Estudios de ecotoxicidad sobre las lombrices Eisenia fetida de los fungicidas utilizados para el manejo de fusariosis del trigo

Commercial fungicides are composed of an active ingredient responsible for the direct and proven action that causes the death of the fungus, and ingredients declared as "inert". The latter, despite  their name may have effects on human health, environment and soil biota. However, for the entry of agrochemicals into Uruguay the tests required for fish and bees consider only the toxicity of the active ingredient as a reference. In addition, ecotoxicity tests on worms are not a requirement. Earthworms are a group of soil macrofauna that play a fundamental role in soil structure, chemistry and biology, reducing some fungal diseases, including wheat Fusarium wilt, through the elimination of the initial inoculum. Hence, the need  to evaluate which  toxic effects commercial formulations have on worms. The objectives of this work were to evaluate the chronic and reproductive effects of two commercial formulations (Prosaro and Swing Plus) on Eisenia fetida and the lethal or acute effects of the commercial fungicide Prosaro on Eisenia fetida. Four ecotoxicological bioassays were performed, two for reproduction and growth (TRC1 and TRC2) and two acute (TA1 and TA2), validated under the corresponding ISO standards and those described by Environment Canada (2007). All were performed in a controlled environment chamber at 20 ± 2°C, with a light/dark cycle of 16:8 h. for 56 days the CRT and 14 days the TA. For the reproduction and growth trials, 5 dilutions were used on a base 10 logarithmic scale, covering from one tenth of the field dose to the x103 field dose. Based on the preliminary results, a narrower range of concentrations of the commercial product used in the acute tests was determined. In the reproduction and growth bioassays, a stimulation in reproduction at low concentrations was seen for both formulations, showing a hormetic effect. No effects were observed on the biomass of the first generation at 56 days of the trial for a concentration equivalent to the field application dose. The lethal concentration values, LC50 (14 days) for Prosaro, obtained in the acute bioassays were (1790.48 mg kg-1 and 1116.67 mg kg-1 in TA1 and TA2 respectively) showed a greater toxicity of the formulation than that registered for the active ingredients in previous acute bioassays. This result contrasts with what was expected, since if we consider a summative effect of the LC50 of the active ingredients, a concentration of 2381 mg kg-1 of the formulation would have been needed to cause the death of 50% of the population. More studies are needed to evaluate the effects of commercial pesticides and their combinations, not only of their active ingredients separately, and also considering longer time scales. These tests allowed us to visualize the significant degree of uncertainty generated by the use of these products, with respect to the earthworm population but also to other soil animals. This effect should be considered in the risk assessment of chemical products, taking into account the direct and indirect contributions that earthworms make to biodiversity in soils, including contributions to human well-being, also called ecosystem services or functions.