Assessment of the acute toxicity of eutrophic sediments after the addition of calcium nitrate (Ibirite reservoir, Minas Gerais-SE Brazil): initial laboratory experiments

Autor(es)

Janke, H. ^[1] ; Yamada, T. M. ^[1] ; Beraldo, D. A. S. ^[1] ; Botta, C. M. R. ^[2] ; Nascimento, M. R. L. ^[3] ; Mozeto, A. A. ^[1]

Afiliação do(s) autor(es)

^[1] Univ Fed Sao Carlos UFSCar, Dept Quim, Nucleo Estudos Diagnost & Intervencoes Ambientais, Lab Biogeoquim Ambiental, BR-13565905 Sao Carlos, SP - Brazil

^[2] Univ Sao Paulo, CRHEA, Lab Ecotoxicol, Sao Carlos, SP - Brazil

^[3] CNEN, Lab Pocos de Caldas, Pocos De Caldas, MG - Brazil

• Tipo de documento: Artigo Científico
• Fonte: Brazilian Journal of Biology; v. 71, n. 4, p. 903-914, NOV 2011.
• Citações Web of Science: 10

Resumo

This study evaluated the acute toxicity of sediment in a eutrophic reservoir after remediation with a calcium nitrate solution to retain phosphorus. The study involved microcosms of surface sediments and water from the sediment-water interface in the Ibirite reservoir. This reservoir, located in the vicinity of metropolitan Belo Horizonte (Minas Gerais, SE Brazil), is a water body that receives treated effluents from an oil refinery (REGAP-Petrobras), as well as high loads of untreated urban effluents from the city of Ibirite and surrounding areas and industrial effluents from a major industrial park. Incubation times of the treatment experiments were: t = 0, t = 5, t = 10, t = 25, t = 50, t = 85 and t = 135 days. One control microcosm and three treated microcosms were analysed in each time interval. Acute toxicity of water samples was assessed with Ceriodaphnia silvestrii Daday, 1902 and that of bulk sediment samples with Chironomus xanthus Rempel, 1939. Toxicity tests were carried out concomitantly with chemical analyses of dissolved inorganic nitrogen species (ammonia, nitrate and nitrite), sulfate and metals in the water samples of the microcosms. Acid volatile sulfides (AVS), simultaneously extracted metal (SEM) and potentially bioavailable metal were analyzed in bulk sediment samples. Neither of the tested organisms showed toxicity in the control microcosm samples. The water column of the treated microcosm showed toxicity to C. silvestrii, starting at t = 10 days, while the sediment pore water toxicity started at t = 0 day. However, toxicity was found to decline from t = 85 days to t = 135 days. Sediments showed toxicity to C. xanthus during the entire experiment, except at the longest incubation time (t = 135 days). The overall results indicate that nitrate, which reached concentrations exceeding 1,200 mg N-NO3-L-1 in the sediment pore water of the treated microcosms, was most probably responsible for the toxicity of the samples. Although the calcium nitrate technology proved effective in retaining phosphorus, promoting sediment oxidation via denitrification, from the ecotoxicological standpoint and under the experimental conditions of this study, the application of nitrate for remediation of the sediments in the Ibirite reservoir did not prove effective up to a period of 135 days of incubation. However, we presume that after longer periods of incubation, treated sediments may recover their ability to sustain a benthic community. More advanced experiments are planned involving longer incubation times, thus extending the denitrification process, which may lead to a higher phosphorus retention capacity and to more complete abatement of sediment toxicity. (AU)

• Processo FAPESP: 07/52972-5 - Avaliação ecotoxicológica da adição de nitrato em sedimentos eutrofizados da represa de Ibirité (Betim-MG): experimentos em microcosmos
• Beneficiário: Helena Janke
• Modalidade de apoio: Bolsas no Brasil - Mestrado