On the Day of the Black Sea, the question of his health is particularly acute. A unique body of water with a rich history is facing serious environmental problems today. SFedU scientists and their colleagues from the Hydrochemical Institute of the Federal Service for Hydrometeorology and Environmental Monitoring studied the results of 18 years of observations to assess the scale and dynamics of oil pollution in coastal waters. Two major disasters have become the reason for close attention: the tanker wreck in the Kerch Strait in 2007 and in 2024.

From 2007 to 2025, researchers collected and analyzed 275 samples of seawater and 190 samples of oil clots and films from the coast of the Kerch Strait, Anapa and Novorossiysk regions. They used two methods: the classical infrared spectrophotometric method, which measures the content of predominantly aliphatic (the simplest) hydrocarbons, which are the most important class of substances in oil, and the more sensitive fluorimetric method, which effectively determines the content of hydrocarbons with a significant proportion of aromatic compounds in their composition.

The first of these is a classic method widely used in the Roshydromet network, which directly measures the concentration of predominantly aliphatic hydrocarbons (HC). The second is a more sensitive method that makes it possible to effectively determine the HC content with a significant proportion of arenes luminescent in ultraviolet light. The results of the study of oil aggregates and slicks are considered in the article and in this work are used only for comparative purposes.

The data showed significant fluctuations in the concentrations of petroleum hydrocarbons in the water. However, pollution peaks that were many times higher than normal were expected to be recorded immediately after the tanker crashes.

"High HC (hydrocarbon) concentrations, many times higher than the maximum permissible concentration, were expected to be recorded in areas of emergency fuel oil spills in the first weeks after shipwrecks (December 2007, January 2025), as well as during the two or three warm seasons following the disaster in 2007. This effect could have been caused by the summer activation of the destruction of fuel oil, numerous traces of which, despite the cleanup measures, remained on a number of hard—to-reach areas of the coast," said Andrey Kuznetsov, Director of the Institute of Earth Sciences of the Southern Federal University.

Curiously, after the 2024 disaster, there was no such summer spike in pollution in 2025. On the contrary, it has one of the lowest pollution levels in all 18 years of observations.

Scientists attribute this to several factors. Firstly, the cleanup work at the Anapa embankment in 2024-2025 was much more extensive than in the little-developed Kerch Strait in 2007-2008. Secondly, the difference in coastal landscapes played a role. The sand of the Anapa Embankment acted as an "anchor" and "filter", retaining clumps of fuel oil and preventing them from freely migrating back into the water, unlike the rocky shores of the Kerch Strait, where fuel oil remained on the surface for years.

"In general, it can be concluded that for the coastal waters of the northeastern coast of the Black Sea, which have been exposed to chronic oil pollution for many years, the accidental spills of fuel oil containing few water-soluble components in 2007 and 2024 did not lead to a sharp increase in HC concentrations compared to the background that has developed over two decades," noted Andrey Kuznetsov.

Nevertheless, the researchers warn that the preservation of sufficiently "fresh" fuel oil mixed with sand and lost buoyancy on the surface and underwater surfaces of beaches and in their thickness, as well as on the rocky surfaces of cliffs, breakwater terraces and coastal protection structures for the next two to three years poses a threat of secondary contamination of seawater with decay products.

The results of the analysis will be presented at the International Scientific Conference-School of Marine Geology "Geology of the Seas and Oceans", which will be held at the P. P. Shirshov Institute of Oceanology of the Russian Academy of Sciences (Moscow) on November 17-21, 2025, where issues of the ecology of the Black Sea and the consequences of the fuel oil spill will be discussed.

On Black Sea Day, SFedU scientists remind of the fragility of marine ecosystems and the need to continue systematic monitoring, especially in conditions of active shipping and oil production in the region.