The physicochemical characteristics of the industrial effluent analyzed in the present study (Table 1) do not exceed the limits established in the official Mexican norms NOM-001-SEMARNAT-1996 and NOM-073-ECOL-1994. Dissolved oxygen was 12.2 mg L− 1, conductivity 143.2 μS cm− 1, ammonia 0.73 mg L− 1 and NaClO 1.0 mg L− 1; these PR619 four parameters are not considered in either of these norms.
According to Postma et al. (2002), ammonia and conductivity are confounding factors that may interfere with the bioeffects of micropollutants. The highest values at which the latter authors observed no significant effects were ammonia 13–60 mg L− 1 and conductivity < 650 μS cm− 1. On green algae basis, conductivity and ammonia in our study (143.2 μS cm− 1 and 0.73 mg L− 1 respectively) are not confounding factors.