Antimony in the Lot-Garonne river system: a 14-year record of solid-liquid partitioning and fluxes

Knowledge of the environmental chemistry of antimony (Sb) in aquatic systems is limited, and a better understanding of its geochemical behaviour is needed. Based on a fourteen-year survey (2003-2016) with monthly measurements of dissolved and particulate Sb at five sites in the Lot-Garonne river system, combined with daily measurements of water discharge and suspended particulate matter, this work characterises Sb behaviour in the upstream major river watershed of the Gironde Estuary. The survey provides a first regional geochemical Sb background in the Garonne River watershed for dissolved (similar to 0.2 mu g L-1) and Th-normalised particulate Sb (Sb-p/Th-p similar to 0.25) concentrations. Observed decreasing temporal trends (<1 ng L-1 in dissolved and <0.02 mg kg(-1) in particulate concentrations per month) at sites representing natural concentrations probably reflect global atmospheric Sb dynamics at the watershed scale. Regular seasonal cycles of solid/liquid partitioning, with higher solubility in summer (matching high dissolved and low particulate concentrations), reflect water-discharge and suspended particulate matter transport dynamics and possibly seasonal (bio)geochemical processes. Furthermore, this coefficient decreases from the river to the estuarine reaches (from average log(10)K(d)4.3 to minimum 3.7 L kg(-1)), suggesting an increased solubility of Sb in estuarine systems. Flux estimates indicate the relevance of the dissolved fraction in Sb transport (with negligible influence of the colloidal fraction) and a total flux (dissolved + particulate) entering the Gironde Estuary of 5.66 +/- 2.96 t year(-1) (similar to 50 % particulate). These results highlight the importance of timescales and environmental parameters for understanding and prediction of future Sb biogeochemistry.