Phytotoxicity of Domestic Effluent Before and After Treatment by Stabilization Ponds

Abstract

Phytotoxicity tests linked to physicochemical parameters can be used to determine the possible effects of releasing a polluting load into the environment, evaluating the efficiency of a given treatment and its toxicity effects. In this context, the present work sought to evaluate the phytotoxicity of domestic effluent before and after treatment by stabilization ponds, using kale seeds (Brassica oleracea). Toxicity tests were carried out following the methodology of the American Environmental Protection Agency (EPA, 1996) at concentrations of 100%, 80%, 40%, 20%, 10%, and 5%. The seeds were incubated in a B.O.D. incubation chamber for five days at a temperature of 25ºC ± 2ºC. After this period, germination and root elongation were analyzed. The samples were also analyzed for biochemical oxygen demand, temperature, pH, turbidity, color, total solids, ammoniacal nitrogen, and organic nitrogen. Phytotoxicity was statistically evaluated by the Relative Growth Index, T-test (p < 0.05) for samples at 100% concentration, and Kruskal-Wallis followed by Dunn’s test (p < 0.05) to compare the negative control and the different concentrations. As a result, adverse effects of reduced root elongation were observed in samples of raw effluent (100%, 80%, and 20%) and treated effluent (10% and 5%), indicating a tendency toward phytotoxicity. Regarding the physicochemical parameters studied, all were within the established parameters by legislation, and no significant correlation was observed with root elongation. This may indicate the efficiency of stabilization ponds in treating domestic effluents, particularly in reducing phytotoxicity.