Toxicity of endosulfan on embryo‐larval development of the South American toad Rhinella arenarum

Abstract

Endosulfan is a widely used pesticide despite its extreme toxicity to a variety of taxa and its worldwide ban. The aim of the present study was to evaluate the acute and chronic toxicity of endosulfan on the embryonic-larval development of the common South American toad Rhinella arenarum. The results showed that lethal and sublethal effects increased with concentration and exposure time. The sensitivity to endosulfan increased during the larval period, the complete operculum stage (S.25) being the most sensitive (504-h median lethal concentration [LC50] = 0.01 mg endosulfan/L; 10% lethal concentration [LC10] = 0.004 mg endosulfan/L). Endosulfan exposure caused morphological abnormalities such as general underdevelopment, edema, gill malformations, and cellular dissociation as well as neurotoxicity. Our results also showed that larvae exposed to concentrations of 0.005 mg endosulfan/L and 0.01 mg endosulfan/L completed metamorphosis earlier than controls, but with underdevelopment. The 240-h teratogenic index was 6.13, implying a high risk for embryos to be malformed in the absence of significant embryonic lethality. Because the hazard quotients for chronic exposure were over 1, the level of concern value and toxicity endpoints obtained in the present study for R. arenarum occurred at concentrations lower than the levels of endosulfan reported in the environment, this pesticide should be considered a potential risk for this species.

Differential Uptake of Endosulfan in the South American Toad Under Sublethal Exposure

“…In a recent publication (Svartz et al 2014), we reported the high toxicity of endosulfan to R. arenarum embryos and larvae with 504-h LC50 values of 0.03 (range 0.014-0.05) and 0.01 (range 0.006-0.015) mg L -1 , respectively. Moreover, we had characterized both lethal and sublethal effects of endosulfan on the embryo-larval development of R. arenarum, whereas in the present study we attempt to elucidate any correlation between developmental stage sensitivity and uptake of the pesticide.…”

“…For each experimental condition, 60 embryos or larvae were placed in triplicate (by each time period) in 20 cm-diameter glass Petri dishes containing 200 mL of test solution, which were entirely replaced every 48 h. Temperature between 20 ± 2°C and a 12:12-h light-to-dark photoperiod were maintained throughout the experiments, which lasted 504 h. Test solutions ranged between 0.001 and 0.005 and between 0.0005 and 0.075 mg of endosulfan L -1 for embryos and larvae, respectively. This concentration range was selected considering that the maximum exposure concentration was lower than the LC10 values obtained in our previous study (Svartz et al 2014). Tadpoles were fed with balanced fish food TetraColor (Tetra): Eighteen granules were placed in each Petri dish every 48 h. The uptake and wet weight were measured at three exposure times: 96, 240, and 504 h. At each time, 50 organisms were removed from each replicate, thoroughly washed with 200 mL of AS, blotted dry on absorbent paper, and then weighed and stored at -20°C for analytical assessment.…”

“…Bionda et al (2013) reported that amphibians in altered Argentinean agroecosystems had lower egg and larval survival compared with organisms from noncultivated area with population projections less favorable leading to extinction in crop-dominated areas. Several laboratory studies reported adverse effects of endosulfan on amphibian embryo-larval development, i.e., lethality in various species at environmentally relevant concentrations (Jones et al 2009;De Jong Westman et al 2010), delay to complete metamorphosis (Brunelli et al 2009), malformations of gills (Bernabó et al 2008), failures in the endocrine system (Goulet and Hontela 2003), and neurotoxic effects (Agostini et al 2009;Denoël et al 2013;Svartz et al 2014). However, most toxicity studies evaluate adverse effects under acute exposure condition only during certain periods of the life cycle.…”

“…In this context, the aim of this study was to evaluate, in a comparative way, endosulfan uptake in the embryonic and larval development of R. arenarum. In addition, we also sought to assess a correlation with the differential sensitivity we previously reported (Svartz et al 2014) and the uptake of the pesticide under several periods of exposures of increasing time by means of the AMPHITOX test.…”

“…AMPHITOX is a set of toxicity tests that employs embryos and larvae of R. arenarum providing information on mortality, malformations, delayed development, decreased growth, and behavioral abnormalities (Herkovits et al 2002;Herkovits and Pérez-Coll 2003;Hutler Wolkowicz et al 2013;Svartz et al 2012). Moreover, AMPHITOX allows evaluation of the uptake of a chemical (Pérez-Coll et al 1999;Herkovits and Pérez-Coll 2007;Pérez-Coll et al 2008;Aronzon et al 2014) as the assessment of stage-dependent susceptibility (Pérez-Coll and Herkovits 1990;Herkovits and Pérez-Coll 1993;Brodeur et al 2009;Svartz et al 2014) and expands the evaluation time, which allows obtaining acute, short-term chronic, and chronic toxicity results. In this context, the aim of this study was to evaluate, in a comparative way, endosulfan uptake in the embryonic and larval development of R. arenarum.…”