Acute toxicity of apple snailPomacea canaliculata’s eggs onRhinella arenarumtadpoles

Glyphosate affects the susceptibility of non-target native plant species according to their stage of development and degree of exposure in the landscape

Unsustainable agriculture is producing a great socio-ecological transformation in Latin America because it has expanded into areas occupied by native forests. Glyphosate is the most widely used herbicide, with severe ecotoxicological effects on non-target organisms. The aim of this study was to determine the effects of glyphosate on seedlings of 24 non-target herbaceous and non-herbaceous plant species present in forest relicts of Argentine Chaco. The effects of a gradient of glyphosate doses (525, 1050, 2100, 4200, and 8400 g ai/ha) were measured in seedlings of each species under greenhouse conditions. Seedlings were grown from seeds collected from native forest fragments of different sizes (assuming three different degrees of historical exposure to glyphosate in the landscape). Doses were applied at different stages of seedling development (five- and ten-weeks after emergence), and phytotoxicity, growth reduction, and sensitivity were measured. Glyphosate produced lethal or sublethal effects in all 24 species, some of which were very sensitive (>60 % of the species presented strong to severe growth reduction with ¼ of the dose used on crops). The greatest toxicological effects were related to early stage of development, herbaceous species, and low historical exposure to glyphosate. According to the species sensitivity distribution, the drift-dose to protect 95 % of the plant species that occur in larger forest fragments should not exceed 5 % of the dose commonly used on crops. These results suggest that the current weed management linked to glyphosate-resistant crops could lead to a gradual loss of biodiversity in the landscape. Concurrently, selection of glyphosate-tolerant biotypes in some non-target species could represent a very problematic cycle for the current model of industrial agriculture. Some alternatives for weed control are proposed.

Effects of the emulsifiable herbicide Dicamba on amphibian tadpoles: an underestimated toxicity risk?

The effects of exposure to the herbicide Dicamba (DIC) on tadpoles of two amphibian species, Scinax nasicus and Elachistocleis bicolor, were assessed. Mortality and biochemical sublethal effects were evaluated using acetylcholinesterase (AChE), glutathione S-transferase (GST), glutathione reductase (GR), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) activities and thyroid hormone (T4) levels. The LC₅₀ value at 48h was 0.859 mg L^-1 for S. nasicus and 0.221 mg L^-1 for E. bicolor tadpoles. After exposure to sublethal DIC concentrations for 48 h, GST activity increased in S. nasicus but significantly decreased in E. bicolor with respect to controls. GR activity decreased only in S. nasicus at all the tested DIC concentrations. AChE activity was significantly inhibited in both S. nasicus and E. bicolor tadpoles at 48 h. DIC also caused significant changes in transamination, as evidenced by an increase in AST and ALT activities in both amphibian species. T4 levels were higher in DIC-treated tadpoles of both species than in controls. The DIC-induced biochemical alterations in glutathione system enzymes and transaminases indicate lesions in liver tissues and cellular function. Moreover, the observed AChE inhibition could lead to the accumulation of acetylcholine, excessively stimulating postsynaptic receptors, and the increase in T4 levels in both species may indicate an overactive thyroid. The commercial DIC formulation showed a high biotoxicity in the two amphibian native species after short-term exposure, controversially differing from the toxicity level indicated in the official fact sheet data. This fact highlights the need for an urgent re-categorization and reevaluation of DIC toxicity in native species.