Resumen:
The quality of surface water is determined due to the physicochemical parameters and their compliance with the national regulation, these limits do not necessarily consider the accumulated effects of the contamination on the organisms and the aquatic ecosystem. The aim of this work is to demonstrate the need to include toxicity studies and biotic indicators as a complement to the physicochemical analysis taking as a case study the Cabeza de Toro ravine, in District 10 of the Municipality of Cercado in Tarija, Bolivia. Bioassays were performed using the Tox Track™ method, the inhibition of bacterial respirometric activity was determinate. Four of the six points tested showed a degree of inhibition within the expected, the inhibition degree of the municipal slaughterhouse effluent and the mixture of this with the effluent of the tanneries exceeds 100% of negative inhibition degree. In the germination test, the inhibition in seeds of Allium cepa in sediment samples was determinate, the level of toxicity was determined thru normalized germination index IGN, showing a very high toxicity level. The correlation of toxicity levels with the physicochemical parameters, exhibit a strong negative correlation between the iron concentration and toxicity. The biotic index could not be calculated, considering no organisms were found as described in the guide for the evaluation of benthic organisms.
