Abstract

Nitrogen is an important chemical element due to biological reactions, including nutrient cycling. This process transforms organic matter into food for plants and other organisms. Some species can absorb the ammonium ion, but this one presents high toxicity. The portion that is most absorbed is nitrate due to its low toxicity, which is generally found in soils, industrial flows and fertilizers. However, the ion presents a danger to human health when present in concentrations higher than 10mg L-1 of N-NO3-, as determined by Resolution 357/2005 of CONAMA in meat, mineral water, and aquatic environments. In the present study conducted in rivers of the cities of Paranaguá and Pontal do Paraná, the ion was determined spectrophotometrically at 545nm by the Griess method, with pre-reduction of the nitrate in nitrite, using the metallic zinc as a reducing agent. All the samples evaluated presented values ​​below the limit recommended by CONAMA. These values ​​ranged from 0.03 to 0.69mg L-1 in the low season (September 2016) and 0.00 to 0.07mg L-1 in the high season (March / 2017). The obtained results were compared to others published and that present characteristics similar to the evaluated rivers. It was observed that NO3- concentrations have been increasing continuously, even in small proportions, confirming the occurrence of the eutrophying process.

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