A Subterranean Mercury River Found in Mar Menor: An Invisible Threat to the Lagoon.

According to ТСН: In the Mar Menor lagoon in southeastern Spain, scientists have discovered a hidden source of toxic contamination — a subterranean river of groundwater containing mercury. The research showed that this invisible flow adds about one kilogram of mercury to the water body each year, creating an additional burden for an ecosystem that is already experiencing a prolonged crisis.

The project was led by Dr. Céline Laverny from the Institute of Marine Sciences in Barcelona. The team studied how traces of heavy metals migrate in coastal waters and their impact on the environment and local communities. Mar Menor is the largest coastal lagoon in the western Mediterranean region, which has long suffered from pollution. New data indicate that part of the toxic emissions comes from old mercury deposits left in the soil as a result of mining activities and intensive agriculture.

High Concentrations of Mercury

Researchers tracked a network of underground discharges coming from aquifers beneath the lagoon's bottom. The mercury level in this flow exceeds the readings recorded in the Albujón River, the main freshwater source in the region, by seventy times. When groundwater mixes with the lagoon's saline water, conditions are created for the formation of methylmercury — a highly toxic form of the element that accumulates in organisms and enters food chains. For this reason, the researchers identified these areas as potential "hot spots" for methylmercury formation.

A Threat to the Ecosystem

Currently, the level of mercury in the water and fish of Mar Menor is not critical, but scientists warn that an increase in methylmercury levels could change the situation. The lagoon has been suffering from algal blooms and a sharp decrease in oxygen levels for many years, leading to mass fish deaths. Warm summers and rising temperatures create favorable conditions for more active mercury transformation.

During the research, specialists collected samples of water, sediments, and groundwater wells, as well as analyzed radioisotopes that determine the rate of groundwater inflow to the lagoon. Calculations showed that the main source of mercury is the recirculation of lagoon water through sediments, while freshwater groundwater contributes a smaller share.

A Global Pollution Problem

Similar processes, according to research data from the USA, Asia, and Northern Europe, may also characterize other coastal areas of the world. The underground transport of mercury sometimes equals or even exceeds the volumes of pollution that enter from rivers. However, until now, the role of such flows in coastal lagoons has remained poorly studied.

This discovery underscores a global problem: toxic substances continue to enter the environment even after industrial sites are closed. The Minamata Convention obliges countries to control emissions but does not take into account old pollutants that remain in sediments and are moved by groundwater.

Scientists emphasize that the areas around Mar Menor require systematic monitoring of groundwater, cleaning of old deposits, and reducing the inflow of nutrients from agricultural lands to avoid further ecological crises. Identifying areas where groundwater surfaces can help the region develop effective strategies to restore the lagoon and reduce risks for marine life and local communities.

Water salinity and pollution in the Mar Menor lagoon threaten not only the ecosystem of the region but also the health of local residents and marine biological resources. As ecological problems become increasingly serious, it is crucial for governments and relevant organizations to focus on addressing this critical situation, considering not only the current but also the historical legacy of pollution. Implementing effective environmental protection measures will be key to improving the situation in this unique and vulnerable ecosystem.