The study measured nitrate and nitrite levels in rivers entering Taham dam in Zanjan, Iran. The researchers found that the concentrations of nitrate and nitrite were within safe limits set by WHO and Iran guidelines. The health-risk assessment showed that the levels of these compounds were not harmful to human health, with the Hazard Index values being below 1. This means that the nitrate and nitrite in the rivers do not pose a risk of causing cancer or other health issues.