Water quality assessment by ecotoxicological and limnological methods in water supplies, southeast Brazil.

The quality of the water supplied to Araraquara city (São Paulo State, Brazil) was analyzed at four points: two reservoirs from which water is pumped and the water incoming and exiting a drinking-water treatment plant. Physical and chemical analyses of water were performed, as well as acute and chronic toxicity tests of the water from all four points, using Ceriodaphnia silvestrii (Cladocera, Crustacea) as test-organism. The study was carried out monthly in the period between December 2000 and November 2001. Water from the reservoirs caused neither acute nor chronic toxicity to test-organisms. On the contrary, it promoted an increase in the fecundity of cladocerans compared to control, suggesting greater availability of food. However, the water from exiting the treatment plant did cause chronic toxicity to C. silvestrii, regarding both fecundity and mortality. The toxicity was probably caused by residual chlorine, perhaps not completely removed by aeration, or by chlorine disinfection by-products (trihalomethanes) in the treated water, considering the level of organic matter present in the reservoir water.