Avaliação de risco ecológico em área alagada contaminada por gasolina.

Abstract

Benzene, toluene, ethylbenzene and xylene (BTEX), major components of gasoline, are commonly found in soil and groundwater contaminated by accidents in transport pipelines or storage tanks. The Ecological Risk Assessment (ERA) is an important tool for managing contaminated areas by identifying the adverse effects of contaminants in the environment. The aim of this study was to develop an ERA framework comprising the environmental compartments surface water, sediments and groundwater in an area of intermittent flooding, potentially affected by accidental gasoline spillage. The framework was based on the triad methodology by integrating results of three lines of evidence (LoE) chemical, ecotoxicological and ecological, to estimate the Environmental Risk (EnvRI). We selected 9 points of surface water and sediments within the flooded area; a tenth point was considered reference of an area not affected by contamination. For groundwater, 8 monitoring wells were selected and a ninth well was considered as reference. Sampling campaigns were conducted in December 2012, July and October 2014 and February 2015. The chemical LoE included results from the analysis of metals, BTEX and naphthalene; the ecotoxicological LoE was analyzed by acute (Aliivibrio fischeri, Daphnia similis and Hyalella azteca) and chronic bioassays (Artemia salina, Desmodesmus subspicatus and D. similis). In water samples, the ecological LoE evaluated endocrine disruption and genotoxicity by using biomarkers in (Nile tilapia). In sediments, the potential of oil biodegradation by the indigenous microbiota of the area was evaluated. Results of the chemical LoE indicated that the level of risk associated with contamination by gasoline was sharply reduced in the surface water and sediment of the flooded area between 2012 and 2015. Groundwater, however, proved to be the compartment most affected by the accident, showing free-phase gasoline, high concentrations of BTEX and naphthalene, "and in this way" maintaining the level of extreme chemical hazard. The volatilization processes during samples handling and time duration were responsible for the underestimation of contaminant concentrations at which the organisms are exposed. Results of acute and chronic bioassays of the ecotoxicological LoE indicated reduction in the level of risk of surface water and sediment between 2012 and 2015. For the groundwater, the ecotoxicological level of risk showed reduction inferior to 10%, remaining in the category of extreme hazard. Biomarkers analyses indicated endocrine disrupting effects and genotoxicity in O. niloticus exposed to surface water and groundwater samples in all campaigns, including in points / wells considered uncontaminated. In 2015, even in the absence of contaminants of interest, the ecological level of risk exhibits no variation in surface water samples. There was an increase of ecological risk by 35% for underground water. Results of tests with the oil degrading microbiota suggests low potential for bioremediation of the flooded area. In general, the AmbRI for surface water and sediments remained moderate / absent. However, the result of the three LoEs pointed out to an extreme level of risk in the groundwater, indicating the urgent need for remediation actions on the site.