MEASUREMENT AND PREDICTION OF COPPER-ION ACTIVITY IN LAKE ORTA, ITALY

A commercial Cu ion selective electrode (ISE) mounted on a field conductivity, temperature, depth probe (CTD) equipped with pH and oxygen sensors was used to measure a profile of Cu ion activity [a(Cu2+)] in Lake Orta, Italy. Lake Orta water contains approximately 32-34-mu-g L-1 Cu from anthropogenic sources. Below the mixed layer, a(Cu2+) was directly related to the pH of the lake water. In the body of the hypolimnion, measurements of a(Cu2+) were in good agreement with estimates of a(Cu2+) obtained from total Cu concentrations. The pH dependence of the activity/concentration of free Cu2+ was modeled with a simple ion association model of the lake water. The results of the model were verified by a potentiometric titration of a sample of lake water using Cu, pH, and NH3 ISEs. The titration simulated a forthcoming chemical treatment now in progress.