Assessment of Emerging Pollutants in Groundwater Resources of El Hierro and La Palma (Canary Islands): A Comparative Study

Emerging pollutants (EPs) are contaminants detected in water bodies that lack thorough prior investigation, resulting in limited regulatory frameworks for their control. This poses a significant threat to regions heavily reliant on groundwater for agriculture, drinking water, and other essential uses. The Canary Islands, particularly El Hierro and La Palma, serve as critical case studies due to their unique ecosystems and dependence on groundwater. El Hierro, designated as a UNESCO biosphere reserve in 2000, operates primarily on renewable energy, whereas La Palma exhibits diverse hydrological dynamics influenced by agricultural and urban activities.

A comprehensive analysis of 70 EPs was conducted at 19 sampling points in El Hierro and at 14 locations across La Palma, utilizing high-performance liquid chromatography-mass spectrometry (HPLC-MS). The study focused on five EP categories: ultraviolet (UV) filters, UV blockers/stabilizers, parabens, pharmaceutically active compounds (PhACs), and pesticides. In El Hierro, pesticide residues were absent; however, significant concentrations of UV filters, UV stabilizers, and PhACs were detected, with La Frontera municipality showing the highest contamination. In contrast, La Palma exhibited notable concentrations of PhACs and UV stabilizers, particularly in Breña Baja and wastewater treatment plants (WWTPs). Pesticides, including imidacloprid and acetamiprid, were detected at concerning levels in La Palma's groundwater.

Cluster analysis revealed spatial patterns of EP distribution, segmenting the islands into distinct zones based on pollutant concentrations. In El Hierro, four clusters were identified, with sampling depth correlating positively with EP levels, highlighting potential vertical contamination gradients. Similarly, La Palma showed three to five clusters delineating contamination hotspots, aiding in the identification of priority areas for remediation. These findings underscore the urgent need for preventive measures to mitigate EP entry into the water cycle from domestic, agricultural, and industrial sources, beyond traditional remediation approaches post-contamination.

Comparative analysis between the islands demonstrated shared contamination trends but also emphasized unique local factors influencing EP presence. This highlights the necessity of tailored management strategies to protect groundwater resources in these fragile environments. Future research should focus on elucidating the mechanisms driving high EP concentrations at various depths and assessing long-term impacts on ecosystem and human health.

This study advocates for comprehensive regulatory frameworks and proactive strategies to prevent EP contamination, ensuring the preservation of groundwater resources essential to the sustainability of the Canary Islands.