The sargassum that reaches the coasts of the Mexican Caribbean every year not only represents a tourist and economic problem, but when it decomposes it releases a mixture of chemical compounds potentially dangerous for human health and coastal ecosystems.
This is revealed by a study carried out by the National Technological Institute of Mexico, the Center for Research and Advanced Studies of the National Polytechnic Institute (Cinvestav) and the Scientific Research Center of Yucatán.
The work, which analyzed the chemical composition of the leachate generated by this algae when it degrades, shows that it contains concentrations of hydrocarbons, metals and other substances that exceed the limits of Mexican and international safety standards, which poses risks for coastal communities and the environments where it is deposited.
In 2011, a large-scale accumulation of sargassum in the ocean spread across the Atlantic and caused massive gold tides off the west coast of Africa and in the Caribbean. In Mexico, the unusual arrival of sargassum began in 2014 and the first massive accumulations on beaches emerged in 2015.
During the busiest month, the equivalent of 337 dump trucks loaded with sargassum arrived for each kilometer of coastline. In 2019, at its critical point, arrivals were equivalent to half a million trucks. By 2025, the mass of sargassum accumulated in the tropics is estimated at almost 1.9 million dump trucks, almost double the 2018 record.
Although in the open sea sargassum fulfills a key ecological function by serving as shelter, food and reproduction area for fish, crustaceans and other marine species, when these large masses reach the coasts, the balance is broken: its accumulation and decomposition consume oxygen and release toxic compounds.
Sargassum, which also has the ability to absorb metals and metalloids such as arsenic, cadmium, chromium, nickel and zinc from the marine environment, can release these components during its decomposition.
For this research, scientists collected sargassum from the beaches of Akumal in the Riviera Maya. Once in the laboratory, the biomass was monitored for 80 days at room temperature, a period in which the leachate was generated and then analyzed using different methods to detect the presence of metals and hydrocarbons.
The results were conclusive: the concentrations detected exceed the limits established by NOM-001-Semarnat, which sets the maximum limits of contaminants that wastewater discharges can contain; Even according to the criteria of the United States Resource Conservation and Recovery Act, sargassum leachate should be considered a toxic waste, due to high concentrations of arsenic, a recognized carcinogen.
The research warns that the risk is worsened in the Yucatan Peninsula – where the flow of groundwater occurs through an extensive network of underground rivers – when sargassum removed from beaches is deposited in inappropriate sites, such as mangroves, forests or undeveloped land that lacks adequate infrastructure for the management and treatment of leachate.
“Given the high permeability of the karst substrate, characteristic of the Yucatan Peninsula, there is a significant probability that toxic elements will quickly infiltrate the aquifer, thus compromising the main source of fresh water in the region,” the study states.
In the work published in the scientific journal Marine Pollution Bulletinthe authors emphasize the urgency of comprehensively addressing the leachate generated by the large sargassum deposits in the Mexican Caribbean through the design and operation of final disposal sites with adequate infrastructure for its containment and treatment.