Toxicity of 2,4-d herbicide: scientometric review and cronic bioassay in rhamdia quelen (siluriformes: heptapteridae)

Abstract

In the present study, it was sought at first to assess the current state of studies on the toxicity of 2,4-D. For the scientometric review, the data available on the Web of Science (WoS) were used to provide information on the specific toxicity and mutagenicity characteristics of 2,4-D. It was found that the USA was the most active collaborator with the highest publication and centrality (importance). The 2,4-D research was strongly related to the keywords glyphosate, atrazine, water and gene expression. The studies tended to focus on occupational risk, neurotoxicity, resistance or tolerance to herbicides and non-target species and molecular impression. Future research on 2,4-D toxicology and mutagenicity is likely to focus on gene expression, assessment of exposure in humans or other vertebrate bioindicators and studies of pesticide degradation. This scientometric analysis allowed us to make inferences about global trends in toxicology and 2,4-D mutagenicity, thus contributing to future research efforts. In addition, the effect of 2,4-D doses on Rhamdia quelen was evaluated in a subchronic bioassay; in this case, we opted for the trophic route of exposure and the investigation of biomarkers in liver, gonads and blood. For the bioassay, four test doses of the herbicide 2,4-D were determined: 0µg.kg-1 (control), 20µg.kg-1, 200µg.kg-1, 2000µg.kg1. The specimens were randomly distributed in nurseries belonging to four nurseries (tanks). The four nurseries per nursery corresponded to the four concentrations of 2,4-D studied. The exposure periods were 22 and 42 days. Doses were administered to the animals every 10 days with the aid of gavage needles. The parameters analyzed were: somatic indexes, histopathologies of liver and gonads and detection of vitellogenin. The histopathological analysis of the liver showed: cytoplasmic vacuolization, free macrophages, vacuolar degeneration, lipocytes, melanomacrophage center, pancreatic tissue hyperplasia, necrosis and inflammation. The liver also showed a higher frequency of damage at the two highest doses of 2,4-D. In female gonads, damage was concentrated in the lowest dose, with increased atresia and decreased vitelogenesis. In males, the damage was significantly greater in groups treated with 2,4-D, in all doses, leading from asynchronous development and increased sperm count to hermaphroditism. In qualitative analyzes of vitellogenin, it was observed that 2,4-D increased the expression of this protein in females and also induced the production of this protein in treated males. It is concluded that 2,4-D has a toxic effect on R. quelen, being a potential endocrine disruptor for the species.