Toxicity of a glyphosate based formulation on phytoplanktonic green microalgae.

MAGDALENO A.; PÉREZ J.G.; JUÁREZ A.B.; RÍOS DE MOLINA M.C.

Roma

Otro; SETAC Europe 28th Annual Meeting; 2018

SETAC Europe

The emergence of transgenic crops led to an increase in the use of glyphosate and its presence in different ecosystems is a worldwide problem. Although it was designed to inhibit the aromatic amino acids synthesis in plants, glyphosate exerts toxic effects on non-target organisms, probably through other mechanisms. Its entry into waterbodies means a risk for biota, particularly for the phytoplankton microalgae community that sustains aquatic food webs. In this work the effects of a glyphosate formulation (≈44% monopotassium salt of N-phosphonomethyl glycine) on the growth, chlorophyll content and oxidative stress parameters of 4 phytoplanktonic green microalgae were evaluated. Cultures of Senedesmus acutus, Ankistrodesmus fusiformis, Monoraphidium contortum and Parachlorella kessleri were exposed to increasing glyphosate concentrations (0 ? 75 mg glyphosate/L) and kept at 24 ± 1 °C, under continuous agitation and illumination. After 96 h, growth, IC50, chlorophyll a content and oxidative stress parameters were evaluated. The glyphosate caused a significant decrease of chlorophyll a in M. contortum and P. kessleri, but not in the other two species tested. The growth of the 4 strains was negatively affected and regarding the IC50 values M. contortum was the mostsensitive strain (3.37 mg/L), followed by A. fusiformis (6.50 mg/L), S. acutus (14.74 mg/L) and P. kessleri (41.75 mg/L). In order to evaluate the relationship between antioxidant defenses and sensitivity, we analyzed parameters of oxidative stress in the least and the most sensitive strains. The exposition to 2-4 mg glyphosate/L in M. contortum and 30-75 mg glyphosate/L in P. kessleri, caused increases of reactive oxygen species, lipid peroxidation (TBARS), reduced glutathione, superoxide dismutase, and glutathione transferase. The level reached of TBARS in P kessleri was 10 times lower than in M. contortum, while the levels of antioxidant defenses were 3.5 - 7 times higher. These results suggest that oxidative stress would be involved in the toxicity of the glyphosate formulation and that the differences in sensitivity between strains could be due to differences in their defense antioxidant levels. According to the EU Directive 93/67/EEC, the IC50 values estimated indicate that the glyphosate formulation assayed should be toxic for aquatic biota. Besides, results also warn about its possible effects on the composition of phytoplankton, which would put at risk the balance of the aquatic ecosystem.