ASSESSMENT OF TOXICITY OF RIVER WATER AND EFFLUENTS BY THE BIOLUMINESCENCE ASSAY USING PHOTOBACTERIUM-PHOSPHOREUM

The toxicity bioassay employing Photobacterium phosphoreum (LUMISTOX system) was used to evaluate the evolution of the quality of the River Tormes water during its passage through the city of Salamanca. To do so the toxicity of all the discharges into the river Tormes (22 total) were studied in the stretch in question, together with the impact of such discharges on the river course. Since pollution at low concentrations or the toxicity due to compounds that are strongly diluted in a fast flowing river may go undetected by the system,a technique of organic microcontaminant concentration using XAD-2 resins was used to detect different degrees of toxicity along the stretch studied. To a greater or lesser extent, all the discharges analyzed proved to be toxic for the photobacteria; the impact to the river caused by each was found to be a function of its EC50 and flow rate (Equitox/m(3)). The toxicity of the water of the river increases (the inhibition of luminescence (%H15), the dilution factor that inhibits luminescence by 20% (G120) and the concentration values leading to a 50% decrease in the emission of light (EC50) for an incubation time of 15 min, increase) as the river receives the different discharges, from the first sample (before the discharges studied), where the water concentrate has a low effective concentration 50 value (EC50 = 1.3) until the last sample (after the discharges studied), where the effective concentration 50 value is maximum (EC50 = 2.9).