Kerstin Hockmann

Effects of three amendments on extractability and fractionation of Pb, Cu, Ni and Sb in two shooting range soils.

Contamination of shooting range soils with toxic trace elements, in particular Pb and Sb, is of increasing environmental concern worldwide. We studied the extractability of Sb, and other metals in two shooting range soils: a calcareous soil (pH 8) with low organic carbon (0.5%) and a non-calcareous soil (pH 6.3) with elevated organic carbon content (5%). Both soils contained total concentrations of around 500 mg kg(-1) Pb, 65 mg kg(-1) Cu, 100 mg kg(-1) Zn and 20 mg kg(-1) Sb. We tested the effects of Ca(OH)(2), phosphate and sodium humate amendments on metals and Sb extractability. Extracts with H(2)O and NaNO(3) contained 0.02-0.05% of the total Zn and Pb; 0.1-0.5% of total Ni and Cu and approximately 1% of total Sb. Sequential extraction procedure of Zeien and Brümmer resulted in similar percentages for the sum of the two most labile fractions (F1+F2) in two soils: 10% Pb, and 15-20% Sb. Water and NaNO(3)-extractable Sb concentrations increased after phosphate addition, but were not affected by the addition of sodium humate. The results show that leaching of Sb from shooting ranges into ground and surface waters may generate a serious environmental risk under widely different soils conditions.

Release of antimony from contaminated soil induced by redox changes

Soil contamination by toxic antimony (Sb) released from corroding ammunition has become an issue of public concern in various countries. Many of these soils are at least occasionally subject to waterlogging; yet mechanisms controlling Sb mobility under anaerobic conditions are still poorly understood. We investigated Sb concentration and speciation dynamics in a calcareous shooting range soil in terms of changing redox conditions using microcosm experiments. The transition to reducing conditions invoked by indigenous microbial activity at first led to the immobilization of Sb, as Sb(V) was converted to Sb(III), which binds more extensively to iron (hydr)oxides. When reducing conditions continued, the previously sorbed Sb(III) was gradually released into solution due to reductive dissolution of the iron (hydr)oxides. Speciation measurements in the solid phase by Sb K-edge XANES spectroscopy and in the soil solution by liquid chromatography ICP-MS provided the first evidence that Sb(III) predominated at low redox conditions (Eh <0.05 V) in both phases. The results show that Sb(V) is less stable in reducing environments than commonly assumed. Given that Sb(III) is generally more toxic than Sb(V), the mobilization of Sb(III) under Fe-reducing conditions may significantly increase (eco)toxicological risks arising from Sb-contaminated soils that are prone to flooding or waterlogging.

Accumulation of Sb, Pb, Cu, Zn and Cd by various plants species on two different relocated military shooting range soils

Annually, more than 400 t Pb and 10 t Sb enter Swiss soils at some 2000 military shooting ranges. After the decommission of military shooting ranges, heavily contaminated soils (>2000 mg kg(-1) Pb) are landfilled or processed by soil washing, whereas for soils with less contamination, alternate strategies are sought. Although the use of military shooting ranges for grazing in Switzerland is common practice, no assessment has been done about the uptake of Sb in plants and its subsequent potential intake by grazing animals. We determined the uptake of Sb, Pb, Cu, Zn and Cd in the aboveground biomass of nine plant species growing on a calcareous (Chur) and a weakly acidic (Losone) military shooting range soil in order to assess if grazing would be safe to employ on decommissioned military shooting ranges. The two soils did not differ in their total concentrations of Cu, Zn, Sb and Cd, they differed however in the total concentration of Pb. Additionally, their physical and chemical properties were significantly different. The accumulation of Zn, Cu, Cd and Pb in the shoots of all nine plant species remained below the Swiss tolerance values for fodder plants (150 mg kg(-1) Zn, 15-35 mg kg(-1) Cu, 40 mg kg(-1) Pb, and 1 mg kg(-1) Cd DW), with the only exception of Pb in Chenopodium album shoots which reached a concentration of 62 mg kg(-1) DW. Antimony concentrations were 1.5-2.6-fold higher in plants growing on the calcareous soil than on the weakly acidic soil. Considering Cu, Zn, Pb, Sb and Cd, all plants, with the exception C. album, would be suitable for grazing on similar shooting range soils.

