Antimony mobility in lead smelter-polluted soils

Emissions from primary and secondary lead (Pb) smelters are responsible for high concentrations of metallic contaminants (Pb, Cd and Zn) in soils. However, less attention has been paid to volatile metalloids, such as antimony (Sb), which accompanies Pb smelting activities. This paper is focused on geochemistry of Sb in the forest and agricultural soils in the vicinity of the Příbram Pb smelter (Czech Republic), with emphasis on Sb distribution, chemical fractionation and comparison with the behaviour of another toxic metalloid, arsenic (As). Forest soils were enriched in Sb (4.86–2058 mg kg− 1, mean: 379 mg kg− 1, median: 155 mg kg− 1) with the highest concentrations in the organic horizons. Arsenic was found in significantly lower concentrations in forest soils (9.16–447 mg kg− 1, mean: 127 mg kg− 1, median: 82.9 mg kg− 1). High concentrations of metalloids in forest soils are related to higher interception of smelter emissions by tree canopies. The Sb/As concentrations ratios ranged between 4.6 and 16.4 in the organic soil horizons, which is in agreement with (i) higher Sb deposition between ∼ 1890 and the 1970s as recorded by 210-Pb dated peat cores from the vicinity of the smelter and (ii) rare historical analytical data on processed concentrates and dust from the smelter flue-gas cleaning system. In contrast to organic horizons of forest soils, the concentrations of the two metalloids are rather similar in agricultural soils and in mineral horizons of the forest soils. Antimony concentrations in agricultural soils were in the range 3.12–131 mg kg− 1 (mean: 39.3 mg kg− 1, median: 23.8 mg kg− 1), whereas As concentrations were in the range 4.33–154 mg kg− 1 (mean: 60.3 mg kg− 1, median: 42.5 mg kg− 1). Factor analysis showed that Sb and As are statistically correlated to oxalate-extractable Fe, corresponding to amorphous or less crystalline Fe-oxides. The 5-step sequential extraction procedure (SEP), which was originally designed for As, and revised BCR SEP were applied to chemically fractionate Sb and As in the most polluted soil profiles. In forest soils, Sb was mostly bound in residual fraction with “mobile” concentrations in the range of 0.6–4% of the total Sb content. In contrast, As was significantly more mobile (1.2–22% of the total content in the “mobile” fractions) with dominant binding to Fe-oxides (up to 57% of total As content). In agricultural soils, Sb was again less “mobile” than As (1.4–5.9% and 0.34–12.1%, respectively of the total concentrations). Whereas Sb was mainly bound to the residual fraction and partly also in the reducible fraction (Fe-oxides), As was predominantly bound to Fe-oxides (up to 71% of the total As content). Good agreement was observed between the two SEP methods in determining the “mobile” concentrations of the metalloids (R2Sb = 0.9918 and R2As = 0.9104, p < 0.001). Despite probable similarities in the geochemical behaviour of these two metalloids in polluted soil systems, this study indicates that As is chemically more mobile than Sb.