Efeitos da adição de N e P na degradação da cafeína por bactérias no Lago dos Manacás

Abstract

Caffeine is an emerging contaminant and an indicator of anthropogenic activities. The concentrations of this substance in aquatic ecosystems have become a concern due to its potential risks to biota in these environments. Little is known about caffeine degradation in aquatic environments, but aquatic bacteria play a crucial role in organic matter degradation. Therefore, understanding the dynamics of caffeine degradation by aquatic bacteria can provide insights for mitigating the effects of caffeine in water sources and managing this emerging contaminant. The objective of this study was to assess the effects of Nitrogen and Phosphorus addition on caffeine degradation by aquatic bacteria. Water samples were collected from Manacás Lake in Juiz de Fora. Five treatments were established with the addition of commercial caffeine and Nitrogen and Phosphorus nutrients separately and in combination, along with two controls (without nutrient or caffeine addition). The samples were incubated in the dark at room temperature for 4 weeks. Water samples were collected on days 0, 3, 7, 14, and 21 to determine caffeine concentrations. Dissolved oxygen concentrations were analyzed on days 0 and 3 to determine bacterial respiration rates as a measure of organism metabolism. Nitrogen addition did not result in caffeine degradation throughout the experiment, nor did the treatment with caffeine alone. In contrast, treatments with Phosphorus addition and combined Nitrogen and Phosphorus addition resulted in total caffeine degradation between 3 and 7 days of incubation. Bacterial respiration was lower in treatments with Nitrogen or Phosphorus addition alone compared to other treatments and the control. This suggests that the increased caffeine degradation due to Phosphorus addition may not necessarily result from higher bacterial metabolism. However, it is necessary to understand the effects of these treatments on the energy balance between respiration and bacterial biomass production (i.e., bacterial growth efficiency) to better comprehend the relationship between nutrient addition and caffeine degradation. We conclude that Phosphorus was a limiting nutrient for caffeine degradation under the conditions of this study.