Influência da temperatura na toxicidade dos herbicidas sulfentrazone (Boral 500SC®) e clomazone (Gamit®) em larvas de anuros Eupemphix nattereri (Leiuperidae) e Rhinella schneideri (Bufonidae)
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Data
2017-03-17
Autores
Freitas, Juliane Silberschmidt [UNESP]
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Universidade Estadual Paulista (Unesp)
Resumo
A temperatura é um importante fator ambiental influenciando o metabolismo, desenvolvimento e comportamento de animais de sangue frio. Entretanto, os efeitos indiretos da temperatura em sistemas naturais, tais como o potencial de interação com contaminantes ambientais, ainda são pouco estudados para muitos táxons. As alterações nos padrões de temperatura podem potencialmente alterar a natureza e distribuição de muitos contaminantes no ambiente e, por isso, o maior desafio atual dos ecotoxicologistas está em prever os riscos estabelecidos por essas interações a nível biológico. Os agrotóxicos incluem o principal grupo de agentes tóxicos encontrados em sistemas naturais, sendo grande parte desses compostos provenientes da manutenção de culturas de cana-de-açúcar no controle de plantas invasoras no Brasil. No noroeste paulista do país, muitas espécies de anuros estão distribuídas em áreas comuns à agricultura, com ocorrência reprodutiva restrita à estação chuvosa, a qual coincide com o período de maior contaminação ambiental. O presente trabalho objetivou avaliar a influência da temperatura na toxicidade dos herbicidas sulfentrazone, clomazone e diuron em larvas de anuros, utilizando biomarcadores fisiológicos, bioquímicos e moleculares específicos. O primeiro estudo investigou os efeitos dos herbicidas sulfentrazone (Boral SC500C®) e clomazone (Gamit®) em girinos de Eupemphix nattereri e Rhinella schneideri submetidos a diferentes condições térmicas (28, 32 e 36 ºC) através da análise das respostas antioxidantes e de peroxidação lipídica. Em um segundo trabalho, objetivamos investigar os potenciais efeitos endócrinos do herbicida diuron e seu metabólito (3,4-DCA) (40 e 200ng/L) em girinos de Lithobates catesbeianus submetidos a condições de estresse térmico (28 e 34 ºC), utilizando para isso biomarcadores moleculares e enzimáticos relacionados à atividade da tireoide em anfíbios. Os resultados mostraram que a temperatura foi um importante fator influenciando a toxicidade dos herbicidas em estudo para as diferentes espécies de girinos. Além disso, alterações dos diferentes biomarcadores também foram mediadas pelo efeito isolado da temperatura. A exposição de girinos de E. nattereri e R. schneideri aos herbicidas clomazone e sulfentrazone provocou alterações na atividade das enzimas antioxidantes, além de aumentos nos níveis de malondialdeido (MDA), indicando ocorrência de estresse oxidativo; entretanto, essas respostas foram diretamente relacionadas às temperaturas de exposição para ambas as espécies. A maioria das enzimas apresentou atividades pronunciadas em temperaturas mais elevadas e em combinação à presença dos contaminantes. Esses dados são provavelmente devido ao aumento da toxicidade de contaminantes em temperaturas mais elevadas como resultado de um incremento das taxas metabólicas desses animais de sangue frio. Os diferentes mecanismos de ativação do sistema antioxidante em E. nattereri e R. schneideri também sugere que girinos de regiões tropicais devem utilizar diferentes estratégias e mecanismos de adaptação para lidar com os efeitos gerados pela exposição a agrotóxicos em habitats onde a temperatura é um fator de influência relevante. Nos resultados de nosso segundo trabalho, encontramos que o herbicida diuron e seu metabólito 3,4-DCA são potentes desreguladores da tireoide em girinos de L. catesbeianus, entretanto esses efeitos endócrinos são pronunciados em temperaturas mais elevadas. Além de indução na expressão de genes relacionados ao processo de metamorfose, observamos alterações nos níveis plasmáticos de triiodotironina (T3) e uma aceleração na metamorfose de animais expostos à condição combinada de temperatura elevada em presença aos contaminantes, diuron ou 3,4-DCA. De forma geral, nossos resultados sugerem que condições realísticas de temperatura ambiental deveriam ser levadas cada vez mais em consideração em estudos de risco avaliando a exposição de anfíbios a contaminantes ambientais, tais como agrotóxicos. A falta de abordagem dessas variáveis em testes laboratoriais pode levar a interpretações subestimadas relacionadas aos efeitos tóxicos desses compostos em diferentes espécies de anfíbios.
