Toxicity of a joint formulation of imazethapyr and glyphosate in Scenedesmus vacuolatus.

FASSIANO A.; MARCH H.; JUÁREZ A.B.; RÍOS DE MOLINA M.C

CABA

Congreso; 11th Biennial Meeting SETAC Latin America; 2015

SETAC LA

In recent years, to minimize the emergence of resistant weeds and to achieve a more sustainable control, herbicides mixtures have been developed. Many environmental factors can induce oxidative stress (OS). Particularly, the exposure to xenobiotics can trigger different OS processes, where reactive oxidative species (ROS) levels are increased, resulting in changes at the cellular level. The aim of this work is to analyze the participation of OS in the phytotoxicity of a mixed commercial formulation, OneWay®, containing imazethapyr 2% and glyphosate 24%, in Scenedesmus vacuolatus. This green microalgae was exposed to OneWay, concentrations corresponding to 0-6 mg imazethapyr/L, added to the medium, and BcoO (formulation mixture without active ingredients corresponding to the highest concentration of the tested formulation). Cultures were grown at 24±1ºC, under continuous light and agitation. After 96 hr, cultures were evaluated for cellular growth (EC50); gluthatione S-transferase activity (GST, a metabolic parameter), TBARS (a lipid peroxidation parameter) and pigment contents, antioxidant defenses (catalase -CAT- and superoxide dismutase -SOD- activities) and gluthatione levels (GSH, non-enzymatic antioxidant). Cell growth was significantly reduced from 4 mg imazethapyr/L, with a EC50 of 3.23 mg/L (IC95: 2.85-3.66). The chlorophyll a/ chlorophyll b, chlorophyll a/total chlorophyll and carotenes/chlorophyll a ratios did not vary significantly for any tested concentration or for the BcoO. The content of TBARS showed no significant variations in the concentrations tested. GST activity increased significantly at 4 mg/L, as well as in BcoO. GSH levels also increased significantly in a concentration dependent manner from 4 mg/L, as well as for BcoO. CAT activity presented a significant increase at 6 mg/L, while SOD activity did not vary significantly. The OneWay® formulation caused growth alterations in Scenedesmus vacuolatus. GST activity increased, indicating greater detoxifying activity, as well as GSH content and CAT activity, indicating a greater antioxidant protection. This would seem to mitigate the action of ROS and therefore no damage to lipids was observed and neither were modified pigment ratios. BcoO also caused metabolic changes in the microalgae, increasing the activity of the GST and GSH level. This would seem to mitigate the potential toxic effects of this component of the formulation since no alterations were observed in the microalgae growth.