Photodissolution of copper from resuspended coastal marine sediments

Abstract

Total dissolved Cu (TDCu) was photoproduced from suspensions of estuarine and coastal marine sediments from varied biogeochemical settings after exposure to the equivalent of 1 day of sunlight. Net photorelease (defined as the difference between mean light and dark concentrations) of TDCu occurred in 10 of 13 experiments and ranged from 1.1 nM to 11.8 nM (0.88–46.1 nmol Cu g −1 dry sediment). Photorelease was observed over environmentally relevant total suspended sediment concentrations ranging from 38 mg L −1 to 460 mg L −1 . The magnitude of photorelease was directly correlated to the 1 M HCl‐extractable Cu and Fe contents of sediments. Photoreleased Cu was likely associated with organic matter and/or Fe oxyhydroxides, both of which are photoreactive. Photoreleased TDCu persisted for at least 24 h after irradiation indicating that the Cu was not immediately scavenged back onto particles, most likely because it was stabilized by complexation with dissolved organic matter. Results of this study are important because a conservative estimate of the areal flux of TDCu from irradiation of a modest suspended sediment loading of 100 mg L −1 in the top 100 cm of a sunlit water column would be 460 nmol m −2 d −1 , which is comparable to or significantly larger than benthic and riverine fluxes of the metal in estuarine and coastal environments. These results suggest that photolytic fluxes are a significant yet previously unrecognized source of bioactive Cu to natural waters.

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