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- Title
Influence of Atmospheric Oxygen on Heavy Metal Mobility in Sediment and Soil.
- Authors
Zehl, Katharina; Einax, Jürgen W.
- Abstract
Background, Aims. Pollution of sediment and soil by heavy metals is still an environmental problem. In order to assess the actual environmental risk, the mobile and biologically available content of heavy metals needs to be determined rather than the total content. This requires an analytical strategy preserving the actual binding forms of the heavy metals. Sampling and sample preparation are usually carried out in the presence of oxygen. As a consequence, oxidation of the metal and/or its binding partners is possible under these conditions, changing the original binding character. Therefore, sampling and sample preparation must be performed under inert conditions. The influence of atmospheric oxygen on the heavy metal mobility in sediment and soil for Cd, Go, Cr, Cu, Fe, Mn, Ni, Pb, and Zn is shown for samples of different origin. By means of a case study, an alternative for the extensive inert sampling and sample preparation is given; also, a mobility correction factor for the heavy metals mentioned is determined. Methods. At selected sampling locations (soil, sediment, swamp) sampling was performed under inert conditions. All sample preparation steps are carried Out under inert (argon) as well as non-inert conditions. After a sequential extraction (modified BCR-scheme), heavy metals were measured in all extracts with ICP-MS and ICP-OES. The total aqua regia-soluble metal content was determined after microwave digestion. Results. The comparison between the inert and non-inert technique illustrates the importance of the expensive inert working procedure for a correct heavy metal risk assessment. The available contents of Gd, Pb, and Zn are higher under oxidative laboratory atmosphere than under on site conditions, thus entailing an overestimation of the actual risk of these ecotoxicologically relevant metals. This effect must be explained by the oxidation and/or destruction of the metal binding partners under the presence of oxygen. The free metal cation formed during the oxidation of sulfides, for example, will be extracted in the easily available fraction. On the contrary, Fe and Mn, and to a lesser extent Go and Ni, are underestimated. Their mobile contents are lower under non-inert conditions. The oxidation of Fe2+ and Mn2+ to Fe3+ and Mn4+ occurs under laboratory atmosphere. Because of the higher solubility of the bivalent forms of Fe and Mn compared to their oxidized forms, the higher available contents will be found under inert conditions where oxidation is not possible. Conclusion. Contaminated sediment and soil are often removed from a polluted area for deposition. The consequences of spontaneous oxidation are demonstrated by means of a cadmium contaminated site, a former luminescent plant in Bad Liebenstein, Thuringia (Germany). The cadmium contamination is estimated in the plant region by using geostatistical methods, in this case kriging estimation. In consideration of the overestimation of Cd mobility and implementation of a mobility correction factor, the real Cd mobility is calculated for this area. The polluted area decreases down to 49% compared to the original one. Outlook. The influence of atmospheric oxygen on the heavy metal mobility must be regarded for a correct heavy metal risk assessment. An alternative to the expensive inert working technique may be the implementation of a heavy metal mobility correction factor. All conventionally measured heavy metal contents can be corrected with this experimentally determined factor.
- Subjects
ENVIRONMENTAL protection; POLLUTION prevention; POLLUTION risk assessment; HEAVY metals; SOIL pollution; SEDIMENT capping; ATMOSPHERIC chemistry; PHYSIOLOGICAL oxidation; OXYGEN
- Publication
Journal of Soils & Sediments: Protection, Risk Assessment, & Remediation, 2005, Vol 5, Issue 3, p164
- ISSN
1439-0108
- Publication type
Article
- DOI
10.1065/jss2005.01.132