CHAPTER TEN - OVERVIEW OF SELECTED SOIL PORE WATER EXTRACTION METHODS FOR THE DETERMINATION OF POTENTIALLY TOXIC ELEMENTS IN CONTAMINATED SOILS: OPERATIONAL AND TECHNICAL ASPECTS

Chemical elements that are either present naturally in the soil or introduced by pollution are more usefully estimated in terms of ‘availability’ of the element, because this property can be related to mobility and uptake by plants. A good estimation of ‘availability’ can be achieved by measuring the concentration of the element in soil pore water. Recent achievements in analytical techniques allowed to expand the range of interest to trace elements, which play a crucial role both in contaminated and uncontaminated soils and include those defined as potentially toxic elements (PTE) in environmental studies. A complete chemical analysis of soil pore water represents a powerful diagnostic tool for the interpretation of many soil chemical phenomena relating to soil fertility, mineralogy and environmental fate. This chapter describes some of the current methodologies used to extract soil pore water. In particular, four laboratory-based methods, (1) high-speed centrifugation-filtration, (2) low (negative-)-pressure Rhizon™ samplers, (3) high-pressure soil squeezing and (4) equilibration of dilute soil suspensions, are described and discussed in detail. A number of operational factors are presented: pressure applicable (i.e. pore size involved), moisture prerequisites of the soil, pore water yielding, efficiency, duration of extraction, materials and possible contaminations for PTE studies. Some consideration is then taken to assess advantages and disadvantages of the methods, including costs and materials availability.