Precursors of carcinogenic N-nitroso compounds in Lake Peipsi

The concentration of precursors of carcinogenic N-nitroso compounds, nitrates and nitrites as well as ammonia, in the surface water of Lake Peipsi and its tributaries has been determined during the period 1985-1988. The nitrate and nitrite content was also analysed in bottom sediments and fish from the lake. The nitrate concentration in the water of Lake Peipsi varied from 0.01 to 2.33 mg NO3-N 1(-1), the average value from 0.27 to 1.60 mg NO3-N 1(-1), with the lowest concentrations in summer. The variations may be caused by different pollution loads, meteorological conditions, and assimilation of nitrates by plants and algae. The nitrate content in the water of rivers was on an average somewhat higher in comparison with its concentrations in the lake. The concentrations of nitrites were, as a rule, about an order of magnitude lower than those of nitrates. The amount of ammonia varied from 0.15 to 0.36 mg NH4-N 1(-1). At present the concentrations of the studied nitrogen compounds are not essential and do not prevent from using the lake for recreation and drinking water supply.