Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

Pesticide combinations imperil frogs

06.02.2006



Tadpoles raised in water polluted with a combination of nine pesticides, fungicides and herbicides typical of ponds around Midwestern cornfields take longer to become frogs and end up smaller, making it harder for them to eat their normal prey and making them easier prey for other animals. The top frog is having trouble eating a cricket, while the snake has no trouble swallowing the smaller frog.



The pesticide brew in many ponds bordering Midwestern cornfields is not only affecting the sexual development of frogs, but is making them more prone to deadly bacterial meningitis, according to a new study by University of California, Berkeley, scientists.

These physiological effects combine with environmental disruptions to make the life of a frog seem like something out of a horror movie and are likely among the factors causing a decline in amphibian populations worldwide, the researchers said.

Tadpoles raised in water polluted with a combination of nine pesticides, fungicides and herbicides typical of ponds around Midwestern cornfields take longer to become frogs and end up smaller, making it harder for them to eat their normal prey and making them easier prey for other animals. The top frog is having trouble eating a cricket, while the snake has no trouble swallowing the smaller frog.



"If you look at one of these frogs, it’s probably a hermaphrodite - plus, it metamorphoses late, which means it is subject to its pool drying up before it can become a frog," said lead researcher Tyrone Hayes, professor of integrative biology at UC Berkeley. "It’s also smaller, if it metamorphoses at all, which increases the likelihood it will be eaten and decreases its ability to eat. Plus, it’s immuno-suppressed, so more prone to die from infection."

The stress on the frogs is increasing stress hormone levels, he found, which in turn create holes in the thymus gland that likely cause the impaired immune response.

"It’s not the pesticides alone or introduced predators or ultraviolet light or global warming that’s causing this decline, but the interaction between these on an animal that is pretty sensitive to its environment," said Hayes.

In the new paper, published online last week in the journal Environmental Health Perspectives, Hayes and his colleagues report four years of experiments showing that, while some of the pesticides, herbicides and fungicides used on corn fields may not by themselves have a noticeable impact on frogs, in combination they create significant effects. Among these are delayed maturation - the tadpoles take longer to metamorphose into frogs - retarded growth and an increased susceptibility to meningitis caused by normally benign bacteria.

Four years ago, Hayes showed that atrazine, the most common weed killer used on corn in the United States, disrupts the sexual development of frogs, feminizing males into hermaphrodites - frogs with female sex organs invading their testes - decreasing the size of their vocal organs, which are critical to mating success, and causing a tenfold drop in testosterone in mature male frogs.

In the current study, he looked again at atrazine as well as three other herbicides, two fungicides and three insecticides used on Midwestern cornfields - a subset of more than two dozen pesticides approved for use. All nine were found in the scientists’ study area in Nebraska in pools of water beside cornfields early in the growing season, when spraying typically occurs. Levels ranged from 0.1 parts per billion (ppb) to 10 or more ppb.

Native northern leopard frogs (Rana pipiens) raised in water with only one of these nine pesticides at 0.1 ppb appeared normal, though the fungicide propiconazole caused a small but significant increase in the time it took tadpoles to start metamorphasis. The insecticide tebupirimphos caused a small but statistically significant decrease in the size and weight of mature frogs.

Mixtures, however, had a much stronger effect. All nine compounds together at 0.1 ppb - one of the lower concentrations measured in the field - lengthened the time to metamorphosis by 15 days, or about 25 to 30 percent. The mixture also caused a frog mortality of 35 percent.

All nine compounds together also produced a startling effect: The longer a tadpole took to mature into a frog, the smaller it was. It’s normally the other way around, Hayes said. Separately, six of the pesticides did not affect this correlation, but three disrupted it so that there was no relationship between time to metamorphosis and size at metamorphosis.

"In humans, this is like saying, ’The longer you are pregnant, the smaller your baby will be,’ which means the womb is no longer a nurturing environment," Hayes said.

The nine-pesticide combo also damaged the thymus, a part of the immune system, causing 70 percent of frogs to develop flavo-bacterial meningitis. The pesticides atrazine and S-metolachlor, which are marketed as the combination Bicep II Magnum, caused the most thymic damage.

