Ecological risk analysis of pesticides used on irrigated rice crops in southern Brazil

Based on studies conducted in the past decade in the southern region of Brazil to determine residue levels of the pesticides normally used on irrigated rice crops, changes can be observed in relation to the presence of pesticides in the waters of the main river basins in Santa Catarina State. In previous harvests, the presence of residues of 7 pesticides was determined, with the herbicide bentazon and the insecticide carbofuran being the products showing highest frequency. Following toxicological tests conducted with 8 different test organisms, deterministic and probabilistic risk analysis was performed to assess the situation of the river basins in areas used for the production of irrigated rice. Of the species tested, the herbicide bentazon showed greatest toxicity toward plants, but did not present an ecological risk because in the worst-case scenario the highest concentration of this pesticide in the environment is 37 times lower than the lowest EC50/LC50 value obtained in the tests. The insecticide carbofuran, which had the highest toxicity toward the organisms used in the tests, presented an ecological risk in the deterministic analysis, but without any associated probability. The results highlight the need for increased efforts in training farmers in crop management practices and for the continual monitor of water bodies for the presence of pesticide residues.