SUCTION CUP MATERIALS AND THEIR POTENTIAL TO BIAS TRACE-METAL ANALYSES OF SOIL SOLUTIONS - A REVIEW

We reviewed the effects of physical and chemical characteristics of fi lter materials on trace metal concentrations in soil solutions to eval uate their suitability for porous sections of suction cups, Among the materials described in the literature, e.g, ceramics, Al2O3, sintered Ni or glass, and various plastic filters, a great variation in bubblin g pressure, pore size, permeability, chemical composition and stabilit y, CEC, and trace metal dissolution/precipitation or adsorption/desorp tion processes was found. A low adsorption capacity suggests plastic m aterials are suitable, provided the bubbling pressure is high enough. All other materials have disadvantages in one or more properties, e.g. release of trace metal impurities into the soil solution, clogging of pores by precipitation of previously dissolved compounds, or sorption of trace metals. Many reported experiments on sorption of trace metal s by various materials are not relevant because of the unrealistic hig h metal concentrations of the test solutions. Our experiments with rea listic concentrations revealed that sorption processes during the extr action may alter trace metal concentrations in soil solutions signific antly. Ceramic or Al2O3 cups are commonly used, but they adsorb apprec iable amounts of trace metals. Therefore, we conclude that metal fluxe s and budgets based on such data have to be interpreted with caution. To improve data comparability, detailed description of suction cup mat erials in the method sections of papers would be required. Moreover, m ore development and testing with plastic materials should be done, aim ed at the optimization of both physical and chemical properties.