Speciation of aluminium, arsenic and molybdenum in excessively limed lakes.
The possible existence of the potentially toxic oxyanions of Al (Al(OH)(4)(-)), As (HAsO(4)(2-)), and Mo (MoO(4)(2-)) was examined in excessively limed lakes. In-situ dialysis (MWCO 1 kDa) was performed in the surface and bottom waters of two excessively limed lakes (pH 7.1-7.7) and one acidic lake (pH approximately 5.4). The dialysable metal concentrations were compared to the equilibrium distribution of species as calculated with the geochemical code Visual MINTEQ incorporating the CD-MUSIC and Stockholm Humic models for complexation onto colloidal ferrihydrite and dissolved organic matter. Arsenic and molybdenum in the excessively limed lakes were to a large extent present in the dialysable fraction (>79% and >92% respectively). They were calculated to exist as free or adsorbed oxyanions. Most of the Al was observed to reside in the colloidal fraction (51-82%). In agreement with this, model predictions indicated aluminium to be present mostly as colloids or bound to dissolved organic matter. Only a small fraction was modelled as Al(OH)(4)(-) ions. In most cases, modelled values were in agreement with the dialysis results. The free concentrations of the three oxyanions were mostly low compared to toxic levels.
Sjöstedt
Carin
C
Department of Land and Water Resources Engineering, KTH (Royal Institute of Technology), Teknikringen 76, SE-100 44 Stockholm, Sweden. carinsj@kth.se
Wällstedt
Teresia
T
Gustafsson
Jon Petter
JP
Borg
Hans
H
D000535:Aluminum / Q000032:analysis*; D001151:Arsenic / Q000032:analysis*; D008982:Molybdenum / Q000032:analysis*; D014874:Water Pollutants, Chemical / Q000032:analysis*
D014874:Water Pollutants, Chemical; D008982:Molybdenum; D000535:Aluminum; D001151:Arsenic