Industrial pollutants discovered for the first time in Mediterranean corals

Pollutants from the burning of fossil fuels have been discovered in corals for the first time, giving scientists a potential new tool to track the history of pollution, according to a new study led by UCL researchers.

The study, published in the journal Total Environmental Science, identified carbon particles emitted by the combustion of fossil fuels embedded in corals in Illa Grossa Bay, off the Columbretes Islands in the Mediterranean Sea. The discovery of this type of pollution – known as fly ash or spheroidal carbonaceous particles (SCP) – contaminating natural deposits is considered an indicator of the presence of human influence on the environment and a historical marker of the beginning of the proposed Anthropocene era.

Corals are a commonly used natural archive for paleoclimatic studies due to their measurable growth rates. Similar to tree rings, their long lifespan and slow, steady growth can provide scientists with annual, monthly, or even weekly environmental data going back several years.

Until now, they have been widely used to assess past climatic conditions, such as water temperature and chemical composition, but this is the first time that polluting particles, other than microplastics, have been recovered in corals.

Lead author Dr Lucy Roberts (UCL Geography) said: “The discovery of these pollutants embedded in coral skeletons spans decades and paints a clear picture of the scale of human influence on the environment. able to see this type of contaminant in corals, and its appearance in these deposits parallels the historical rate of fossil fuel burning in the region.

Corals, which are small invertebrates that tend to live in expansive colonies, ingest SCP pollutants from surrounding waters, incorporating them as they develop their calcium carbonate skeleton.

Researchers from the Instituto de Acuicultura de Torre de la Sal (IATS-CSIC) collected coral samples from several sites along a reef off the coast of Castelló, Spain. The coral species Cladocora caespitosa has been studied and monitored there for two decades and the place is considered a sentinel site of global change.

The corals are located almost 60 kilometers from the shore and in a protected marine reserve, thus minimizing the risk of local contamination. The species is the only Mediterranean coral capable of forming large reefs and is known to grow at an average of around 0.3 centimeters per year.

Once in the UCL laboratory, the corals were dissolved in acid, leaving behind any polluting particles embedded in the skeleton. The team first counted all the SCPs present in the remains under a microscope. The samples were then observed under an electron microscope and analyzed using X-rays to look for chemical signatures of SCP contamination indicative of coal or oil-fired power plants.

The team found that corals showed a significant increase in SCP contamination between approximately 1969 and 1992. This corresponds to a time when Europe was rapidly industrializing and coal consumption in the country was increasing significantly.

These results are consistent with other measurements of SCP contamination taken in mountain lakes in Spain, supporting the idea that corals can serve as a natural archive to assess changes in pollution levels over time. .

These discoveries come at a time when scientists are searching for tools to mark the beginning of the Anthropocene era, a unit of geologic time, used to describe the most recent era in Earth’s history where human activity is become the dominant influence on the planet’s climate and environment. .

A number of scientists have advocated using the presence of SCPs as a marker for the start of the Anthropocene, and their discovery in coral skeletons supports this argument. They have previously been identified in lake and marine sediments, ice cores and peat beds.

Dr Roberts said: “As it becomes clearer that humans have altered the natural environment to an unprecedented level, these pollutants act as indelible markers, signaling the start of the Anthropocene era. This is valuable for researchers trying to better understand human history. impact on the natural world and is a powerful reminder of the extent of human influence on the environment.

This research was carried out by UCL, in collaboration with the Instituto de Acuicultura de Torre de la Sal, Spain and the University of Leicester.