Links between size fractionation, chemical speciation of dissolved copper and chemical speciation of dissolved organic matter in the Loire estuary

In the Loire estuary, dissolved copper concentrations exhibit non-conservative behavior, with significant fluctuations linked to colloidal dynamics and organic matter interactions. Upstream of the tidal front (salinity S = 0.1), copper levels reach 80 nmol kg−1, likely due to agricultural runoff from vineyards, before dropping sharply at early mixing stages (S ~ 0.5) and rising again in low-salinity zones (S = 4.7). The study reveals that while humic substances dominate the complexing capacity of copper ligands (LCu), accounting for up to 95% in continental shelf samples, additional ligand classes—such as thiol-like and proteinaceous components—emerge in the inner estuary, potentially sourced from wastewater treatment plants. These findings highlight the critical role of dissolved organic matter (DOM) in mitigating copper toxicity by keeping cupric ion activity below harmful levels for phytoplankton, while also identifying anthropogenic inputs that alter copper speciation dynamics.

Dulaquais, G., Waeles, M., Breitenstein, J., Knoery, J., & Riso, R. (2020). Links between size fractionation, chemical speciation of dissolved copper and chemical speciation of dissolved organic matter in the Loire estuary. Environmental Chemistry, 17(5), 385–399. https://doi.org/10.1071/en19137