BS ISO 22190:2020 pdf download – Soil quality — Use of extracts for the assessment of bioavailability of trace elements in soils It is noteworthy that this document suggests methods, i.e. soil extracts, based on an equilibrium approach. Indeed, the time course of the different extraction methods is usually long enough to reach the equilibrium between trace elements in the soil solid-phase and the water phase. Consequently, these methods are only suitable for the assessment of the environmental bioavailability when this is driven by soil equilibria rather than by kinetic constraints (non-equilibrium approach). 4.1.2 Neutral extracts for measurement of actual availability (ISO 21268- 1) For regulatory purposes simple and cheap methods are required and a simple extraction that simulates the pore water quality is desirable. A neutral aqueous solution (i.e., limiting changes of the soil pH during extraction as much as possible) can be used for this purpose. The concentration of trace element measured in a neutral extract is assumed to reflect the concentration in the pore water [as well as ionic strength, temperature, pH, DOC (Dissolved Organic Carbon)]. These properties may show a variation during the year and can be influenced by external factors (e.g., rain, drought, addition of manure). Extraction of a soil sample with demineralised water may have impact on the soil. For the purpose of estimating the actual availability of trace elements, it is desirable to reduce the influence of external factors and to obtain data that are more independent of the time of sampling. Extraction procedures have been developed using aqueous solutions containing a fixed concentration of a specific salt (neutral extract) in order to simulate the soil pore water. The stronger the extract (high ionic strength), the higher the amount of trace element released from the soil solid phase. On the other hand, the concentration of extracted DOC is also dependent on the choice of the neutral extract especially the concentration of divalent cations (Ca 2+ ) affects DOC. The ratio soil/ extract also affects the DOC concentration [4] . With a higher amount of DOC extracted, a higher amount of extracted trace elements can be expected, especially trace elements with a high affinity for binding to DOC (e.g. Cu, Pb, Cr). Originally 0,01 mol/l CaCl 2 has been applied as neutral extractant. For several soils this methods reflects the pore water concentration [5][6][7][8] . A concentration of 0,01 mol/l CaCl 2 is often...
Download Address
Download