Interactive effects of pesticide mixtures, predators, and environmental regimes on the toxicity of two pesticides to red‐eyed tree frog larvae

Abstract

Global amphibian declines have many corroborative causes, and the use of pesticides in agriculture is a likely contributor. In places with high pesticide usage, such as Costa Rica, agrochemical pesticides may interact with other factors to contribute to rapid species losses. Classical ecotoxicological studies rarely address the effects of a pesticide in combination with other stressors. The present study investigated the synergistic roles of 2 pesticides (chlorothalonil and endosulfan), predator stress, and environmental regimes (controlled laboratory environments versus ambient conditions) on the survival of red-eyed tree frog larvae (Agalychnis callidryas). No synergistic effects of pesticide mixtures or predator stress were found on the toxicity of either chlorothalonil or endosulfan. Both pesticides, however, were considerably more toxic under realistic ambient temperature regimes than in a climate-controlled laboratory. Overall, endosulfan displayed the highest toxicity to tadpoles, although chlorothalonil was also highly toxic. The median lethal concentration estimated to kill 50% of a tested population (LC50) for endosulfan treatments under ambient temperatures was less than one-half of that for laboratory treatments (3.26 µg/L and 8.39 µg/L, respectively). Studies commonly performed in stable temperature-controlled laboratories may significantly underestimate toxicity compared with more realistic environmental regimes. Furthermore, global climatic changes are leading to warmer and more variable climates and may increase impacts of pesticides on amphibians.

Choice of experimental venue matters in ecotoxicology studies: Comparison of a laboratory-based and an outdoor mesocosm experiment

“…Previous comparisons of ecotoxicological effects of contaminants between different types of venues have obtained conflicting conclusions (Bernal et al, 2009a,b;Edge et al, 2013;Johnson et al, 2013;Saura-Mas et al, 2002). Laboratory-based tests have the advantage that experimental conditions are relatively easy to standardize, high sample sizes can be achieved, and experimental treatments can be varied with high precision.…”

“…One way of testing if laboratorybased experiments deliver ecologically meaningful results is to compare pesticide effects across different experimental venues (Skelly, 2002). Surprisingly, only a handful of such studies have been conducted, and most of these have only focussed on survival (Bernal et al, 2009a,b;Johnson et al, 2013; but also see Edge et al, 2013;Lanctôt et al, 2014;Saura-Mas et al, 2002).…”

Bioaccumulation kinetics of the conventional energetics TNT and RDX relative to insensitive munitions constituents DNAN and NTO in Rana pipiens tadpoles

“…Aquatic toxicology studies using larval amphibians are limited to evaluations of the lethal effects of TNT to Xenopus laevis and to Rana catesbeiana . Given the broad public concern over reported declines in global amphibian populations and the suspected contribution of chemical contamination to the complex interaction of stressors contributing to those declines , investigations of the potential for ecototoxicological effects of explosives on the sensitive larval life stages of amphibians were pursued. The present study investigated the Northern leopard frog, Rana pipiens , an important ecological indicator within North America and a closely‐related phylogenetic relative of Rana capito , a candidate for endangered species listing and inhabitant of military installations across the southeastern United States .…”

Time-dependence in mixture toxicity prediction

“…Such research has included in vitro and in vivo studies (Boyd et al, 2013; Cedergreen et al, 2012; Coors et al, 2012), toxicity assessment using combined effects models (Crépet et al, 2013; Hertzberg et al, 2013; Moser et al, 2012; Rider et al, 2008; Webster, 2013), evaluating stressor impacts environmentally (Allan et al, 2012; Florian et al., 2013; Løkke 2010), risk assessment studies (Johnson et al, 2013; Løkke et al, 2013; Meek, 2013; Moore and Teed, 2013) and examining chemical reactivity within complex mixtures (Goel et al, 2013). Although the specifics of such research vary, the common goal is improving the ability to predict the effects of exposure to chemical mixtures.…”