Efeito Dos Herbicidas Imazapir E Imazapique Na Comunidade Fitoplanctônica Em Lavoura De Arroz Irrigado

Abstract

RESUMO -Diante da toxicidade de herbicidas aos organismos aquáticos, comumente utilizados em lavouras de arroz irrigado, o presente trabalho visou avaliar o efeito toxicológico da mistura herbicida imazapir+imazapique (Kifi x ® ) e compostos isolados na comunidade fi toplanctônica utilizando mesocosmos. Os efeitos destes contaminantes foram avaliados por delineamento experimental em blocos ao acaso com esquema fatorial (5 x 3) e quatro repetições, totalizando 16 parcelas amostrais. Este estudo demonstrou pela Principal Curva de Resposta (PRC) que os herbicidas imazapir+imazapique (Kifi x ® ), imazapir e imazapique proporcionam efeito sobre a abundância e composição do fi toplâncton. Os maiores efeitos dos herbicidas em estudo foram encontrados sobre táxons pertencentes às classes Cyanophyceae, Chlamydophyceae e Chlorophyceae. Os tratamentos com herbicidas assemelharam-se ao controle na última coleta, constatando que os herbicidas são mais tóxicos nos primeiros dias após a aplicação. Palavras-chave: algas, imidazolinonas, mesocosmos, Oryza sativaABSTRACT -Eff ect of herbicides imazapyr and imazapicon in the phytoplanktonic community of rice paddy fi elds. Considering the toxicity of herbicides commonly used in irrigated rice fi elds to aquatic organisms, this study aimed to assess the toxic eff ects of the mixture imazapyr+imazapic (Kifi x®), and also of the isolated compounds on the phytoplankton community using experiments in mesocosms. The eff ects of these contaminants were examined through experimental design with random blocks (5 x 3) and four repetitions, totaling in 16 sampling units. Using a principal response curves analysis (PRC), the experiment demonstrated that the compound imazapyr + imazapic (Kifi x®), and the single products imazapyr and imazapic have strong eff ects on the composition and abundance of phytoplankton communities. The greatest eff ects were found on three classes of microalgae Cyanophyceae, Chlamydophyceae and Chlorophyceae. The communities treated with the herbicides closely resembled the control blocks on the last sampling day, showing that the toxic eff ects are more pronounced within the fi rst days of application.

Do phytoplankton and epiphyton communities differ between organic and conventional rice fields?

“…In mesocosms, however, greater values of phytoplankton community richness were found in rice cultivated without the spraying of pesticides but with residual imidazolinone (151 species), such as in rice cultivated with imazapyr and imazapic herbicides (60 genera, with 44 genera observed by us), according to Cassol et al (2013) and Reck et al (2018), respectively. Baert et al (2016) exposed the plankton diatom community at different levels of richness to different concentrations of atrazine herbicide and observed that more diverse communities were less affected by herbicide stress.…”

“…In the CF, the values of pH and dissolved oxygen were close to the ones registered in the Ibirapuitã River (7.1 -9.1 and 7.02 -9.06 mg L -1 , respectively) in 2018, according to the ANA (2018). The water pH ranging from slightly acidic to neutral from the CF is similar to that of mesocosms that underwent herbicide spraying and the control treatment (Reck et al 2018;Reimche et al 2015).…”

“…Faster recovery events observed in other studies, associated with the phytoplankton being subjected to the water flow, can hinder the detection of punctual impacts because the evaluation was not done 24 h after herbicide spraying. Imazapyr and imazapic herbicides, whose mechanism of action is the same as that of penoxsulam, inhibited the growth of the phytoplankton community 24 h after the spraying in mesocosms (Reck et al 2018). Residual water from CF after spraying with herbicides, such as clomazone, inhibited the growth of Chlorella vulgaris, Pseudokirchneriella subcapitata, and Desmodesmus subcapitatus strains 2 days after spraying (Suárez-Serrano et al 2010).…”

“…Radiococcus planktonicus, an indicator species of organic farming, has cells that are enveloped by a mucilaginous sheath making it easy to float. It has been suggested that colonial genera such as Aphanocapsa, Eudorina, Pandorina, and Sphaerocystis are sensitive to the presence of imazapyr and imazapic herbicides belonging to the penoxsulam chemical group in rice farming mesocosms (Reck et al 2018). The low abundance of green algae in CF and their predominance in OF suggest the effects that herbicide sprays have on the environment.…”

“…However, there is no field comparative information about algal communities in organic and conventional rice farming with herbicide application. Furthermore, the effects of herbicides on epiphytic and planktonic algae in paddy rice fields have been described mainly in mesocosms (Sartori et al 2011;Cassol et al 2013;Reck et al 2018;Liu et al 2020). This knowledge gap motivated us to investigate the phytoplankton and epiphyton in the two rice cultivation systems.…”