Tracing acid mine drainage from an accidental spill on the Estuary of Huelva (SW Spain)

Abstract

The Estuary of Huelva in southwestern Spain is severely impacted by acid mine drainage (AMD), primarily due to extensive mining activities in the Iberian Pyrite Belt (IPB), and to a lesser extent by industrial sources. The AMD has led to significant contamination of the Odiel and Tinto rivers, which carry high loads of metals into the estuary. In May 2017, an accidental spill occurred at La Zarza mine, releasing approximately 270,000 m3 of acidic water contained in a pit lake. This event increased the contamination levels in the Odiel River and subsequently in the Estuary of Huelva and the Atlantic Ocean. The current focus of our investigation is to understand the geochemical behavior of contaminants during estuarine mixing and evaluate the environmental impact of the spill, from the river to the littoral. Key findings include the chronic exposure of the estuary to mining pollutants, with specific contaminants escaping retention processes and altering the metal background levels in the Gulf of Cádiz. This study highlights the need for effective control measures in historical abandoned mining districts worldwide to prevent similar environmental disasters in the future.