Temperature is an important environmental factor influencing the metabolism, development and behavior of cold-blooded animals. However, indirect effects of temperature on natural systems, such as the potential of interaction with environmental contaminants have not been well-characterized for many taxa. Changes in temperature patterns can potentially alter the nature and distribution of many contaminants in the environment, and therefore the current challenge for ecotoxicologists is to predict the risks established by these interactions at biological level. Pesticides are the main group of toxicants present in natural systems and a large part of these compounds are used in sugarcane crops for the control of invasive plants in Brazil. In the northwest of the country, many species of anurans are distributed in areas common to agriculture. Most of them have reproductive activity restricted to the rainy season, which coincides with the period of greatest environmental contamination. This study aimed to investigate the influence of temperature on the toxicity of the herbicides sulfentrazone, clomazone and diuron in anuran larvae, using specific physiological, biochemical and molecular biomarkers. Our first study investigated the effects of the herbicides sulfentrazone (Boral SC500C®) and clomazone (Gamit®) in tadpoles of Eupemphix nattereri and Rhinella schneideri under different temperatures (28, 32 and 36 ºC), evaluating the antioxidant responses and lipid peroxidation. In our second study, we evaluated the influence of temperature (28 and 34 °C) on the action of diuron and its metabolite 3,4-dichloroaniline (3,4-DCA) on thyroid function and metamorphosis in tadpoles of Lithobates catesbeianus. Our results showed that temperature is an important factor influencing toxicity of the studied herbicides for the different tadpole’s species. Moreover, studied biomarkers were also changed by isolated effects of temperature. Exposure of E. nattereri and R. schneideri to the herbicides clomazone and sulfentrazone altered the antioxidant enzymes activities in tadpoles, in addition to increases in malondialdehyde (MDA) levels, indicating the occurrence of oxidative stress; however, these responses were directly related to the temperatures of exposure for both species. Most of the enzymes had their activities more pronounced at higher temperatures and in combination with the presence of contaminants. These data are probably due to the increased toxicity of contaminants at higher temperatures as a result of increased metabolic rates of cold-blooded tadpoles. Differential activation of the antioxidant system in E. nattereri and R. schneideri suggests that tadpoles of different species may use diverse strategies and adaptive mechanisms to cope with the effects generated by exposure to agrochemicals in habitats where the temperature is a relevant influencing factor. The results of our second study showed that the herbicide diuron and its metabolite 3,4-DCA are potent thyroid deregulators in L. catesbeianus tadpoles, however these endocrine effects are more pronounced at higher temperatures. Besides the induction on expression of TH-related genes, we observed changes in plasma levels of triiodothyronine (T3) and an acceleration in the metamorphosis of tadpoles exposed to the combined effects of high temperature and the presence of contaminants, diuron or 3,4-DCA. Overall, our results suggest that realistic environmental temperatures should be increasingly taken into account in risk studies evaluating the exposure of amphibians to environmental contaminants, such as pesticides. The lack of approach of these variables in laboratory tests can lead to underestimated interpretations of the toxic effects of these and other compounds for different species of amphibians.
Temperature is an important environmental factor influencing the metabolism, development and behavior of cold-blooded animals. However, indirect effects of temperature on natural systems, such as the potential of interaction with environmental contaminants have not been well-characterized for many taxa. Changes in temperature patterns can potentially alter the nature and distribution of many contaminants in the environment, and therefore the current challenge for ecotoxicologists is to predict the risks established by these interactions at biological level. Pesticides are the main group of toxicants present in natural systems and a large part of these compounds are used in sugarcane crops for the control of invasive plants in Brazil. In the northwest of the country, many species of anurans are distributed in areas common to agriculture. Most of them have reproductive activity restricted to the rainy season, which coincides with the period of greatest environmental contamination. This study aimed to investigate the influence of temperature on the toxicity of the herbicides sulfentrazone, clomazone and diuron in anuran larvae, using specific physiological, biochemical and molecular biomarkers. Our first study investigated the effects of the herbicides sulfentrazone (Boral SC500C®) and clomazone (Gamit®) in tadpoles of Eupemphix nattereri and Rhinella schneideri under different temperatures (28, 32 and 36 ºC), evaluating the antioxidant responses and lipid peroxidation. In our second study, we evaluated the influence of temperature (28 and 34 °C) on the action of diuron and its metabolite 3,4-dichloroaniline (3,4-DCA) on thyroid function and metamorphosis in tadpoles of Lithobates catesbeianus. Our results showed that temperature is an important factor influencing toxicity of the studied herbicides for the different tadpole’s species. Moreover, studied biomarkers were also changed by isolated effects of temperature. Exposure of E. nattereri and R. schneideri to the herbicides clomazone and sulfentrazone altered the antioxidant enzymes activities in tadpoles, in addition to increases in malondialdehyde (MDA) levels, indicating the occurrence of oxidative stress; however, these responses were directly related to the temperatures of exposure for both species. Most of the enzymes had their activities more pronounced at higher temperatures and in combination with the presence of contaminants. These data are probably due to the increased toxicity of contaminants at higher temperatures as a result of increased metabolic rates of cold-blooded tadpoles. Differential activation of the antioxidant system in E. nattereri and R. schneideri suggests that tadpoles of different species may use diverse strategies and adaptive mechanisms to cope with the effects generated by exposure to agrochemicals in habitats where the temperature is a relevant influencing factor. The results of our second study showed that the herbicide diuron and its metabolite 3,4-DCA are potent thyroid deregulators in L. catesbeianus tadpoles, however these endocrine effects are more pronounced at higher temperatures. Besides the induction on expression of TH-related genes, we observed changes in plasma levels of triiodothyronine (T3) and an acceleration in the metamorphosis of tadpoles exposed to the combined effects of high temperature and the presence of contaminants, diuron or 3,4-DCA. Overall, our results suggest that realistic environmental temperatures should be increasingly taken into account in risk studies evaluating the exposure of amphibians to environmental contaminants, such as pesticides. The lack of approach of these variables in laboratory tests can lead to underestimated interpretations of the toxic effects of these and other compounds for different species of amphibians.
Descrição
Palavras-chave
Anfíbios, Temperatura, Agrotóxicos, Clomazone, Sulfentrazone, Diuron, Estresse oxidativo, Desreguladores endócrinos