Diclofenac sodium aqueous systems at low concentrations: Interconnection between physicochemical properties and action on hydrobionts.

Diclofenac sodium (DS) is a widely used nonsteroidal anti-inflammatory drug (NSAIDs). NSAIDs are poorly removed during standard wastewater treatment. The consequences of the presence of NSAIDs in rivers and lakes at 10^-11-10^-8 mol/L are not yet established; therefore, ecotoxicologists have focused their efforts on studying the effect of low-concentration NSAIDs on fish and hydrobionts, and also on predicting the potential risks to humans. Literature provides some information about the bioeffects of some NSAID solutions in low concentrations but there is no physicochemical explanation for these phenomena. Studying the physicochemical patterns of DS solutions in the low range of concentrations and establishing an interconnection between the solutions' physicochemical properties and bioeffects can provide a conceptually new and important source of information regarding the unknown effects of DS. The physicochemical properties and action of DS solutions on Ceriodaphnia affinis cladocerans, Paramecium caudatum infusoria, Chlorella vulgaris unicellular green algae, as well as on the growth of the roots of Triticum vulgare wheat seeds, were studied in the calculated concentration range of 1 × 10^-3-1 × 10^-18 mol/L. The relationship between these phenomena was established using the certified procedures for monitoring the toxicity of natural water and wastewater. It was shown for the first time that water solutions of DS are dispersed systems in which the dispersed phase undergoes a rearrangement with dilution, accompanied by changes in its size and properties, which affects the nonmonotonic dependences of the system's physicochemical properties and could cause nonmonotonic changes in action on hydrobionts in the low concentration range.