CERTIFIED REFERENCE MATERIALS FOR EXTRACTABLE TRACE-METALS IN SOILS -EFFECT OF THE PARTICLE-SIZE

Homogeneity of a soil reference material was tested at two different s tages of production: in the bulk material and after bottling. To incre ase homogeneity in the bottle, the material may be ground thoroughly, but this may change the material and consequently the extractable trac e metal content even the stability of the extractable contents over ti me may change. These effects were studied for Cd, Cr, Cu, Ni, Pb, and Zn using acetic acid and EDTA as extracting solutions. Hard grinding o f the soil increased or decreased the extractability of some heavy met als depending on the metal and the extractant, whereas the stability o f the material was not affected by this treatment, except for Cd when using EDTA. As the homogeneity achieved in bottle by a short manual sh aking was sufficient for the procedure studied, no hard grinding is re commended.