Efectos de metales pesados, glifosato y sus mezclas binarias sobre el crecimiento de algas verdes

Abstract

Rivers and streams of rural areas of the Buenos Aires Province contain variable concentrations of heavy metals and glyphosate. In this study, the toxicity of the metals Cu, Pb and Zn, the herbicide glyphosate (active product and ATANOR® formulation) and their binary combinations, was assessed on two green algae species (the standard species Raphidocelis subcapitata and a native strain of Scenedesmus acutus isolated from Burgos Stream [Buenos Aires]). The bioassays were carried out applying a concentration range of 0.5 mg/L - 20 mg/L, in incubations lasting 7 days after which the algal density was estimated. To obtain the effective concentrations inhibiting 10, 20 and 50% of the growth (EC10, EC20 and EC50) of individual substances and their combinations, the percentage of growth inhibition (%I) was modeled as a function of each concentration by a nonlinear fit. According to the EC50 obtained for each species, the toxicity of Cu and Zn was higher in R. subcapitata (7.47±2.14 and 6.51±2.26 mg/L, respectively) than in S. acutus (10.90±3.75 and> 20 mg/L), while Pb and glyphosate active compound were not toxic for neither of the two strains. ATANOR® glyphosate was toxic only to R. subcapitata (EC50=12.00±3.10 mg/L). According to the EC10 and EC20 values of the individual substances and the binary combinations, S. acutus showed higher sensitivity than R. subcapitata. From the analysis of toxic units (TU), the combinations Cu+Zn, Cu+glyphosate ATANOR® and Zn+glyphosate ATANOR® showed antagonistic effects on R. subcapitata (according to the TU values obtained from EC20 and EC50), while the Cu+Pb and Cu+Zn combinations showed synergistic and antagonistic effects, respectively, on S. acutus (according to the TU values obtained from the EC20). These results highlight the importance of conducting bioassays of toxic substances using native algal strains which allow inferring potential effects in native communities and food webs.