Copper Complexing Capacity of Atmospheric Inputs: Methodological Approach and Short-Term Coastal Study

The organic complexation of Cu2+ in aquatic systems dominates its chemical speciation, affecting its reactivity and bioavailability. Using voltammetry, we investigated Cu2+ organic complexing capacity (CuCC) in atmospheric samples, including water-soluble aerosol fraction, rainwater (wet-only deposition), and bulk deposition (wet and dry deposition), collected in a coastal marine area (National Park Brijuni, Adriatic Sea). The focus was on minimizing analytical interferences from surface-active substances (SAS) that accounted for up to 56% of dissolved organic carbon. Method optimization was performed using model SAS (humic-like substances, fulvic acid, and pollen-derived organic material), resulting in an optimal desorption potential of −1.4 V and the addition of 1 mg/L Triton X-100. Under these conditions, CuCC parameters of average ligand concentration and conditional stability constant of (209.8 ± 6.7) nM and log K = (10.2 ± 0.6) in water-soluble aerosol fraction, (117.1 ± 5.0) nM and log K = (9.6 ± 0.2) in rainwater, and (142.9 ± 4.1) nM and log K = (10.2 ± 0.2) in bulk deposition were determined. Atmospheric inputs represented a source of weak Cu-binding ligands for marine areas. In conclusion, short-term monitoring provided insight into the variability of different atmospheric inputs and offered a methodological basis for future long-term, more comprehensive studies.