Response of the amphibian tadpole (Xenopus laevis) to atrazine during sexual differentiation of the testis

Abstract

Xenopus laevis tadpoles were exposed for 48 h during sexual differentiation to atrazine at 21 microg/L under static laboratory conditions at 21+/-0.5 degrees C. After this exposure period, tadpoles were fixed and the kidney-gonad complex was microdissected. Quantitative histological analysis of the gonad revealed a 57% reduction in testicular volume among atrazine-exposed tadpoles. In addition, primary spermatogonial cell nests that represent germ cells for the life of the organism were reduced by 70%. Nursing cells, which provide nutritive support for the developing germ cells, had declined by 74%. Testicular resorption was observed among 70% and aplasia or failure of full development of the testis was recorded in 10% of the atrazine-exposed tadpoles. Because cell nests represent the pool of primordial germ cells for the reproductive life of the organism, the combined reduction in spermatogonial cell nests and nursing cells suggest that a pulse exposure to 21 microg/L of atrazine during sexual differentiation could significantly reduce reproduction during the reproductive life of these animals.

Atrazine-Induced Aromatase Expression Is SF-1 Dependent: Implications for Endocrine Disruption in Wildlife and Reproductive Cancers in Humans

“…In fact, the activity of atrazine and simazine at 10 −7 M (21.57 mol/L) in the present study is in the range that chemically castrates and feminizes male amphibians (0.1–20 ppb; 1 ppb = 1 mol/L) (Carr et al 2003; Hayes 2004, 2005; Hayes et al 2002a, 2002b, 2003, 2006a, 2006b; McKoy et al 2002; Miyahara et al, unpublished data; Reeder et al 1998; Tavera-Mendoza et al 2002) and fish (6 ppb) (Moore and Waring 1998). Thus, the present study is also significant because the effects in wildlife likely occur through the same molecular mechanisms as documented here; however, the cell lines and molecular tools are not available for wildlife species to examine these effects on this same level.…”

Exposure, Postexposure, and Density-Mediated Effects of Atrazine on Amphibians: Breaking Down Net Effects into Their Parts

“…Nevertheless, the possibility of cross-generational compensation suggests that combining experiments that span life stages with demographic models might be particularly insightful for evaluating the population-level effects of environmental stress. Despite the aforementioned admonishments, this study, and evidence that exposure of amphibians to low levels of atrazine can increase mortality (Storrs and Kiesecker 2004), impair reproductive development (Hayes et al 2002a, 2002b, 2003; Tavera-Mendoza et al 2002a, 2002b), and adversely interact with natural stressors (Boone and James 2003; Kiesecker 2002; Rohr and Palmer 2005), must raise concerns about the role of this widespread, persistent, and mobile herbicide in the international decline of amphibians. Certainly, more research on the effects of atrazine on amphibians is necessary.…”

“…The endocrine-disrupting properties of atrazine have been implicated in exposures between 25 and 0.1 ppb inducing gonadal abnormalities and hermaphroditism in leopard frogs ( Rana pipiens ) and African clawed frogs ( Xenopus laevis ) (Carr et al 2003; Hayes et al 2002a, 2002b, 2003; Tavera-Mendoza et al 2002a, 2002b). Exposure to 3 ppb has increased tadpole mortality (Storrs and Kiesecker 2004) and susceptibility to infection (Kiesecker 2002).…”

Pesticide Mixtures, Endocrine Disruption, and Amphibian Declines: Are We Underestimating the Impact?

“…Only a few studies have examined the effects of pesticide mixtures on amphibians (Christin et al 2003; Dawson and Wilke 1991; Gendron et al 2003; Howe et al 1998; Mazanti 1999; Mazanti et al 2003; Relyea 2004), but chemicals were examined at much higher concentrations than those examined here, only toxicity was examined, and the chemical mixture in the present analysis was not examined. Further, fewer than 20 published laboratory studies (Boegi et al 2002; Hayes 1997a, 1998, 2000, 2004, 2005; Hayes et al 1997, 2002a, 2002b, 2002c; Lutz and Kloas 1999; Noriega and Hayes 2000; Palmer and Palmer 1995; Palmer et al 1998; Tavera-Mendoza et al 2002a, 2002b) and four field studies (du Preez et al 2005; Hayes et al 2002b, 2002c; Reeder et al 1998) have addressed low-concentration, endocrine-disrupting effects of pesticides (single compounds only) on amphibians. A few studies have examined amphibians in the wild (Harris et al 1998a, 1998b; Ouellet et al 1997; Sparling et al 2001), although establishing cause and effect in such studies is difficult.…”