Effects of sublethal concentrations of atrazine and nitrate on metamorphosis of the African clawed frog

Abstract

Tadpoles of the African clawed frog (Xenopus laevis) were exposed to sublethal concentrations of atrazine (0, 40, and 320 microg/L) and nitrate (0, 37, and 292 mg/L) from feeding stage to metamorphosis. A 3 x 3 factorial design was used to identify both single and interactive effects. At metamorphosis, tadpole weight, snout-vent length (SVL), and hematocrit were determined. Mean mortality was greater in tanks receiving 320 microg/L atrazine; nitrate had no effect on mortality. Significant differences for all mean traits at metamorphosis occurred among atrazine treatments; higher atrazine exposure increased time to metamorphosis and decreased weight, SVL, and hematocrit. Nitrate treatments were not significantly different. Significant interaction tests between atrazine and nitrate occurred for weight and SVL at metamorphosis; the specific type of interaction varied among treatments. Assuming an additive mixture model, at low atrazine (40 microg/L), the addition of 37 mg/L nitrate produced SVL values less than expected (a synergistic effect) while the addition of 292 mg/L nitrate yielded SVL values greater than expected (an antagonistic effect). A similar response was noted for tadpoles in the 320-microg/L atrazine treatments. These results indicate that environmentally realistic concentrations of atrazine exert a negative impact on amphibian metamorphosis. Also, this study suggests that mixtures of agricultural chemicals, even if sublethal, may exert negative and not necessarily consistent mixture effects.

Intraspecific Differences in Responses of Marsh Frog (Pelophylax ridibundus) Tadpoles Exposed to Environmentally Relevant and Acute Levels of Ammonium Nitrate Fertilizer

“…Johansson et al (2001), Sullivan and Spence (2003), Edwards et al (2006), andGrifis-Kyle (2007) similarly reported that the duration of metamorphosis increased considerably in the presence of nitrogen. However, in studies canied out with various amphibian species (Pseudaris triseriata [Hecnar 19951, Bufo bufo [Xu and Oldham 19971, and Triturus ' "1 * D Pond Concentration ( m a ) Figure 6.…”

Interactions between estrogenic chemicals in binary mixtures investigated using vitellogenin induction and factorial analysis

“…Similar experimental designs have been applied successfully to testing the in vivo interactions between individual chemicals not only in fish (Lin and Janz, 2006), but also in amphibians (Sullivan and Spence, 2003). This statistical experimental approach does not require dose-effect equations for each individual chemical of the mixture per se (Feron and Groten, 2002), and can avoid most of the limitations of the CA model.…”

“…In the last two decades, increased attention has been paid to synthetic and natural chemicals that have the potential to interfere with the endocrine systems of organisms (Matthiessen, 2003;Sullivan and Spence, 2003). Extensive evidence now exists to show that these substances, termed endocrine disrupting chemicals (EDCs), may be responsible for adverse reproductive and developmental effects in both wildlife and humans (OECD, 1997;US EPA, 2002).…”

The cause of global amphibian declines: a developmental endocrinologist's perspective

“…Perchlorate, a contaminant associated with rocket fuel production, is a well-known example (Goleman et al, 2002a;Goleman et al, 2002b;Ortiz-Santaliestra and Sparling, 2007;Theodorakis et al, 2006). A number of pesticides can inhibit or delay anuran metamorphosis as well (Distel and Boone, 2009;Howe et al, 2004;Mackey and Boone, 2009;Sparling and Fellers, 2009), including atrazine (Carr et al, 2003;Sullivan and Spence, 2003). Some pesticides accelerate metamorphosis -for example, atrazine accelerated metamorphosis in at least two species of salamanders (Forson and Storfer, 2006b;Rohr et al, 2004) -and some can even have biphasic effects (Brodeur et al, 1997).…”