Abstract
Glyphosate is the worldwide used herbicide of the first priority. However, its biochemical effects in the aquatic animals are studied scantly. The ex vivo approach has been recently proposed to provide the express evaluation of the adverse impact without the treating of the organisms. The aim of this study was to verify this approach for the assessment of the toxicity of glyphosate to the bivalve mollusk. The samples of the gills and digestive gland tissues of freshwater bivalve Unio tumidus mollusk were exposed to a range of the concentrations of glyphosate (commercial formulation Roundup MAX) at the concentrations 13.3, 26.7, 66.8 and 133.6 µg×L -1 during 2 h at 20 °C followed by 15 h at ~ 2–4 o C. The markers of oxidative injury (total antioxidant activity, end-products of lipid peroxidation (TBARS) and protein carbonyls (PC)), cellular low weight thiols GSH/GSSG and metallothionein (MT), and cholinesterase activity as the index of neurotoxicity were analyzed. We also assayed the index of cell vitality as the lysosomal membrane stability from the Neutral Red Retention (NRR) test. The results have shown that the lowest concentrations of glyphosate caused the most prominent changes of the indices: the decrease of MT concentration (by ~ two times) and cholinesterase activity. The total antioxidant activity was decreased substantially in all exposures correspondingly to a decrease of the MT and/or GSH concentrations. However, the levels of TBARS and PC were not changed comparing to control detecting the early stage of the injury. Surprisingly, NRR increased in the exposures to higher concentrations of glyphosate, probably due to strong chelating ability of glyphosate or other compounds of formulation. This study allows us to detect the earlier biological effects of glyphosate in the low environmentally realistic concentrations. Further validation of this approach needs the comparison of the results in the ex vivo and in vivo experiments. Keywords: Roundup; bivalve mollusk; cytotoxicity; ex vivo
Highlights
Glyphosate (Gl), the modified aminoacid and the organophosphonate compound, N-(phosphonomethyl)glycine, is the most sprayed and most used herbicide in the world [4; 19]
The strong chelating properties were found for Gl, that cause the immobilization of mineral nutrients by the organisms
According to environmental quality standards of Brazilia, the maximum value allowed for Class I waters for glyphosate is 65 μg/L [17]
Summary
Glyphosate (Gl), the modified aminoacid and the organophosphonate compound, N-(phosphonomethyl)glycine, is the most sprayed and most used herbicide in the world [4; 19]. Whereas it acts as the specific inhibitor of the enzyme 5-enolpyruvylshikimate3-phosphate synthase intrinsic for the plant and bacteria, blocking the synthesis of aromatic compounds, it was originally marketed as absolutely non-toxic for the animals [26]. Its by-side effect on the non-targeted organisms were reported later: the loss of the immune defense of the animals and human due to the impact on the symbiotic microorganisms [25]. The biochemical responses that serve for the early warning of ecotoxicity, are less known [18]
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