Reviewed by Frances BriggsOct 14 2025
Spain's Mar Menor in Murcia still stores toxic metals from past mining, with levels higher than toxicity thresholds and values documented for comparable coastal ecosystems around the world.
Image Credit:tokar/Shutterstock.com
Published in Marine Pollution Bulletin, the study reconstructs the history of metal contamination in the 20th and 21st centuries and finds that the primary cause of metal accumulation in the sediments was the mining industry of the Cartagena-La Unión mountain range, which operated from the late 19th century to the mid-20th century.
Even after the mines were closed in the 1990s, metal flows still impacted the lagoon during rainstorm events, and the largest concentrations are now found in the southern part of the lagoon, nearer the old mining deposits.
Historical data show that maximum concentrations were reached in the mid-twentieth century, and while some decreased after mining discharges were banned in 1955, other metals continued to enter the lagoon via runoff carrying mining waste and new urban sources, such as wastewater and specialty boat paints.
The sediments of the Mar Menor contain thousands of tons of metals, including an estimated 9,100 tons of lead, 10,000 tons of zinc, and 450 tons of arsenic, with numbers demonstrating the scope of this past contamination.
The impact of these accumulations of metals, which at the moment are not affecting living organisms, could become greater in the future due to interactions with other pressures derived from human activities.
Irene Alorda, Researcher, Department of Physics, Autonomous University of Barcelona
The study cautions that even though surface concentrations are currently lower than they were for a large portion of the 20th century, eutrophication episodes, climate change, and bottom sediment resuspension could cause these metals to be released from sediments again, increasing their availability to aquatic organisms and endangering the biodiversity of the ecosystem.
Given that past impacts and the implications of global change might exacerbate current pollution, this study emphasizes the significance of managing coastal ecosystems in an integrated way. It also offers important data for organizing future pollution control and conservation plans for the Mar Menor lagoon and other ecosystems of a similar nature across the world.
Journal Reference:
Alorda-Montiel, I. et.al. (2025) A century of sediment metal contamination of Mar Menor, Europe's largest saltwater lagoon. Marine Pollution Bulletin. doi.org/10.1016/j.marpolbul.2025.118347.