Jp. Gustafsson et G. Jacks, ARSENIC GEOCHEMISTRY IN FORESTED SOIL PROFILES AS REVEALED BY SOLID-PHASE STUDIES, Applied geochemistry, 10(3), 1995, pp. 307-315
Arsenic concentrations in soils may be elevated either because of anth
ropogenic activity or because of a high natural abundance of the paren
t material. In the unsaturated zone of seven forest soils in northern
Sweden, inorganic As(V) generally dominated the solid-phase speciation
while non-NaBH4-reducible organic As associated with isolated humic s
ubstances (humic As) was present in low amounts. In unpolluted soils,
absorbed As(V) was more or less constant through the B and C horizons
and did not show any obvious relationship with secondary short-range o
rdered Fe or Al minerals-this suggested that most As(V) had formed ear
ly during pedogenesis asa result of sulphide weathering. When a small
amount of As(V) was added to the mineral soils, adsorption was almost
complete and the amount of remaining As(V) in solution depended on the
ratio of pyrophosphate-C to oxalate-(Fe + Al). On higher As(V) additi
ons, the amount of adsorption sites governed the As solubility. As reg
ards the humic As, the XAD-4 acid fulvates were more enriched with As
as compared to the hydrophobic acids. The As content of the forest Boo
r was highly dependent on the distance from the Ronnskarsverken non-fe
rrous metal smelter, but did not reflect the As content of the underly
ing horizons; thus, biological uptake of As from the mineral soil appe
ared to be very low.