Persistência na água e influência de herbicidas utilizados na lavoura arrozeira sobre a comunidade zooplanctônica de Cladocera, Copepoda e Rotifera

Abstract

Em lavoura de arroz irrigado, é utilizada uma grande quantidade de agroquímicos que, dependendo da sua persistência a campo e toxicidade, podem contaminar corpos d’água e afetar organismos vivos. Com o objetivo de determinar o efeito de concentrações de campo dos herbicidas Clomazone, Quinclorac, Metsulfuron-methyl e Propanil na comunidade zooplanctônica (Cladocera, Copepoda e Rotifera), conduziu-se um experimento em viveiros de aqüicultura, de março a maio de 2005, na estação do outono. Nos dias 1°, 2°, 3°, 7°, 10°, 18°, 31° e 51° após a aplicação dos herbicidas, foram coletadas amostras de água para se determinarem parâmetros físico-químicos da água, concentração dos herbicidas e comunidade zooplanctônica. Os parâmetros médios da qualidade da água foram: oxigênio dissolvido (3,5mg L-1), temperatura (20,1°C), pH (6,0), dureza total (18mg L-1 de CaCO3) e alcalinidade total (9mg L-1 de CaCO3). A ordem decrescente de persistência dos herbicidas na água foi Clomazone = Quinclorac > Propanil > Metsulfuron-methyl, com média de 31, 31, 10 e 7 dias, respectivamente. Os resultados indicaram que os herbicidas provocaram poucas alterações na densidade de organismos dos grupos Rotifera e Copepoda (Adulto e Nauplio). A densidade do grupo Cladocera permaneceu baixa para todo o período experimental.

The Impact of Herbicides on Benthic Organisms in Flooded Ricefields in Southern Brazil

“…This may have favored an increase in the abundance obtained in the last collection, since some taxa are sensitive to low levels of dissolved oxygen. The values of hardness and alkalinity were higher than in the present study compared to data from Golombieski et al (2008) and from Reimche et al (2008). A difference in the dissociation of ions of the compounds used in the experiments could explain this disparity.…”

“…The negative influence of this pesticide was perceptible in this study, since in both collections the treated plot had the lowest abundance and diversity of taxa compared to the other treatments. This possible influence was also recorded by Reimche et al (2008), where the cladoceran assemblage showed a density variation caused by the stress of the application of this herbicide. The use of pesticides reduces the availability of food for the benthic macroinvertebrates and changes the structure of the algae community, and the toxic effect on these food resources may also be associated with this (Gagneten, 2002).…”

“…All the herbicides except Quinclorac showed lower persistence than found in some studies (USEPA, 1996;Stevens et al, 1998;Mesléard et al, 2005;Mize et al, 2008;. However, Quinclorac was at least 2.5 times more persistent than observed by Reimche et al (2008). An evaluation of the persistence of pesticides in water of rivers in the region found that the compounds forming the commercial formulation Only (Imazapic + Imazethapyr) were present in all the sampling periods (Silva et al, 2009b).…”

“…Quinclorac showed a different dynamic than that studied in the laboratory by Crosby (2003), where it showed low persistence. In the study by Reimche et al (2008), this pesticide was detected until the 31st day, with its highest concentration observed on the 7th day with 102 µg.L -1 . In the present study, its persistence was higher than the other pesticides investigated, being detected until day 84 in a concentration of 3.8 µg.L -1 concentration.…”

Imazethapyr and imazapic, bispyribac-sodium and penoxsulam: Zooplankton and dissipation in subtropical rice paddy water

“…Triplicate samples were taken from each plot, comprising a 1000 mL final sample after mixing, stored into amber glass bottles and transported to laboratory. Samples were analyzed for imazethapyr according to Santos et al (2008), imazapic by Reimche et al (2008), bispyribac-sodium by Kurz (2009) and penoxsulam by Zanella et al (2003), using High Performance Liquid Chromatography with Diode Array Detection (HPLC-DAD) with a Varian system (Palo Alto, CA, USA) composed of ProStar 210 pump and ProStar 335 DAD detector. The column configuration consisted of a Phenomenex (USA) C-18 reversed-phase column (250 × 4.6 mm; 5 μm) and a Phenomenex C-18 guard column (10 × 4.6 mm; 5 μm).…”