Analisi Ecotossicologiche su WWTP Civili e Industriali: Test Acuti e Cronici Combinati in Indici Integrati

In the last twenty years, thousands of research papers covering different aspects of emerging contaminants (also called micropollutants) have been published, ranging from environmental occurrence to treatment and ecological effects. Since wastewater treatment plants (WWTPs) are addressed as the main micropollutants point-sources, in this work, acute and chronic bioassays are performed in order to evaluate efficiency in 5 WWTPs located in Northern Italy, that flow into a Collector. The main aim is to investigate ecotoxicity levels of wastewaters and to assess the hazard for the receiving water body, enabling its protection through potential remedial actions to be adequately undertaken by decision-makers. Ecotoxicology is essential to evaluate the potential for adverse ecological effects that may occur as a result of exposure to contaminants or other stressors, thus leading to predict effect of pollution on environment: such predictions couldn't be made with the only means of chemical analysis, as they can't consider the occurrence of multiple chemicals as mixtures, or unknown toxic compounds. Since a single species-bioassay cannot adequately reflect pollution effects in the ecosystem, an acute test battery (with Raphidocelis subcapitata, three land plants, Daphnia magna, Vibrio fisheri) and a chronic test battery (with R. subcapitata, Lepidium sativum, D. magna, Lumbriculus variegatus) are adopted, by testing several organisms representing different trophic levels and different taxa. Among acute tests, D. magna was the least sensitive organism, while R. subcapitata showed the highest inhibition values. In chronic ones instead, a great biostimulation in D. magna was accompanied by inhibition in L. variegatus: both effects are addressed to be caused by the presence of micropollutants. Values obtained from tests were then used to elaborate integrated indexes, developed for both chronic and acute test batteries, which provide an integrate information related to the toxicity of each individual discharge. According to acute indexes, toxicity abatement was generally good along the WWTPs path, with a decrease in toxicity scores especially in Collector (where ¿negligible¿ judgements were always obtained); on the other hand chronic integrated indexes achieved on Collector showed that the toxicity increases greatly from acute to chronic analysis. These findings lead to three main conclusions: firstly, chronic tests can provide different information compared to acute test; in fact, where an acute test can return an absence of toxicity as a result, a chronic test can highlight the presence of a impairment in the form of biostimulation (as what happened in Daphnia). Secondly, it seems clear that chronic bioassays have greater sensitivity than acute ones; such statement agrees with what several authors reported: acute tests are not sensitive enough for treated wastewaters, while a certain hazard can be highlighted in chronic testing. Moreover, micropollutants exhibit generally low acute toxicity, even though several of them have been shown to cause significant reproductive effects on test organisms at very low levels and long-term exposure. These facts point out the importance of performing chronic bioassays even though they are more time consuming and require greater commitment and costs. Finally, ecotoxicology is effective in monitoring the efficiency of treatments and can identify situations of non-optimal abatement of substances.