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Browsing by Author "Toco, Ester Masico"

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  • Ecotoxicological impacts of olive mill wastewaters on freshwater fauna of River Tua (NE Portugal)
    Publication . Toco, Ester Masico; Fernandes, Conceição; Teixeira, Amílcar
    Portugal stands out as one of the main olive oil producing countries, with the Trás-os-Montes region being particularly relevant due to its intense olive growing activity. Olive oil extraction generates significant volumes of liquid effluent, known as Olive Oil Mill Wastewater (OMWW). The predominant extraction system is two-phase, considered more environmentally sustainable as it produces smaller volumes of wastewater. According to Portuguese legislation, OMWW can be stored in evaporation ponds. However, although this practice is economically advantageous, it does not ensure effective environmental protection, particularly in aquatic ecosystems due to water contamination. To date, there are few studies evaluating the effects of OMW on macroinvertebrate and fish communities, particularly related to bioindicator changes (e.g. diversity, abundance, biotic indexes), as well as sublethal effects in terms of physiological biomarkers in sensitive native fish species, such as Luciobarbus bocagei. Given the risk of surface runoff or infiltration of these wastewaters into the aquatic environment, either by accidental discharges or by leaching processes, it is imperative to investigate their environmental impacts. In this context, the main objective of the present study was to evaluate the bioecological and toxicological impacts of wastewater from olive oil mills of 2 olive pomace oil extraction companies, located near Mirandela, on the aquatic fauna of the Tua River (Northeast Portugal). For the bioecological evaluation, 8 sampling sites were selected, grouped according to the degree of disturbance: 1) LOW, sites located upstream (T1, T2); 2) HIGH, sites located immediately downstream of the effluent entry point from both settling ponds (T3 and T6); and 3) INTERMEDIATE, sites located further downstream (T4, T5, T7 and T8). The methodologies defined by the Portuguese Environment Agency (APA), within the scope of the Water Framework Directive (WFD), were used to evaluate biological elements, such as macroinvertebrate and fish communities, as well as physical-chemical elements of the water, considering both the winter and summer sampling periods of 2024, As well as the subacute toxicity assay with Luciobarbus bocagei. The results of the bioecological assessment showed a significant decrease in water quality (high conductivity, phenols, oxidability and low pH), especially in the sampling sites located under the direct influence of the discharges of both olive pomace oil extractors (i.e., T3 and T6). The impact is also well expressed in several bioindicator metrics (e.g., richness, abundance, diversity, biotic indices IPTIN, F-IBIP) reinforced by statistical analyses confirming the biodiversity loss and substantial changes in the invertebrate and fish communities, particularly in native fish species, such as L. bocagei, suggesting a high sensitivity of this endemic species to water contamination. The results of the acute toxicity tests with Artemia franciscana revealed high toxicity of OMW, regardless of the season. Subsequently, additional acute toxicity tests were performed with Luciobarbus bocagei, using OMW samples collected in summer and winter. Exploratory tests with summer samples showed that concentrations between 0.5% and 5% induced significant toxic effects in exposed individuals. In a second test of a subacute nature, physiological responses were evaluated by quantifying plasma electrolytes (Na⁺, Ca²⁺ and K⁺) after 24 and 48 hours of exposure. Plasma electrolytes were selected as biomarkers due to their high sensitivity to disturbances in ionic homeostasis, often caused by environmental pollutants. This choice is justified by the central role of the gills in osmoregulation, since they are in direct contact with the aquatic environment and represent one of the first organs to react to chemical stress. Changes in plasma sodium, calcium and potassium concentrations may therefore indicate impairment of essential physiological functions and ion regulation capacity. The results showed significant changes in potassium (K⁺) levels, while calcium (Ca²⁺) and sodium (Na⁺) levels did not show relevant variations. This lack of response may be due to technical limitations, such as the reduced blood volume available resulting from the small size of the specimens (13–14 cm) and the decline in phenolic compound concentrations observed throughout the test in the test tanks. It is important to emphasize that the absence of variation in some parameters does not imply the absence of stress, since L. bocagei can activate compensatory mechanisms of physiological adaptation to adverse environmental conditions.
    2025Master thesis Open access Show more