Ecotoxicology in Water Quality Monitoring and As a Tool for Environmental Forensics
Understand more about ecotoxicology
Published on 11/20/2020
< Ecotoxicological analyses of surface waters allow the prediction, detection, qualification and quantification of the acute and/or chronic effect(s) caused by a sample to test organisms. Among the effects, or "endpoints", measured by the various ecotoxicological tests are: mortality, motility, endocrine disruption, change in growth rate or morphology, reproductive impairment, etc. (ADAMS; GREELEY, 2000; MARTINEZ-HARO et al., 2015; BOGER et al., 2016). Such effects are detected and quantified by performing toxicity tests that consist of exposing carefully selected and cultured test organisms to the environmental sample under controlled conditions (pH, DO, photoperiod, temperature, etc.). In this way, the results obtained through these tests reflect the synergistic effects caused by toxic substances that may be present in a given environment or sample.
Ecotoxicology as an investigative tool in the measurement of environmental impacts can be a great ally in forensics related to the occurrence of events that impact fauna. After all, such analyses allow the detection and quantification of acute and chronic toxic effects, which are related to the presence of the tailings in the river and its sediments, on aquatic fauna, in order to contribute to the elucidation of the mode of action of the pollutants.
Additionally, the analysis of water quality based only on physical-chemical parameters does not reflect the ecological picture of water bodies, and the monitoring of ecological and ecotoxicological parameters is essential to complement the information obtained from the physical-chemical parameters (ADAMS; GREELEY, 2000). In order to contribute to the environmental integrity of European waters, the WFD 2000/60/EC imposes the simultaneous monitoring of ecological and ecotoxicological parameters since the year 2000 (EU, 2000). Similarly, total toxicity analyses of effluents discharged into water bodies have been mandatory since 1991 in the United States (USEPA, 1991).
< The monitoring of water quality by ecotoxicological analyses, the object of the present research, is of extreme importance in the context of environmental occurrences such as the breach of a dam. Ecotoxicological tests aim to evaluate the toxicity of a pollutant, a mixture of pollutants or an environmental sample, in order to understand and quantify the effect caused and the risk presented by them to aquatic organisms at different trophic levels (MARTINEZ-HARO et al., 2015; WERNERSSON et al.,2015).
Ecotoxicological analyses can be performed in vitro or by exposing a cell or test organism to the evaluated sample (surface water, raw or treated effluent, synthetic solution, mining tailings, water contaminated with effluent or tailings, etc. ) for a standardized time and under defined conditions (pH, temperature, dissolved oxygen). In this way, it is possible to detect both acute toxicity, - that for which the effect is detected in hours (24, 48, 96h), - and chronic toxicity - when the effect is observed at some point throughout the life cycle of the test organism (MAGALHÃES; FERRÃO-FILHO, 2008).
There are several acute and chronic toxicity tests already standardized by international standards (ISO), and the most commonly used for water and wastewater samples and are the Microtox® assay, which assesses acute toxicity to the marine bacterium Allivibiro fischeri (ISO, 2007; ABNT, 2012), and the acute (48 hours) and chronic toxicity tests that use the crustacean Daphnia magna (21 days) ( ISO, 2012; ABNT, 2016a;) or Ceriodaphnia spp. (7 days) (CETESB, 2017). Acute toxicity tests have as their main result the CE50 - concentration that causes effect to 50% of the population. While the chronic toxicity tests allow the quantification of the Unobserved Effect Concentration (CENO) - maximum concentration that does not cause effect - and the Observed Effect Concentration (CEO) - minimum concentration that causes effect. The environmental application of CENO consists in its adoption as a safe concentration for a given pollutant in the environment and in the evaluation of environmental impacts caused in the long term by certain pollutants (MAGALHÃES; FERRÃO-FILHO, 2008).
Regarding national legislation, the CONAMA 357 resolution of 2005 requires the absence of chronic toxicity in Class 1 and 2 waters and of acute toxicity for Class 3 waters and provides for toxicity tests for substances that are not in the scope of the legislation. However, there is no definition of the toxicity tests that should be used in monitoring (CONAMA, 2005). CONAMA 430 of 2011, which provides for the standard of effluent discharge, establishes the performance of ecotoxicological tests in the effluent and at the mixing point of the receiving body for at least two distinct trophic levels (CONAMA, 2011), without however specifying the type of test.
< The carcinogenic effect of many different contaminants in water, including metals, can be evaluated by in vitro assays, such as in carcinogenicity tests. This evaluation is essential in order to determine the long-term effect of these contaminants, because they are not immediate and the biological mechanisms, such as biochemical and genomic, involved are extremely complex. However, considering that tests to evaluate carcinogenicity are time-consuming and extremely expensive, tests to evaluate mutagenicity and genotoxicity are more employed, since they determine the carcinogenic potential of the sample (HARTWIG et al., 2002; ASMUSS et al., 2000; CHEN & WHITE, 2004; GOODSON et al., 2015; UMBUZEIRO et al., 2017). The use of tests validated by international guidelines, such as those of the OECD (Organization for Economic Co-operation and Development), are recommended and applied for this purpose.
The ecotoxicological studies were conducted in the face of recent occurrences of iron ore mining dam breaches in the State of Minas Gerais in the period 2015-2019. The analyses were carried out in order to quantify the impacts resulting from these events on the affected watersheds and contemplated both the ecotoxicological analysis of samples of surface water and tailings, of sediments from rivers affected by the ruptures and in the watersheds impacted by the intense mining activity. Such studies used assays performed with organisms of different trophic levels and methods in vitro , As well as the trials being performed in the present research.
< Thus, the use of different ecotoxicological assays at different trophic levels, associated with a physicochemical characterization of the environmental samples, becomes indispensable for obtaining safe and precise answers regarding the ecotoxicological effect of an episode of environmental contamination.
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