Sustainable IL-DLLME-ETAAS for Ultra-Trace Lead Analysis in the Mar Menor Lagoon

The Mar Menor, Europe’s largest coastal lagoon, faces severe ecological deterioration driven by nutrient loading, limited water renewal, and persistent contamination linked to mining residues from the Cartagena–La Unión district. Lead (Pb) levels remain an indicator of potential contamination caused by runoff from nearby abandoned mining operations and subsequent accumulation in marine organisms. This one-year study monitored total dissolved lead across eight representative locations using a rapid, simple analytical procedure combining ionic liquid dispersive liquid–liquid microextraction (IL-DLLME) and electrothermal atomic absorption spectrometry (ETAAS). The IL-DLLME system, based on in situ formation of the ionic liquid and APDC complexation, enabled highly efficient preconcentration, allowing the determination of ultra-trace Pb levels using low-cost instrumentation, achieving detection limits unattainable with previous monitoring techniques. Measured Pb concentrations ranged from 0.325 to 0.765 µg L−1, showing low temporal variability but marked spatial heterogeneity, with elevated values in confined or anthropogenically influenced areas. The one-way ANOVA test confirmed significant spatial differences (p < 0.001), indicating persistent localized inputs and limited dispersion. These results highlight the chronic influence of historical mining and demonstrate IL-DLLME-ETAAS as a sensitive, sustainable analytical alternative for ultra-trace metal monitoring. Continued surveillance is essential to evaluate ecological risks and guide restoration efforts.