, and other organisms for measuring soil health
One of the key milestones at CREAF in developing these new ecotoxicological tests was research on soil fauna, especially springtails, but also mites and enchytraeids—tiny organisms that often do not exceed a millimeter in length. Despite their small size, they live in direct contact with the soil and react quickly to the presence of heavy metals, pesticides, industrial waste, or other toxic substances. They are so sensitive that their ability to survive and reproduce is affected even at very low concentrations of pollutants. “This makes them particularly useful biological indicators,” explains Domene.
Furthermore, these organisms are part of a complex network of relationships with other living beings in the soil, from those that feed on microorganisms to their predators. This connection makes them true sentinels of the ecosystem, “because if they are affected by pollution, we know that it will also affect other key species in the food web,” adds Domene.
Xavier Domene, CREAF researcher, Cornell University (Ithaca, NY, USA) 2010.
Photo of springtails that were used to make the final count of individuals (adults and juveniles) at the end of the OECD 232 ecotoxicological test.
Ecotoxicology soil samples
To standardize an ecotoxicological test, the team also had to demonstrate that both the indicator species and the methodology were reliable. This was done through so-called ring tests, or interlaboratory tests, in which centers in many countries apply the same protocol to verify whether they obtain consistent results. The species studied successfully passed these tests and were established as some of the most reliable indicators of soil health. For example, these tests make it possible to assess the risk of a contaminant before it reaches the market or to check whether land decontamination processes are producing good results.
From the laboratory to regulations
But the story does not end there. Once these methods were published in scientific reports and articles, they became the basis for standard tests developed by institutions such as the OECD and ISO. This step facilitated their incorporation into European legislation. In particular, the use of springtails of the genus Folsomia as a bioindicator of soil contamination, following a ring test with laboratories from the European Union, Canada, and the United States, contributed to the development of the OECD 232 method in 2009, an international protocol for soil ecotoxicology.
This method was later integrated, along with other tests involving soil species, into the European standard EN 14735:2021, which makes it possible to determine whether waste is ecotoxic and “is used both in Europe and in other countries such as Uruguay and Colombia,” adds Domene. Furthermore, in 2020, following another international ring test, a test based on the oribatid mite Oppia nitens (EN ISO 23266:2021) was standardized. “It has not yet been officially included in legislation because it is relatively new, but it has great potential,” highlights Domene.
The use of these standards is very broad. Thanks to these tools, legal limits can be established for pollutants or waste before they are commercialized. In addition to serving regulatory purposes, these standards also help evaluate the effectiveness of decontamination processes.
This trajectory shows a different way for research to impact society than more common approaches, as it is not based so much on direct interaction with political or social actors, but rather on generating solid and relevant scientific and technical knowledge that is ultimately integrated into technical standards and, finally, into legislation.
Anabel Sánchez, responsible for CREAF's impact area
Although these standards are already well established, according to Domene, soil ecotoxicology now faces new challenges. One of the main ones is evaluating the combined effects of different pollutants present simultaneously, which can intensify the toxic effects they have individually. In addition, materials such as bioplastics need to be studied because, despite being presented as more sustainable alternatives in terms of biodegradation, they still require proof that they do not have toxic effects on ecosystems. “We must be able to measure the impact on nature before starting to use them on a massive scale, and bioassays will play a key role in this objective,” he concludes.
References
