ECOTOXICITY OF HOSPITAL WASTEWATER : USE OF CHLORIDES AS TRACERS OF THE TOXICITY OF POLLUTED SUBSTANCES ON DAPHNIA

摘要

Certain hospitals use in considerable quantities the hypochlorite of sodium and otheriodized substances to disinfect a volume of 750 liters of wastewater, which they produceon average by bed a day. Made before the implemented of the processes of settling ofsolid substances and filtration of the floating, this disinfection leads to an increase of theconcentration of organohalogen compounds (OHC) resulting from reactions of oxidereductionbetween the organic matter and the disinfectants. OHC are mostly lipophilic,persitent, and toxic. To evaluate the toxicity of industrial effluents, French water agencieshave developed a specific unit called “équitox/m~3” (which is equal to: 1/EC x 100 or 1/ICx 100). The application of the ecotoxicity tests Daphnia magna Strauss on hospitalwastewater samples, taken in an academic hospital center between February 22 andMarch 22, 2001, indicated a maximal acute toxicity of 116.8 équitox/m~3. This hightoxicity is due probably to the presence of organohalogen compounds. Besides, importantconcentrations in chlorides (359 mg/L) and in SSM (297 mg/L) are measured in theseeffluents. A specific conductivity of 1,67 mS/cm and a nearby pH of 8,0 were alsomeasured. This study aims to use the concentration obtained in chlorides in the hospitaleffluents for the first drawing of the acute toxicity of these wastewater. A linearregression is studied by means of the software XLSTAT, which gave an equation of theshape : Y = ?0 + X? + ε. A coefficient of correlation r=0,978 was found between theconcentration in chlorides and the results of the test of ecotoxicity on Daphnia. Theequation 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 similarmeasures on the other hospital effluents.