Influência dos herbicidas roundup® original di e boral® 500 SC, isolados e em misturas, sobre biomarcadores metabólicos, do balanço oxidativo e da metamorfose de melanophryniscus admirabilis (Anura : Bufonidae)

Abstract

Melanophryniscus admirabilis is a bufonid species endemic to the Southern Atlantic Forest (RS, Brazil), a region with agricultural activities which can impact this species. The objectives of this work were to evaluate alterations in metabolic parameters (glycogen, proteins and uric acid levels), oxidative balance (lipid peroxidation and activity of enzymes superoxide dismutase, catalase and glutathione S-transferase), morphological parameters (mass, length and body index) and metamorphosis (timing to stages 42, 46 and time interval between these stages) of M. admirabilis tadpoles exposed to the herbicides Roundup® Original DI (a.i. glyphosate; R1: 2,5 mg.L-1; R2: 5,0 mg.L-1) and Boral® 500 SC (a.i. sulfentrazone; B1: 1,0 mg.L-1; B2: 2,0 mg.L-1), and to herbicides mixtures (Mixture 1: R1+B1; Mixture 2: R2+B1; Mixture 3: R1+B2; Mixture 4: R2+B2). Egg masses were collected, transported and reared, in laboratory (23±1°C; 12h:12h) until eclosion in tadpoles (Experiment 1: 82; Experiment 2: 123), which were acclimated (5 days) and then, exposed (96h) to the herbicides (except Control group). After exposure, tadpoles were weighed, measured and euthanized (liquid nitrogen) (Experiment 1) or relocated in aquariums with dechlorinated tap water and rocky sediment until metamorphosis (Experiment 2), and then, weighed, measured and euthanized. In Chapter 1, for tadpoles, there was maintenance of morphological parameters, higher levels of glycogen and uric acid, and reduction in protein levels, indicating mobilization of energetic and structural metabolites, and the possible role of uric acid as antioxidant. Reduced lipid peroxidation and enzymatic activities suggests mobilization of constitutive mechanisms of this species. Nevertheless, these results can reduce fitness and success of these animals. In Chapter 2, the herbicide exposure resulted in mortality and, in metamorphosed tadpoles, reduced lipid peroxidation, mostly in mixture groups, suggesting mobilization of constitutive mechanisms of these animals. The enzymatic suppression can jeopardize herbicide metabolization, impacting animals’ survival. In Chapter 3, for metamorphosed tadpoles, aside from mortality, the animals maintained mass, growth and body index, indicating energetic allocation to body maintenance, impacting biotransformation. Timing to metamorphosis, for stage 42, were longer (R2, 4%) or reduced (Mixtures 2 - 13%, 3 and 4 - 6%); reduced for stage 46 (Mixtures 2 -15% and 4 - 12%) and, for time interval, reduced (R2, 59%) or absence of effect. These results suggest Roundup as endocrine disruptor, with synergic action with Boral (mixture groups), shortening metamorphosis, which can threaten this species development and, possibly, lead to death. These results demonstrate the risks imposed to M. admirabilis by pesticide exposure, compromising fitness, survival and success of metamorphic and post-metamorphic life cycle stages. Therefore, elucidation of the effects of pesticides, especially in mixtures, control and monitoring of these pollutants in this region are extremely relevant for conservation of this endemic species.