Solubility of antimony and other elements in samples taken from shooting ranges

The aim of this study was to determine whether or not Sb and other elements (Ni, Cu, Bi, Tl, and Hg) originating from Pb alloy (2-5 wt. % Sb) bullets become more soluble as a result of weathering and what mechanisms possibly control their solubility. Samples were taken from bank material behind the targets at seven Swiss shooting ranges. The samples were dried, sieved, analyzed, and subjected to leaching experiments. Total average concentrations of Sb ranged from 0.5 to 13.8 g kg(-1). In the leaching experiments, Sb was almost exclusively present in solution as the oxidized species Sb(V) in concentrations of up to 5 mg L(-1). The Ca mineral Ca[Sb(OH)6]2 is suggested to control dissolved Sb(V) concentrations in soils at high concentrations. Oxalate extractions suggested that approximately 50% of Sb [predominantly Sb(V)] in the <0.5-mm fraction was adsorbed to Fe (hydr)oxides and possibly other minerals, such as calcite, that are soluble at pH 2. However, it is possible that only a fraction of the oxalate-extractable Sb(V) is reversibly bound to mineral surfaces. It was concluded that the release of Sb is significant and considerably higher than the other elements under investigation and that the mechanisms controlling Sb mobility should be further investigated.     

Joint influence of surfactants and humic matter on PAH solubility. Are mixed micelles formed?

Mobilization of polycyclic aromatic hydrocarbons (PAH) by surfactants, present at contaminated sites or deliberately introduced for remediation purposes, is inevitably associated with the influence of humic substances, which are ubiquitous in natural systems. Therefore, the solubilizing effects of anthropogenic and natural amphiphiles must be considered in their combined action since synergistic or antagonistic effects may be expected, for instance, as a consequence of mixed micellization.

In this paper, solubilization of ¹⁴C-labeled pyrene in single-component and mixed solutions of surfactants and humic acid (coal-derived) was investigated up to the micellar concentration range. At low concentrations, antagonistic effects were observed for systems with cationic as well as anionic surfactants. Solubility enhancements in the presence of humic acid were canceled on addition of a cationic surfactant (DTAB) since charge compensation at humic colloids entailed precipitation. Solubility was also found to be decreased in the presence of an anionic surfactant (SDS), which was attributed to a competitive effect in respect of pyrene–humic interaction. This explanation is based on octanol–water partitioning experiments with radiolabeled humic acid, yielding evidence of different interaction modes between humic colloids and cationic/anionic surfactants. At higher concentrations, the effects of humic acid and SDS were found to be additive. Thus, a formation of mixed micelles is very unlikely, which was confirmed by size exclusion chromatography of mixed systems. It can be concluded that remediation measures on the basis of micellar solubilization are not significantly affected by the presence of natural amphiphilic compounds.