Antimony retention and release from drained and waterlogged shooting range soil under field conditions

Many soils polluted by antimony (Sb) are subject to fluctuating waterlogging conditions; yet, little is known about how these affect the mobility of this toxic element under field conditions. Here, we compared Sb leaching from a calcareous shooting range soil under drained and waterlogged conditions using four large outdoor lysimeters. After monitoring the leachate samples taken at bi-weekly intervals for >1.5 years under drained conditions, two of the lysimeters were subjected to waterlogging with a water table fluctuating according to natural rainfall water infiltration. Antimony leachate concentrations under drained conditions showed a strong seasonal fluctuation between 110 μg L(-1) in summer and <40 μg L(-1) in winter, which closely correlated with fluctuations in dissolved organic carbon (DOC) concentrations. With the development of anaerobic conditions upon waterlogging, Sb in leachate decreased to 2-5 μg L(-1) Sb and remained stable at this level. Antimony speciation measurements in soil solution indicated that this decrease in Sb(V) concentrations was attributable to the reduction of Sb(V) to Sb(III) and the stronger sorption affinity of the latter to iron (Fe) (hydr)oxide phases. Our results demonstrate the importance of considering seasonal and waterlogging effects in the assessment of the risks from Sb-contaminated sites.

Effect of iron plaque on antimony uptake by rice (Oryza sativa L.)

Although iron (Fe) plaque has been shown to significantly affect the uptake of toxic antimony (Sb) by rice, knowledge about the influence of iron plaque on antimony (Sb) (amount, mechanisms, etc) is, however, limited. Here, the effect of Fe plaque on Sb(III) and Sb(V) (nominal oxidation states) uptake by rice (Oryza sativa L.) was investigated using hydroponic experiments and synchrotron-based techniques. The results showed that iron plaque immobilized Sb on the surface of rice roots. Although the binding capacity of iron plaque for Sb(III) was markedly greater than that for Sb(V), significantly more Sb(III) was taken up by roots and transported to shoots. In the presence of Fe plaque, Sb uptake into rice roots was significantly reduced, especially for Sb(III). However, this did not translate into decreasing Sb concentrations in rice shoots and even increased shoot Sb concentrations during high Fe-Sb(III) treatment.

Antimony leaching from contaminated soil under manganese- and iron-reducing conditions: column experiments

Environmental context Contamination of shooting range soils by antimony (Sb) released from corroding ammunition has become an issue of public environmental concern. Because many of these sites are subject to waterlogging and consequently limited aeration, we performed column experiments with contaminated shooting range soil to investigate Sb mobility under such conditions. The results are important for our understanding of the risks arising from Sb-contaminated soils, and also for the derivation of appropriate management strategies for such sites. Abstract Despite the environmental risks arising from antimony-contaminated sites, critical factors controlling the mobility of Sb in soils have still not been fully identified to date. We performed column experiments to investigate how reducing conditions affect Sb leaching from a calcareous shooting range soil, with a special focus on the relationship between Sb release and mineral dissolution processes. After eluting the columns for 5 days with 15mM lactate solution at a flow rate of 33mm day–1, the flow was interrupted for 37 days and then resumed for another 5 days. With the transition to moderately reducing conditions (~300mV) after 1 day of flow, effluent SbV and manganese (Mn) concentrations showed a concomitant increase, providing evidence that SbV associated to these phases was released by the reductive dissolution of Mn minerals. The release of SbV was counteracted by the reduction to SbIII, which was first scavenged by iron (Fe) (hydr)oxides and then slowly liberated again when the redox potential further decreased to Fe-reducing conditions. Laser ablation–inductively coupled plasma–mass spectrometry revealed the presence of an initial pool of Sb associated with Mn-containing, Fe-free phases, underpinning the important role of the latter in addition to Fe (hydr)oxides as Sb sorbents.

