ECOTOXICITY OF HOSPITAL WASTEWATER : USE OF CHLORIDES AS TRACERS OF THE TOXICITY OF POLLUTED SUBSTANCES ON DAPHNIA
Abstract:Certain hospitals use in considerable quantities the hypochlorite of sodium and other iodized substances to disinfect a volume of 750 liters of wastewater, which they produce on average by bed a day. Made before the implemented of the processes of settling of solid substances and filtration of the floating, this disinfection leads to an increase of the concentration of organohalogen compounds (OHC) resulting from reactions of oxidereduction between the organic matter and the disinfectants. OHC are mostly lipophilic, persitent, and toxic. To evaluate the toxicity of industrial effluents, French water agencies have developed a specific unit called “équitox/m3” (which is equal to: 1/EC × 100 or 1/IC × 100). The application of the ecotoxicity tests Daphnia magna Strauss on hospital wastewater samples, taken in an academic hospital center between February 22 and March 22, 2001, indicated a maximal acute toxicity of 116.8 équitox/m3. This high toxicity is due probably to the presence of organohalogen compounds. Besides, important concentrations in chlorides (359 mg/L) and in SSM (297 mg/L) are measured in these effluents. A specific conductivity of 1,67 mS/cm and a nearby pH of 8,0 were also measured. This study aims to use the concentration obtained in chlorides in the hospital effluents for the first drawing of the acute toxicity of these wastewater. A linear regression is studied by means of the software XLSTAT, which gave an equation of the shape : Y = ß0 + Xß + å. A coefficient of correlation r=0,978 was found between the concentration in chlorides and the results of the test of ecotoxicity on Daphnia. The equation of the model is Y= −24,147 + 0,369X or equitox/m3 [Daphnia] = −24,147 + 0,369 [Cl−] mg/L. This work remains now to be validated by the realization of similar measures on the other hospital effluents.
Document Type: Research Article
Publication date: January 1, 2002
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