Acute toxicity of pyrazosulfuron-ethyl and permethrin to juvenile Litopenaeus vannamei =Toxicidade aguda de pirazossulfurom-etílico e permethrin em juvenis de camarão branco Litopenaeus vannamei

Abstract

The objective of this study was to determine the LC50 (96h) of two pesticides: SiriusR 250 SC herbicide of the pyrazosulfuron-ethyl group, and TalcordR insecticide of the permethrin group, on juvenile Litopenaeus vannamei. Shrimp total hemocyte count (THC) was also determined as an indication of physiological alterations caused by the pesticides. Juvenile shrimp (5.0 } 0.5 g) were exposed to the following concentrations: 0, 0.1, 1.0, 10, 100 and 1000 ƒÊg L-1 SiriusR 250 SC; and 0, 0.001, 0.01, 0.1, 1.0 and 10 ƒÊg L-1 TalcordR. The TalcordR LC50 (96h) was of 0.00933 ƒÊg L-1 or 9.33 ng L-1. There were no significant changes in the THC between control and test groups. No SiriusR 250 SC concentrations tested killed more than 50%of the shrimp; therefore, the herbicide was considered not toxic to the juveniles. However, the THC showed significant differences between the control and test groups, suggesting sublethal effects to L. vannamei juveniles. According to the results, the insecticide TalcordR is highly lethal for L. vannamei and the herbicide SiriusR 250 SC was not lethal in the concentrations tested but showed sublethal effects as lower THC. The results demonstrate the risks involved in farming L. vannamei shrimp near rice cultures where these pesticides are routinely used.O objetivo deste trabalho foi determinar a CL50 (96h) dos agroquimicos SiriusR 250 SC, herbicida a base de pirazossulfurom-etilico, e TalcordR, inseticida a base de permethrin, em juvenis de Litopenaeus vannamei, bem como avaliar possiveis alteracoes fisiologicas por meio da contagem total de hemocitos (CTH) dos camaroes. Juvenis de L. vannamei (5,0 } 0,5 g) foram expostos as seguintes concentracoes dos agroquimicos: SiriusR 250 SC, 0; 0,1; 1; 10; 100 e 1.000 ƒÊg L-1, e TalcordR, 0; 0,001; 0,01; 0,1; 1 e 10 ƒÊg L-1. A CL50 (96h) do inseticida TalcordR foi de 0,00933 ƒÊg L-1 ou 9,33 ng L-1. Nao houve alteracoes significativas da CTH entre as medias dos grupos-controle e dos submetidos ao inseticida. Combase nas concentracoes testadas do herbicida SiriusR 250 SC, nao foi possivel determinar a CL50 (96h), assim, este produto nao foi considerado toxico para os juvenis de L. vannamei. Porem, a CTH dos camaroes expostos ao herbicida demonstrou diferencas significativas entre as medias do controle e dos tratamentos, o que evidenciou efeito subletal. Os resultados permitem concluir que o inseticida TalcordR e altamente letal para os juvenis de L. vannamei e o herbicida SiriusR 250 SC, apesar de nao ter a mesma toxicidade, apresenta efeito subletal relacionado com a diminuicao na CTH. Os resultados sugerem a existencia de riscos em se cultivar L. vannamei nas proximidades de fazendas de arroz, em que defensivos agricolas sao usados rotineiramente.

Keywords

• toxicology
• pesticides
• shrimp culture
• Litopenaeus vannamei
• toxicologia
• pesticidas
• carcinicultura