Arsenic Mobilization from Historically Contaminated Mining Soils in a Continuously Operated Bioreactor: Implications for Risk Assessment

Concentrations of soil arsenic (As) in the vicinity of the former Złoty Stok gold mine (Lower Silesia, southwest Poland) exceed 1000 μg g(-1) in the area, posing an inherent threat to neighboring bodies of water. This study investigated continuous As mobilization under reducing conditions for more than 3 months. In particular, the capacity of autochthonic microflora that live on natural organic matter as the sole carbon/electron source for mobilizing As was assessed. A biphasic mobilization of As was observed. In the first two months, As mobilization was mainly conferred by Mn dissolution despite the prevalence of Fe (0.1 wt % vs 5.4 for Mn and Fe, respectively) as indicated by multiple regression analysis. Thereafter, the sudden increase in aqueous As[III] (up to 2400 μg L(-1)) was attributed to an almost quintupling of the autochthonic dissimilatory As-reducing community (quantitative polymerase chain reaction). The aqueous speciation influenced by microbial activity led to a reduction of solid phase As species (X-ray absorption fine structure spectroscopy) and a change in the elemental composition of As hotspots (micro X-ray fluorescence mapping). The depletion of most natural dissolved organic matter and the fact that an extensive mobilization of As[III] occurred after two months raises concerns about the long-term stability of historically As-contaminated sites.

Antimony mobility during prolonged waterlogging and reoxidation of shooting range soil : a field experiment

Due to its increasing anthropogenic use, antimony (Sb) soil pollution is of growing concern. Many soils experience fluctuating hydrological conditions, yet very little is known about how this affects the mobility of this toxic element under field conditions. In this study, we performed an outdoor lysimeter experiment to compare Sb leaching from a calcareous shooting range soil under drained and prolonged waterlogged conditions (1.5-2.75years), followed by a 1.5-year period of soil reoxidation. Waterlogging reduced Sb leachate concentrations significantly compared to drained conditions and soil solution concentrations decreased with depth due to the increased reducing conditions. This was attributed to the reduction of Sb(V) to Sb(III) and the more effective sorption of the latter to metal (hydr)oxides. However, reductive dissolution of iron (hydr)oxides released Sb into solution, although Sb concentrations never exceeded those in the drained lysimeters. On reoxidation of the soil, Sb was remobilized, but even after 1.5years under reoxidised conditions, Sb leachate and soil solution concentrations still remained below those of the drained lysimeters. Our results demonstrate that prolonged waterlogging may have an irreversible effect on Sb leachate and soil solution concentrations.

Plant uptake and availability of antimony, lead, copper and zinc in oxic and reduced shooting range soil

Shooting ranges polluted by antimony (Sb), lead (Pb), copper (Cu) and zinc (Zn) are used for animal grazing, thus pose a risk of contaminants entering the food chain. Many of these sites are subject to waterlogging of poorly drained soils. Using field lysimeter experiments, we compared Sb, Pb, Cu and Zn uptake by four common pasture plant species (Lolium perenne, Trifolium repens, Plantago lanceolata and Rumex obtusifolius) growing on a calcareous shooting range soil under waterlogged and drained conditions. To monitor seasonal trends, the same plants were collected at three times over the growing season. Additionally, variations in soil solution concentrations were monitored at three depths over the experiment. Under reducing conditions, soluble Sb concentrations dropped from ∼50 μg L-1 to ∼10 μg L-1, which was attributed to the reduction of Sb(V) to Sb(III) and the higher retention of the trivalent species by the soil matrix. Shoot Sb concentrations differed by a factor of 60 between plant species, but remained at levels <0.3 μg g-1. Despite the difference in soil solution concentrations between treatments, total Sb accumulation in shoots for plants collected on the waterlogged soil did not change, suggesting that Sb(III) was much more available for plant uptake than Sb(V), as only 10% of the total Sb was present as Sb(III). In contrast to Sb, Pb, Cu and Zn soil solution concentrations remained unaffected by waterlogging, and shoot concentrations were significantly higher in the drained treatment for many plant species. Although showing an increasing trend over the season, shoot metal concentrations generally remained below regulatory values for fodder plants (40 μg g-1 Pb, 150 μg g-1 Zn, 15-35 μg g-1 Cu), indicating a low risk of contaminant transfer into the food chain under both oxic and anoxic conditions for the type of shooting range soil investigated in this study.