In late February 2025, a train carrying benzene derailed in Hustopeče nad Bečvou, and within hours, a race was on to save the groundwater and surface water. One of the most toxic industrial substances began seeping into the gravel-sand subsoil. While fieldwork was underway to prevent the spread of contamination, decisions were already being made in the CXI TUL laboratories regarding how to subsequently clean up the contaminated rock environment.
The accident ranks among the most serious environmental incidents in the Czech Republic in recent years. After a tanker train derailed, hundreds of metric tons of benzene leaked; due to the highly permeable geological subsoil, it quickly seeped into deeper soil layers and into the groundwater. The combination of the substance’s high toxicity and local conditions complicated both the emergency response and the subsequent remediation. The key was to stop further spread, determine the extent of the contamination, and establish a remediation strategy for the entire site.
It was at this stage that CXI TUL became involved in the solution. At the request of the renowned remediation company DEKONTA, a.s., a team led by RNDr. Jan Němeček, Ph.D., began testing the feasibility of the in situ chemical oxidation (ISCO) method. This technology is designed to break down benzene directly within the rock matrix, without the need for extensive excavation of contaminated soil or the pumping out of large volumes of groundwater. The goal was simple: to find a method that would work quickly, safely, and under the actual conditions of the affected site.
Benzene Remediation: Technically Simple, Complicated in Practice
Benzene is a highly toxic and carcinogenic substance that rapidly penetrates into groundwater in permeable subsoil, where it dissolves and spreads further as the water flows toward surface water bodies. Benzene also binds to rock particles and migrates in the form of vapors into overlying unconsolidated layers.
Scientists in Liberec therefore tested in situ chemical oxidation (ISCO) technology under laboratory conditions. The goal was to find an oxidant capable of breaking down benzene directly underground into less hazardous substances.
The tests evaluated two main options: activated hydrogen peroxide and sodium peroxodisulfate. Both substances removed up to 99.99% of the benzene, but there was a difference in their kinetics and impacts on the natural environment. Activated hydrogen peroxide achieved nearly complete degradation of the contaminant within a single day. Activated sodium peroxodisulfate was slower and also significantly altered the chemistry of the water; it acidified the environment and increased the sulfate content in the water, which poses an additional environmental burden.
For field applications, the researchers therefore unequivocally recommended activated hydrogen peroxide.
Dosage Matters
It was not just the oxidant’s effectiveness that was key. It was equally important to determine how the chemical reaction would behave in a real geological environment. The team of scientists therefore also analyzed what is known as soil oxidant consumption (SOD). It turned out that a significant portion of the oxidizing agent does not react solely with benzene but is also consumed to a significant extent by the rock environment itself, particularly by natural organic substances present in the fine-grained fraction of the soil.
An oxidant consumption value was determined specifically for the local composition of the aquifers, which is essential for the correct dosing of chemicals in the field so that the remediation is not only effective but also economically viable and safe for surrounding ecosystems.
One Year After the Accident: Research Turns into Real-World Assistance
While the public often perceives university science as a distant world of laboratories and grant projects, it is precisely situations like this that demonstrate its practical impact. The results of the work by researchers at CXI TUL did not remain confined to academic studies but directly influenced decisions regarding the technology used to clean up one of the largest environmental accidents in recent years.