Químicos Pertubadores Endócrinos / EDCs
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New effects of Roundup on amphibians: Predators reduce herbicide mortality; herbicides induce antipredator morphology
RICK A. RELYEA1
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA
Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA
The use of pesticides is important for growing crops and protecting human health by reducing the prevalence of targeted pest species. However, less attention is given to the potential unintended effects on nontarget species, including taxonomic groups that are of current conservation concern. One issue raised in recent years is the potential for pesticides to become more lethal in the presence of predatory cues, a phenomenon observed thus far only in the laboratory. A second issue is whether pesticides can induce unintended trait changes in nontarget species, particularly trait changes that might mimic adaptive responses to natural environmental stressors. Using outdoor mesocosms, I created simple wetland communities containing leaf litter, algae, zooplankton, and three species of tadpoles (wood frogs [Rana sylvatica or Lithobates sylvaticus], leopard frogs [R. pipiens or L. pipiens], and American toads [Bufo americanus or Anaxyrus americanus]). I exposed the communities to a factorial combination of environmentally relevant herbicide concentrations (0, 1, 2, or 3 mg acid equivalents [a.e.]/L of Roundup Original MAX) crossed with three predator-cue treatments (no predators, adult newts [Notophthalmus viridescens], or larval dragonflies [Anax junius]). Without predator cues, mortality rates from Roundup were consistent with past studies. Combined with cues from the most risky predator (i.e., dragonflies), Roundup became less lethal (in direct contrast to past laboratory studies). This reduction in mortality was likely caused by the herbicide stratifying in the water column and predator cues scaring the tadpoles down to the benthos where herbicide concentrations were lower. Even more striking was the discovery that Roundup induced morphological changes in the tadpoles. In wood frog and leopard frog tadpoles, Roundup induced relatively deeper tails in the same direction and of the same magnitude as the adaptive changes induced by dragonfly cues. To my knowledge, this is the first study to show that a pesticide can induce morphological changes in a vertebrate. Moreover, the data suggest that the herbicide might be activating the tadpoles’ developmental pathways used for antipredator responses. Collectively, these discoveries suggest that the world’s most widely applied herbicide may have much further-reaching effects on nontarget species than previous considered.
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Endocrine disruption in crustaceans due to pollutants:
A review
Enrique M. Rodríguez a,!, Daniel A. Medesani a, Milton Fingerman b
a Department of Biodiversity and Experimental Biology, FCEyN, University of Buenos Aires, Argentina
b Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana 70118, USA
Received 12 December 2005; received in revised form 28 April 2006; accepted 29 April 2006
Available online 4 May 2006
a Department of Biodiversity and Experimental Biology, FCEyN, University of Buenos Aires, Argentina
b Department of Ecology and Evolutionary Biology, Tulane University, New Orleans, Louisiana 70118, USA
Received 12 December 2005; received in revised form 28 April 2006; accepted 29 April 2006
Available online 4 May 2006
The main endocrine-regulated processes of crustaceans have been reviewed in relation to the effects of endocrine-disrupting compounds (EDCs). Molting has been shown to be inhibited by several organic pollutants, such as xenoestrogens and related compounds, as well as by some pesticides.Most of these disrupters are thought to interfere with ecdysone at target tissues, although only for a few has this action been demonstrated in vitro. The heavy metal cadmium appears to inhibit some ecdysone secretion. Juvenoid compounds have also been shown to inhibitmolting, likely by interfering with the stimulatory effect of methyl farnesoate. A molt-promoting effect of emamectin benzoate, a pesticide, has also been reported. As for reproduction, a variety of organic compounds, including xenoestrogens, juvenoids and ecdysteroids, has produced abnormal development of male and female secondary sexual characters, as well as alteration of the sex ratio. Cadmium and copper have been shown to interfere with hormones that stimulate reproduction, such as methyl farnesoate, as well as with secretion of the gonad inhibiting hormone, therefore affecting, for example, ovarian growth. Several heavy metals were able to produce hyperglycemia in crustaceans during short times of exposure; while a hypoglycemic response was noted after longer exposures, due to inhibition of secretion of the crustacean hyperglycemic hormone. The ecological relevance of EDCs on crustaceans is discussed, mainly in relation to the identification of useful biomarkers and sentinel species. New experimental approaches are also proposed.
