Using sets of behavioral biomarkers to assess short-term effects of pesticide: a study case with endosulfan on frog tadpoles

Abstract

Pesticides and other chemicals often have detrimental effects at environmental concentrations. Many amphibian species are particularly threatened because of their susceptibility but also because wetlands are often polluted. Behavioral assessments of toxicity have the advantage of showing sublethal effects but quantitative measures at varied scales of integrations are rarely considered together. In this study, we aimed at showing that these behavioral endpoints could be differently affected across time and concentrations, and be biomarkers of toxicity. To this end, we tested the effects of an organochlorine pesticide (endosulfan) on amphibians during a standard 96 h test. We evaluated possible lag effects in continuing the analyses after removal of the pesticide. The study was based on 240 tadpoles (4 pesticide treatments: 0.4, 3, 22, and 282 μg/l, 1 control and 1 solvent-control). Abnormal behaviors such as lying and swirling rapidly were exhibited only in the presence of the pesticide. Essential functions such as breathing and feeding were deeply affected by the pesticide: contaminated tadpoles breathed and fed less than control tadpoles. They also moved less and occupied a more central position in the aquariums in the presence of the pesticide. A higher mortality was only found at the highest concentration. These results suggest that endosulfan is toxic to amphibians at environmental concentrations. Behavioral markers showed potential as early warning systems. They should thus be used in complement to other markers to detect sublethal effects only a few days after application of the pesticide and at concentrations where mortality does not occur.

Effects of low dose endosulfan exposure on brain neurotransmitter levels in the African clawed frog Xenopus laevis

“…This increase of serotonin enhances satiety and inhibits feeding. Our results on food acquisition are in agreement with previous studies on amphibian tadpoles which showed that feeding rates were decreased or even suppressed after endosulfan exposure (Broomhall and Shine, 2003;Denoël et al, 2012). This is also consistent with the high observed level of serotonin and suggests that the decrease of feeding activity may be linked to the increase of serotonin concentration in the brain.…”

“…This may be due to the fact that Sillar et al (1998) used high doses, at least 400-fold higher than the ones used in the present paper. Previous studies showed also that convulsions, which can result from uncorrected neural discharges, were not produced at low environmental endosulfan concentrations (Brunelli et al, 2009;Denoël et al, 2012). Finally, exposure to SSRI (Selective Serotonin Reuptake Inhibitor) causes a growth reduction of 35% in X. laevis (Conners et al, 2009) but no effects of endosulfan were found on growth rates in the present study whereas previous research highlighted the presence or absence of effects.…”

“…For this reason, there is a need to develop monitoring methods to assess the risks induced by such pollutants. Detrimental effects of endosulfan such as reduced survival (Rohr et al, 2003;Jones et al, 2009;Shenoy et al, 2009), growth inhibition (Dimitrie, 2010), disturbed behavioural patterns (Denoël et al, 2012(Denoël et al, , 2013a, body deformities (Lavorato et al, 2013), or metamorphosis timing perturbations (Lavorato et al, 2013) have been already reported on amphibians. Nervous system is the main target of endosulfan (EPA, 2002) but, to the best of our knowledge, no study investigated the impacts of endosulfan on the nervous system of amphibians.…”

Sensitivity of Boana pulchella (Anura: Hylidae) Tadpoles to Environmentally Relevant Concentrations of Chlorpyrifos: Effects at the Individual and Biochemical Levels

“…The use and application of biomarkers in ecotoxicology have extensively been discussed since their proposal as useful predictors of ecologically relevant effects (Shugart et al 1992; Forbes et al 2006). In recent years, the classical concept has been extended to include higher biological levels (Handy et al 2003; Denoël et al 2012). In herpetological ecotoxicology, lethal and sublethal endpoints like mortality and morphological and behavioral alterations during embryonic and larval development were the first and most amply described biomarkers of exposure (Venturino et al 2003).…”

Developmental toxicity and risk assessment of nonylphenol to the South American toad, Rhinella arenarum

“…As a measure of developmental hazard, the teratogenic potential (TP) (Aronzon et al, 2011a) was estimated as the ratio between the NOEC value for lethality and sublethal effects and it was compared with the maximal value of 1.5 (ASTM, 1993) which implies large separation of the mortality and malformations concentration ranges and, therefore, a great potential for all embryos to be malformed in absence of significant embryo mortality. Behavioral alterations such as abnormal fast rotations which are a sign of neurotoxic stress; lying on the lateral or dorsal side, abnormal breathing, feeding and swimming patterns were evaluated (Denoël et al, 2012). Smooth movements of the Petri-dishes, followed by stimulation with a light source were done.…”