KINETIC CONTROLS ON METALLOID SPECIATION IN SEAWATER

Mechanisms for the production of thermodynamically unstable species of three metalloids, antimony, arsenic, and selenium, and the rates of their transformation to stable forms have been critically reviewed. The occurrence of thermodynamically unstable species of these metalloids falls into two categories: reduced species in oxic waters and oxidized species in anoxic water. In surface waters biotic processes produce reduced species (e.g. Sb(III), arsenite, selenite), while in deep anoxic waters lateral advection and sinking detritus deliver oxidized species (e.g. arsenate, antimonate) from surface waters. In both cases, slow rates of conversion allow unstable species to persist. Dissolved and particulate data for antimony, arsenic, and selenium speciation in the Black Sea are used to illustrate the processes involved in this kinetic stabilization.