ION-SELECTIVE ELECTRODE MEASUREMENTS OF COPPER(II) ACTIVITY IN CONTAMINATED SOILS

A method is presented for the use of a cupric ion-selective electrode to determine the free copper activity in 0.01 M CaCl2 soil solution ex tracts. Ionic strength variations and the presence of aluminum caused no significant interferences. The method was applied to 18 soils with wide-ranging copper levels. The pCu(2+) varied between 6.33 and 12.20. Acidic soils have a very high cupric ion activity even though they ar e not considered to be contaminated with copper. Soils considered cont aminated with respect to total copper also have free pCu(2+) activitie s below 10, which is close to the toxicity threshold determined in aqu atic ecotoxicological studies. All mineral soils have free copper acti vities close to or below the values expected from pH-dependent soil eq uilibration studies.