Sensitivity of Laboratory Test Organisms to Potassium Dichromate in Natural Water of the Moskva River

Abstract

Bioassay method was used to study the toxicity of natural water, sampled in the Moskva R. at sites with different level of anthropogenic impact in all hydrological seasons of the year. The effect of natural water chemistry on the sensitivity to a model toxicant (potassium dichromate) was evaluated for three laboratory test objects—unicellular algae Scenedesmus quadricauda (Turh.) Breb., crustaceans Daphnia magna Straus, and fish Poecilia reticulata Peters. The sensitivity of test objects was assessed by the values of median lethal (for daphnia and fish) and median effective (for algae) concentrations of the model toxicant, obtained with the use of the water samples as media for the preparation of test solutions of the toxicant. It was shown that, under the conditions of complex anthropogenic pollution, including an increase in TDS, the sensitivity of Daphnia magna and Poecilia reticulata to the standard toxicant was generally within the standard range for each test object, while in the case of Scenedesmus quadricauda, almost all obtained values of median effective concentrations were above the standard range (the sensitivity was lower). Statistically significant correlation was found between the median lethal concentration for Daphnia magna and a complex of interrelated hydrochemical characteristics, including TDS. The observed differences in the changes in the sensitivity of test-objects are presumably due to changes in water hardness. It is noted that the decrease in test object sensitivity under the effect of changes in water ionic composition can lead to overestimation of the maximal permissible concentrations, which are established with the use of natural water for water bodies, taking into account their natural features. The obtained results can be used in the formation of methodological approaches to regional standardization.