Disrupting effects of diuron and metabolite 3,4-DCA (3,4 - dichloroaniline) on tadpoles of Lithobates catesbeianus (Anura: Ranidae) exposed to thermal stress

Abstract

The increase in temperature and other environmental effects influenced by global climate changes (GCC) have documented several impacts on global amphibian populations. Changes in environmental variables can potentially alter the chemical toxicokinetics and therefore, a current challenge is to predict the risks established by the interactions between nonchemical and chemical stressors at biological level. In Brazil, many species of amphibians are distributed in common agriculture areas and they mainly breed during the rainy season, which is the period of greatest environmental pesticides contamination. Diuron is a common herbicide used on crops of sugar cane and citrus in the southeastern Brazil with a long residual effect and high potential for contamination. In the environment, diuron generates a persistent metabolite, 3,4-DCA (3,4-dichloroaniline), commonly found in soil and water from agricultural areas. Some studies have pointed endocrine disrupting effects of diuron in many organisms, including aquatic vertebrates. In frogs, the exposures to endocrine-disrupting chemicals are of special concern because these substances can disrupt the normal thyroid activity, which regulates the metamorphosis process. During the initial stages of life, the exposure to thyroid disruptors may impair the adaptability of the tadpoles to adequately respond to variables influenced by GCC, such as temperature increase. This study aims to investigate the effects caused by interaction between temperature and the known endocrine disruptor diuron and its metabolite 3,4-DCA in tadpoles of Lithobates catesbeianus, the American bullfrog, using endpoints for evaluating endocrine alterations linked to thyroid activity. For this, morphological examinations will be performed on thyroid gland and gene expressions of dio2, dio3, tr-alpha and tr-beta will be investigated and related to circulating thyroid hormones. Effects in the growth, development and the occurrence of abnormalities will also be recorded after exposure to different treatments. (AU)