Efeitos ecotoxicológicos de combustíveis em organismos fotossintéticos aquáticos e terrestres

Abstract

Fossil fuels and ethanol, although essential to the energy matrix and modern society, are significant sources of contamination in aquatic and terrestrial environments from spills and leaks. A portion of these contaminants becomes solubilized, forming the Water-Soluble Fraction (WSF), which is recognized as the most bioavailable and toxic fraction, as it directly interacts with organisms. Ecotoxicology, through the application of bioassays, constitutes a fundamental tool for assessing the adverse effects of contaminants on organisms, providing scientific support for monitoring programs and environmental management strategies. In this context, the present study aimed to evaluate the toxicity of the WSFs of regular gasoline, additive gasoline, diesel S10, and ethanol, as well as different dilutions of pure ethanol. The preparation of experimental solutions followed the guidelines of ABNT NBR 15469 (2007). In the assays with Desmodesmus subspicatus (NBR 12648, 2023), organisms were exposed for 72 h to concentrations of 25%, 5%, 1%, 0.5%, 0.1%, 0.05%, and 0.01% (v/v) for regular gasoline, ethanol, and additive gasoline, while specific dilutions were applied for diesel S10 (25%, 16.6%, 12.5%, 8.3%, 6.6%, 4.3%, and 2.8%). Endpoints included growth inhibition, median effective concentration (EC₅₀(72h)), no observed effect concentration (NOEC), and lowest observed effect concentration (LOEC). In the bioassays with Lactuca sativa, conducted over 120 h, seeds were exposed to the same concentration ranges (including pure ethanol) in Petri dishes. The parameters evaluated included germination and root growth, germination index (GI%), relative growth index (RGI), root elongation (RE), and inhibition percentage (%IN), all interpreted according to classification scales from the literature. Statistical analyses were performed using BioEstat® software, including ANOVA and post hoc tests. Results demonstrated high toxicity of pure ethanol (IC₅₀ < 0.01%), with strong inhibition of cell growth at low concentrations; high toxicity of the WSF of regular gasoline (IC₅₀ = 0.088%) and WSF of ethanol (IC₅₀ = 0.07%), followed by the WSF of additive gasoline (IC₅₀ = 0.097%) for D. subspicatus. Diesel S10 showed moderate toxicity (IC₅₀ = 27.2%). In L. sativa, significant alterations in germination and root growth were observed in response to the WSFs of gasoline and diesel, whereas the WSF of ethanol and pure ethanol caused intense phytotoxicity, with marked inhibition of seed development. It is concluded that the use of WSF represents an ecologically realistic methodological approach to simulate the bioavailability of fuels in aquatic environments. The association of D. subspicatus and L. sativa proved effective incharacterizing the ecotoxicological effects of fossil fuels and ethanol, providing relevant evidence for environmental risk assessment and for the formulation of public policies aimed at preventing and mitigating impacts on aquatic and terrestrial ecosystems.