This chapter contains information related to the oxidation-reduction potential (ORP) in aqueous solutions, aiming to extend some aspects from theoretical electrochemistry to practical environmental monitoring and engineering applications. A more comprehensive and precise continuous monitoring of water quality for groundwater, surface water, wastewater, and drinking water could be achieved by deducing relations between ORP, the concentration of the oxidants and reductants in waters, pH, and temperature, delivering valuable information for the better comprehension of the requirements necessary to design an automated water quality monitoring system with real-time transmitted data, assuring better water governance. Such a system is presented as a case study related to an early warning of preliminary ecotoxicity. The case study was conducted by installing water pollution monitoring equipment on a passenger ship sailing on the Sulina Channel in the Danube Delta, Romania.
TopIntroduction
Complex processes occur in the extensive ecosystems of natural protected areas. An example is the Danube Delta, a territory mainly under the jurisdiction of Romanian state authorities. The Danube Delta Biosphere Reserve was the first natural site in Romania to be registered in 1991 on the United Nations Educational, Scientific, and Cultural Organization (UNESCO) World Heritage List. The composition and properties of the surface waters in this ecosystem are not influenced by anthropic factors (Cretescu et al., 2022a). Complex processes (Duca et al., 2003) occur in a vertical direction, from the surface to the bottom, strongly influenced by solar radiation and specific phenomena at the interfaces between soil/water and water/air. Numerous biological and chemical processes must be considered together with physical actions: gas dissolution (oxygen and carbon dioxide) in water, evaporation/transpiration processes, and many others.
The self-cleaning capacity of the waters from complex aquatic ecosystems is well known (Duca et al., 2002) as a natural process of pollutant cleansing. These natural ecosystems are characterized by a unique, smart balance in the habitats between the diverse components of their biota. In waters where such a biological habitat exists, only the normal vital activity and development of hydrobionts at different trophic levels occur. In contrast, anthropogenic pollution from toxic and dangerous compounds threatens aquatic life and the trophic chain. Persistent organic compounds and heavy metal ions have harmful ecological impacts and generate ecotoxicity. The self-purification phenomena can be disturbed or even fully inhibited. If additional measures to manage water pollution are not implemented, the pollution gradually increases until it reaches, in the extreme, complete eutrophication of the water. Eutrophic water drastically reduces water use and has a strong negative ecological impact on the ecosystem, which is costly to reverse.
Numerous specific offline analytical methods and rapid tests to determine the ecotoxicity of water (Gregorin et al., 2021) have been developed by several manufacturers (EBPI, n.d.; Modern Water, n.d.), allowing measurement of the toxicity created by a wide range of harmful pollutants. The procedure for rapid tests comprises the collection of water samples, mixing them with the specific reagents from the kits, and obtaining the results. The results comprise changes in measurable parameters (e.g., color, turbidity, temperature, pH, etc.) after storage under specified conditions (e.g., incubation at a constant temperature, darkness, absence/presence of oxygen, shaking). In addition to the high cost of analytical kits and the high investment costs of offline analyzers, such methods for detecting ecotoxicity are generally difficult and involve considerable time and resource consumption.