RESUMEN
The toxicity of the ixodicidal carbamates ethyl-4-bromophenyl carbamate (LQM 919), ethyl-4-chlorophenyl carbamate (LQM 996) and propoxur on Eisenia foetida adults was evaluated to estimate their ecotoxic potential. The earthworm mortality and weight loss produced by the three evaluated carbamates showed a concentration-dependent effect (pâ¯<â¯0.0001) in the contact filter paper test (CFPT). In the artificial soil test (AST), mortality increased in relation to the exposure time (pâ¯<â¯0.0001) and the concentration (pâ¯<â¯0.01) of the carbamates. Only the earthworms exposed in the CFPT showed morphological alterations. According to the LC50 obtained in the CFPT, the three carbamates were classified as very toxic and, according to the LC50 obtained in the AST, the three carbamates were classified as highly toxic for E. foetida. The values of ki and kd indicated that LQM 919 and LQM 996 are weak inhibitors with lower affinity for the acetylcholinesterase of E. foetida than that of propoxur. The concentrations in the CFPT and AST at which 100% mortality was observed in E. foetida were 64- and 4-fold higher, respectively, than the egg hatching inhibitory concentration 99% reported for ticks.
Asunto(s)
Acetilcolinesterasa/metabolismo , Carbamatos/toxicidad , Oligoquetos/efectos de los fármacos , Propoxur/toxicidad , Contaminantes del Suelo/toxicidad , Animales , Dosificación Letal Mediana , Oligoquetos/enzimología , Suelo/químicaRESUMEN
The effects produced by the ethyl-carbamates: ethyl-4-bromophenyl carbamate (LQM 919) and ethyl-4-chlorophenyl carbamate (LQM 996) on the mortality and behavior of Apis mellifera were evaluated by the acute oral toxicity test and the acute contact toxicity test. The oral lethal dose, 50% of the ethyl-carbamates was >145.24⯵g per bee, and the oral lethal dose, 50% of propoxur was 0.072⯵g per bee. Therefore, according to the OECD criteria, the ethyl-carbamates were classified as relatively nontoxic orally; meanwhile, propoxur was classified as highly toxic orally. In the contact test, lethal concentrations 50% of the ethyl-carbamates were 4.83 and 2.23⯵g/cm2 for LQM 919 and LQM 996, respectively; therefore, they were at least 10-fold less lethal (pâ¯<â¯0.05) than propoxur (0.22⯵g/cm2). The ethyl-carbamates reduced the activity of A. mellifera acetylcholinesterase by up to 30%. The ki and kd values of both ethyl-carbamates were lower (pâ¯<â¯0.05) than those of propoxur and indicated that they are weak inhibitors and with low affinity to A. mellifera acetylcholinesterase, which along with the absence of behavioral alterations suggests that the mortality caused by ethyl carbamates is not related to damage to the nervous system. According to these results, the evaluated ethyl-carbamates can be considered a low ecotoxic risk for A. mellifera.
Asunto(s)
Acetilcolinesterasa/metabolismo , Abejas/efectos de los fármacos , Carbamatos/toxicidad , Contaminantes Ambientales/toxicidad , Insecticidas/toxicidad , Animales , Abejas/enzimología , Conducta Animal/efectos de los fármacos , Exposición Dietética/efectos adversos , Exposición a Riesgos Ambientales/efectos adversos , Dosificación Letal Mediana , Pruebas de Toxicidad AgudaRESUMEN
The purpose of this work was to contribute to the understanding of the mechanism of action of two new ixodicides. The histological and ultrastructural alterations of Rhipicephalus microplus oocytes (San Alfonso strain) treated with two new ethyl-carbamates (ethyl-4-bromophenyl carbamate and ethyl-4-chlorophenyl carbamate) by the adult immersion test were evaluated by light microscopy and transmission electron microscopy. The effects of the carbamates on embryogenesis in eggs were evaluated by fluorescence microscopy using DAPI staining. Both ethyl-carbamates inhibited the maturation of most oocytes and induced a concentration-dependent decrease (r2⯠=â¯0.5, pâ¯<â¯0.05) in the embryonation percentage in the small number of eggs oviposited by treated ticks. Evident ultrastructural alterations were observed in the oocytes from ticks exposed to the ethyl-carbamates, including modification of the chorion structure, myelinic bodies and autophagic vacuoles that were associated with degenerated organelles (mitochondria, endoplasmic reticulum and yolk granules), nucleolus fragmentation and chromatin clumping in germinal vesicles. In conclusion, these ethyl-carbamates affect the reproductive potential of R. microplus due to their negative effects on oogenesis and their repercussions for embryonic development.
Asunto(s)
Acaricidas , Carbamatos , Rhipicephalus , Control de Ácaros y Garrapatas , Animales , Embrión no Mamífero/efectos de los fármacos , Desarrollo Embrionario/efectos de los fármacos , Microscopía , Microscopía Electrónica de Transmisión , Microscopía Fluorescente , Oocitos , Oogénesis/efectos de los fármacos , Óvulo/efectos de los fármacos , Rhipicephalus/embriología , Rhipicephalus/crecimiento & desarrolloRESUMEN
Ethyl-4-bromophenyl-carbamate (LQM 919) and Ethyl-4-chlorophenyl-carbamate (LQM 996) are compounds that inhibit egg-laying and hatching of tick larvae that are resistant to conventional ixodicides. The structure-activity relationship (SAR) to get the endpoint predictions of mutagenicity and carcinogenicity of the LQM 919 and LQM 996 was performed and the absence of mutagenicity was confirmed by Ames test. SAR analysis show no structural alerts indicating the ability of ethyl-carbamates to bind biomolecules or estrogen receptors. Endpoint of mutagenicity with and without metabolic activation showed that the ethyl-carbamates were negative (p <0.05) for mutagenicity induction in strains TA97, TA98, TA102, TA1535, TA1537 and TA1538 of Salmonella typhimurium. Pre-incubation with different ethyl-carbamate concentrations did not increase the number of spontaneously reverting colonies; moreover, the compounds did not induce a concentration-dependent increase in the number of reverting colonies in any of the strains used. This confirmed the absence of mutagenic activity in this test system. Exogenous metabolic activation did not modify these observations; suggesting that no metabolites with mutagenic activity were present. The endpoint of carcinogenicity in rats were negative for LQM 919 (p <0.05,) and LQM 996 (p <0.001). The results of the present study strongly suggest that ethyl-carbamates do not represent a risk for cancer in mammals.