EFFECTS OF COPPER, CADMIUM, LEAD AND ZINC ON NITRATE REDUCTION IN A SYNTHETIC WATER MEDIUM AND LAKE WATER FROM NORTHERN SWEDEN

This paper presents laboratory experiments on the effects of heavy metal on nitrate reduction, using natural lake water or a synthetic water medium without complexing agents. A bacteria inoculum consisting of a mixed facultatively heterotrophic bacterial culture, nitrate and glucose were added to tubes, which were filled to capacity, sealed and incubated in the dark at 20-degrees-C. Nitrate reduction was followed in terms of the decrease in added nitrate against time. For the synthetic water medium, the effects of Cd, Zn and Pb at concentrations of 10-500-mu-g l-1 were tested and for Cu at concentrations between 10 and 100-mu-g l-1. Nitrate reduction in natural lake water with and without additions of an external bacterial culture was measured. The effect of an addition of 50-mu-g l-1 of metal above the natural level was also investigated. In synthetic water, a 50% decrease in nitrate reduction activity was found at about 25-mu-g Cu l-1, 85-mu-g Cd l-1, 95-mu-g Pb l-1 or 200-400-mu-g Zn l-1. The order of toxicity was Cu > Cd > = Pb > Zn. In the lake water, nitrate reduction activity decreased with increasing metal levels. From the experiments involving the addition of metal to lake water the order of toxicity was found to be Cu > Cd > = Pb > Zn.