Antimony Content and Speciation in the Water Column and Interstitial Waters of Saanich Inlet

Abstract

A hydride generation method was developed for the determination of Sb(III), Sb(III)-S and Sb(V) species in natural waters, and has been applied to the waters and interstitial waters of Saanich Inlet. In the oxic waters, dissolved antimony exists primarily as Sb(V) (1.2–1.4 nM) with a few percent Sb(III) (.01–.07 nM). Sb(III) production occurs in the photic zone and probably accounts for its concentration at levels greater than those predicted from equilibrium considerations. Even in the low H₂S bottom waters, there is no significant reduction of Sb(V) and Sb(III). However, up to 0.15 nM Sb(III)-S species is found there. In the upper 10 cm of the reducing interstitial waters there is a very large release of Sb from the particulate matter. At least 50% of the Sb exists as Sb(III) + Sb(III)-S. The remainder most probably exists as a thioantimonate. This dissolved Sb diffuses to the overlying waters where it is rapidly oxidized to Sb(V). In the deeper portions of the sediment, Sb is resedimented perhaps as a sulfide or associated with iron sulfide precipitation.

Dimethylstibonic acid occurs at low concentrations (.01–.03 nM) in the water column. In the methane zone of the pore waters, there is a significant production of methylstibonic acid reaching levels of up to 4.9 nM.