Abstract
Salinity limits the habitable living environment for aquatic organisms. Algae and crustaceans are widely used as bioindicators in freshwater environmental risk assessments. This study aimed to use biotests (Algaltoxkit and Daphtoxkit) to determine the effect of sodium chloride (NaCl) on algae Pseudokirchneriella subcapitata and crustaceans Daphnia magna. Standard biotests were extended to include NaCl effects on algal chlorophyll fluorescence and crustaceans swimming and heart rate. It was found that after 7 days, a 0.24 M of NaCl reduced the growth rate of the algae by 50% (EC50). A NaCl of 0.27 M inhibited the minimum (Fo), maximum (Fm) and variable (Fv) fluorescence by 50%, on average. The crustaceans also responded to NaCl. Those exposed to 0.19 M NaCl during 15 min swam slower by 50% and a 0.27 M immobilised three organisms (EC50). The crustacean immobilisation was less modified by NaCl than swimming. To determine the lethal effect in non-swimming organisms, the heart rate was examined. At 0.35 M of NaCl, all organisms were dead after 30 min, as their hearts did not beat. These studies suggest that physiological and behavioural features are sensitive indicators of the toxic effects of NaCl in algae and crustaceans, before morphological changes are observed.
Highlights
Water is one of the most important environmental resources and the availability of good quality water determines the life of organisms
This study aimed to determine the effects of the exposure of algae P. subcapitata and crustaceans D. magna—neighbouring freshwater links of the food chain to sodium chloride at different concentrations, to determine the adverse effects when water is contaminated with this salt
Five and seven days of the experiment, it was demonstrated that increasing sodium chloride concentrations and time modified the Y of algae P. subcapitata (Table 1)
Summary
Water is one of the most important environmental resources and the availability of good quality water determines the life of organisms. Chloride enters waters with discharges of contaminated post-mining water to the aquatic environment, and with surface run-off from urbanised areas, where it is used for the de-icing of roads. As sodium chloride is a cheap and readily available raw material, it is widely used on roads [3]. After such application, 40–77% of salt is retained in the environment throughout the growing season [4,5,6]. The food industry, including the dairy, fish and meat sectors, generate high-strength wastewater with an admittedly variable, but short-term, high salt concentration (3.3 g × L−1 of sodium chloride), as a result of use of this salt for the disinfection of equipment and food processing in factories [8]. Sodium chloride is used in commercial aquaculture as a drug to control pathogenic microorganisms by immersing fish in NaCl solutions at concentrations ranging from 0.015 to 35.0 g × L−1 [9]
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