Effect of heavy metals on self-purification processes in rivers

Abstract

The inhibitory effects of heavy metals on self-purification processes in surface water were studied. Toxicities of the metals were evaluated on the grounds of the results of the Biochemical Oxygen Demand (BOD) test in river water. The BOD inhibitions depended on the concentrations of metals and on the incubation time. After one day's incubation, a full inhibition was found to be caused by Ag at all tested concentrations above 0.02 mg.l-1 for Hg, Cd, Pb, and Cu above 1 mg.l-1, for Be above 2 mg.l-1, and for Co, Ni, and SnII above 5 mg.l-1. A strong inhibitory effect ranging from 50 to 80% was observed for Cd (from 0.2 to 0.7 mg.l-1), Cu (from 0.4 to 1.0 mg.l-1), Be (from 0.5 to 2.0 mg.l-1), Zn (from 1.2 to 5.0 mg.l-1), SnII (from 2.2 to 4.2 mg.l-1), and CrVI (above 4 mg.l-1). AsIII, AsV, MnII, SeIV and SeVI did not cause any BOD inhibition to 2 mg.l-1 (As) res. 5 mg.l-1 (other metals). The inhibitory effect of metals decreased significantly or disappeared with increasing incubation time. Being observed with all metals with toxic effects except for Be, SnII, and CrIII, the decrease was more intense at the beginning of the incubation period. © 2009, Penkala Bt., Budapest, Hungary.