Qualidade da água do Rio Vacacaí, São Sabriel, RS

Abstract

Being responsible for waterborne diseases, the bacteria from the coliform group are used as sign of fecal contamination. The objective of this work was to estimate the most probable number (MPN) of total coliforms (TC) and fecal coliforms (FC) in the Vacacaí river and its tributary "Sanga da Bica”, São Gabriel, RS; to verify the water quality and determine the probable of sources of contamination. Two places in “Sanga da Bica” ("A" and "B") and one place in the river ("C") were chosen for sampling. The places were monthly sampled from May to October 2009. In order to define whether the river can be used for recreation, three places were defined ("D", "E" and "F") for the analysis of water quality. The sources of contamination were measured by using the runoff water from a field near the river where waste from a frigorific is dumped ("S1", "S2" and "S3"). In the point "A" the MPN of total coliforms and fecal coliforms per 100 ml of water was 16,000 during all months analyzed. The point "B" presented 16,000 total coliforms during May, June, July and October and 3,000 during August and September. In May and September the MPN of fecal coliforms per 100 ml was 9,000 while in June and July the number of fecal coliforms per 100 ml was 16,000. During August and October the MPN of fecal and total coliforms per 100 ml of water was 3,000 and 5,000, respectively. In May the MPN of total and fecal coliforms in the sampling point "C" was 16,000. In June, the MPN of total coliforms per 100 ml of water was 800 and the number of fecal coliforms was 90. In July the MPN of total coliforms was 5,000 and the number of fecal coliforms was 1,300. In August, September and October the MPN of fecal coliforms per 100 ml of water was 3,000 and the number of total coliforms was 5,000. In the sampling point "D" MPN of fecal coliforrms per 100 ml of water was 16,000 and the MPN of total coliforms was 5,000. In the sampling point "E" the MPN of total coliforms per 100 mL of water was 3,000 and the number of fecal coliforms was 2,400. In the sampling point "F" MPN of total coliforrms was 2,800 and the number of fecal coliforms was 1,400. The water was determined to be inadequate for recreation purposes and other uses in the sampling points "A", "B" and "D". In the point "C" the water was only considered adequate for recreation and other uses during June. The water sampled in the points "E" and "F" were suitable for recreation and unsuitable for other uses. The total and fecal coliforms can persist in the soil and due to the precipitation; soil particles can be focus of contamination due the presence of pathogens offering risks to the public health. The domestic effluents can be considered sources of fecal contamination in the Vacacaí river and its tributary.