© 2006 Elsevier Inc. All rights reserved.
Fuente:http://www.sciencedirect.com/
© 2006 Elsevier Inc. All rights reserved.
Fuente:http://www.sciencedirect.com/
GLYPHOSATE—THE CONSERVATIONIST’S FRIEND?
P. CHRISTOFFOLOTI/UNIVERSITY OF SÃO PAULO; I. HEAP/WEEDSMART LLC
Weeds resistant to the powerhouse herbicide glyphosate not only threaten the livelihoods of farmers worldwide, but they could have environmental downsides as well. Among the worst, glyphosate’s disappearance could increase the loss of topsoil, require farmers to switch to more harmful herbicides, and force them to use more fuel to rid their fields of weeds.
The current combination of herbicide-resistant crops and herbicide use is hardly an environmental panacea. A 2003 farm-scale evaluation in the United Kingdom, for example, found that the combination contributed to a loss of biodiversity both by reducing the numbers of weeds and by indirectly affecting insects that rely on those weeds for food. Many governments have also been cautious about allowing the use of herbicideresistant crops for fear that genes that confer herbicide resistance could spread far beyond agricultural fields. Despite such concerns, many agricultural researchers now say glyphosate-resistant (GR) crops have had widespread environmental benefits, at least compared with the previously used alternatives. “Glyphosate-resistant crop weed management systems are generally safer to the environment than what they replace, and in many cases much safer,” says Stephen Duke, a plant physiologist at the U.S. Department of Agriculture’s Agricultural Research Service in Oxford, Mississippi. One of the biggest benefits of GR crops is their indirect impact on topsoil. Modern farming encourages heavy topsoil losses because farmers traditionally plow fields before planting seeds. Turning over the topsoil buries many weed seeds that were present under 4 to 6 inches of dirt. Although that reduces the likelihood that weeds will compete with emerging crop plants, it also dramatically increases the amount of topsoil that washes away with rain and irrigation. By contrast, many farmers don’t plow their fields before planting GR crops. Instead, they simply plant seeds and spray glyphosate on their fields shortly after their crops have emerged, wiping out their weedy competitors. The upshot is that herbicide-resistant crops often require minimal
The current combination of herbicide-resistant crops and herbicide use is hardly an environmental panacea. A 2003 farm-scale evaluation in the United Kingdom, for example, found that the combination contributed to a loss of biodiversity both by reducing the numbers of weeds and by indirectly affecting insects that rely on those weeds for food. Many governments have also been cautious about allowing the use of herbicideresistant crops for fear that genes that confer herbicide resistance could spread far beyond agricultural fields. Despite such concerns, many agricultural researchers now say glyphosate-resistant (GR) crops have had widespread environmental benefits, at least compared with the previously used alternatives. “Glyphosate-resistant crop weed management systems are generally safer to the environment than what they replace, and in many cases much safer,” says Stephen Duke, a plant physiologist at the U.S. Department of Agriculture’s Agricultural Research Service in Oxford, Mississippi. One of the biggest benefits of GR crops is their indirect impact on topsoil. Modern farming encourages heavy topsoil losses because farmers traditionally plow fields before planting seeds. Turning over the topsoil buries many weed seeds that were present under 4 to 6 inches of dirt. Although that reduces the likelihood that weeds will compete with emerging crop plants, it also dramatically increases the amount of topsoil that washes away with rain and irrigation. By contrast, many farmers don’t plow their fields before planting GR crops. Instead, they simply plant seeds and spray glyphosate on their fields shortly after their crops have emerged, wiping out their weedy competitors. The upshot is that herbicide-resistant crops often require minimal
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