EFFECTS OF THE HERBICIDE ROUNDUP® ON FRESHWATER MICROBIAL COMMUNITIES: A MESOCOSM STUDY

PÉREZ, G.; TORREMORELL, A.; MUGNI, H.; RODRÍGUEZ, PATRICIA; VERA, M. S.; DO NASCIMENTO, M.; ALLENDE, L.; BUSTINGORRY, J.; ESCARAY, R.; FERRARO, M.; IZAGUIRRE, I.; PIZARRO, H.; BONETTO, C.; MORRIS, D.; ZAGARESE, H.

ECOLOGICAL APPLICATIONS

The Ecological Society of America

Lugar: Washington, Estados Unidos; Año: 2007 vol. 17 p. 2310 - 2322

1051-0761

The impact of the widely used herbicide glyphosate has been mainly studied in terrestrial weed control, laboratory bioassays and field studies focusing on invertebrates, amphibians, and fishes. Despite the importance of phytoplankton and periphyton communities at the base of the aquatic food webs, fewer studies have investigated the effects of glyphosate on freshwater microbial assemblages. We assessed the effect of the commercial formulation Roundup® using artificial earthen mesocosms. The herbicide was added at three doses: a control (without Roundup®) and two treatments: 6 and 12 mg L-1 of the active ingredient (glyphosate). Estimates of the dissipation rate (k) were similar in the two treatments (half-lives of 5.77 and 7.37 d, respectively). The only two physicochemical parameters that resulted statistically significant were the vertical spectral attenuation coefficient [kd (ë)] and total phosphorus concentration (TP). At the end of the experiment, the treated mesocosms showed a significant increase in the ratio [kd (490 nm)/kd (550 nm)] and an eight-fold increase in TP. Roundup® affected the structure of phytoplankton and periphyton assemblages. Total micro- and nano-phytoplankton decreased in abundance in treated mesocosms. In contrast, the abundance of pico-cyanobacteria increased by a factor of about 40. Primary production also increased in treated mesocosms (roughly by a factor of 2). Similar patterns were observed in the periphytic assemblages, which showed increased proportion of dead / live individuals and increased abundances of cyanobacteria (about 4.5 fold). Interestingly, the observed changes in the microbial assemblages were captured by the analysis of the pigment composition of the phytoplankton, phytoplankton absorption spectra, and by the analysis of the optical properties of the water. The observed changes in the structure of the microbial assemblages are more consistent with a direct toxicological effect of glyphosate rather than to an indirect effect mediated by phosphorus enrichment.