Abstract
Water soluble and/or dissolved metals represent the most ecotoxicologically relevant fraction of metals in the environment. However, water extractions may be prone to errors. This study aims to evaluate the performance of 5 filters as well as Rhizon soil moisture samplers, with respect to metal adsorption and/or release by the filter. In addition, the effect of equilibration time on water extractions of different types of soils was evaluated (silty loam, silty clay loam, loamy sand). Filtrations of synthetic solutions containing 40 μg 1−1 Zn, 20 μg 1−1 Cu, Ni and Pb, 10 μg 1−1 Cr and 2 μg 1−1 Cd were conducted using the different filters. The synthetic solutions either contained (i) no other competitive cations (Ca, Mg, Na, K, Fe, Mn, Al) (A 1), (ii) competitive cations at concentrations similar to those observed in soil solutions (A 2), (iii) competitive cations at 10 times lower concentrations than those in the synthetic soil solution (A 3). Whiteband filters were observed to retain considerable amounts of trace metals (except Cr), both in the presence and absence of other competitive cations. Millipore filters did not exhibit metal retention. Rhizon soil moisture samplers did not retain trace metals from the synthetic soil solution (A 2), whereas at lower concentrations of competitive cations (A 1, A 3) retention of Cu and Pb was observed. Whiteband filters without a predefined pore diameter allowed colloidal material of unknown particle size to pass into the filtrate, making interpretation of results very difficult and comparison between studies using different filters impossible. Millipore filters with a predefined pore diameter are to be recommended for this purpose. However, particular attention must be paid to potential constitutive Zn release by the sintered glass filter holders, the effect of which can be reduced by rigorous acid washing prior to and following every use. Rhizon samplers were also considered to be useful tools with well-defined and sufficiently small pore diameters to withhold colloidal material. However, in the absence or at reduced concentrations of competitive cations (A 1, A 3) retention of trace metals by the Rhizons, particularly Cu and Pb, was observed. Finally, short equilibration times may be insufficient for full assessment of the water extractable pool of trace metals in the soil.
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Meers, E., Laing, G.D., Unamuno, V.G. et al. Water Extractability of Trace Metals from Soils: Some Pitfalls. Water Air Soil Pollut 176, 21–35 (2006). https://doi.org/10.1007/s11270-005-9070-1
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DOI: https://doi.org/10.1007/s11270-005-9070-1