Decreased metal concentrations in ground water caused by controls of phosphate emissions

Abstract

A NEW generation of phosphate-eliminating sewage treatment plants and the recent prohibition of phosphates in detergents have considerably reduced the concentrations of phosphate in surface waters¹. But there has been concern that replacing phosphate in detergents with complexing agents might cause increased mobilization of heavy metals, and consequent pollution of ground waters^2,3. Here we present a twelve-year analysis of phosphate, manganese and cadmium in the river Glatt, Switzerland, and in an adjacent aquifer which is infiltrated by the river water. Together with a reduction of phosphate concentrations in both river and ground water over the study period, we find lower ground water concentrations of manganese and cadmium. We postulate that lower phosphate levels have decreased the amount of oxidizable organic carbon in the river bed, and hence havecreated less reducing conditions in the infiltrating water. This in turn has resulted in decreased reductive dissolution of manganese and cadmium in the ground water. It thus appears that eliminating phosphate has led to an unexpected improvement in drinking water quality with respect to heavy metals.