To investigate why, Hayes and his laboratory colleagues, mostly undergraduate students, raised larvae of the common laboratory frog, the African clawed frog (Xenopus laevis), in water containing these pesticides and found four times the normal level of the stress hormone corticosterone. Hayes suspects that not all of the pesticides affect frogs, but that some enhance or trigger the deleterious effects of others when combined.

"Estimating the ecological risk and the impact of pesticides on amphibians using studies that examine single pesticides at high concentrations only may lead to gross underestimations of the role of pesticides in amphibian declines," he wrote.

In a second study also published online last week in Environmental Health Perspectives, Hayes reported even stronger evidence that atrazine, a powerful endocrine disruptor, both chemically castrates male frogs by blocking the action of the male steroid androgen and feminizes them by stimulating the production of the female hormone estrogen. He was able to produce identical hermaphroditic malformations in frogs by administering estrogen or blocking androgen at the proper time of development.

"One week of exposure at the critical time is all that’s required to make these males look feminine, which probably interferes with mating," he said. Noting that some frogs seem to adapt to atrazine by delaying development, presumably so that the critical developmental period takes place when the herbicide is at its lowest, Hayes suspects that not all frogs would be expected to adapt, or to adapt quickly enough, to survive. Plus, delayed maturation comes at the risk of having the pond turn into a puddle and dry up before the frog completely metamorphoses.

Hayes is continuing his studies with various combinations of pesticides to determine which are the true cause of the problem and which serve to enhance the effect of others.

His laboratory colleagues were UC Berkeley students Paola Case, Sarah Chui, Duc Chung, Cathryn Haefele, Kelly Haston, Melissa Lee, Vien Pheng Mai, Youssra Marjuoa, John Parker and Mable Tsui. Co-authors on the atrazine paper were former UC Berkeley students A. Ali Stuart, Atif Collins, Nigel Noriega, Aaron Vonk, Gwynne Johnston and Dzifa Kpodzo, and current students Magdalena Mendoza and Roger Liu.

The work was supported by the National Science Foundation, Henry H. Wheeler, the Park Water Co. and the Howard Hughes Biology Scholar’s Program.

Robert Sanders | EurekAlert!
Further information:
http://www.berkeley.edu

More articles from Life Sciences:

nachricht The irresistible fragrance of dying vinegar flies
16.08.2017 | Max-Planck-Institut für chemische Ökologie

nachricht How protein islands form
15.08.2017 | Albert-Ludwigs-Universität Freiburg im Breisgau

All articles from Life Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Exotic quantum states made from light: Physicists create optical “wells” for a super-photon

Physicists at the University of Bonn have managed to create optical hollows and more complex patterns into which the light of a Bose-Einstein condensate flows. The creation of such highly low-loss structures for light is a prerequisite for complex light circuits, such as for quantum information processing for a new generation of computers. The researchers are now presenting their results in the journal Nature Photonics.

Light particles (photons) occur as tiny, indivisible portions. Many thousands of these light portions can be merged to form a single super-photon if they are...

Im Focus: Circular RNA linked to brain function

For the first time, scientists have shown that circular RNA is linked to brain function. When a RNA molecule called Cdr1as was deleted from the genome of mice, the animals had problems filtering out unnecessary information – like patients suffering from neuropsychiatric disorders.

While hundreds of circular RNAs (circRNAs) are abundant in mammalian brains, one big question has remained unanswered: What are they actually good for? In the...

Im Focus: RAVAN CubeSat measures Earth's outgoing energy

An experimental small satellite has successfully collected and delivered data on a key measurement for predicting changes in Earth's climate.

The Radiometer Assessment using Vertically Aligned Nanotubes (RAVAN) CubeSat was launched into low-Earth orbit on Nov. 11, 2016, in order to test new...

Im Focus: Scientists shine new light on the “other high temperature superconductor”

A study led by scientists of the Max Planck Institute for the Structure and Dynamics of Matter (MPSD) at the Center for Free-Electron Laser Science in Hamburg presents evidence of the coexistence of superconductivity and “charge-density-waves” in compounds of the poorly-studied family of bismuthates. This observation opens up new perspectives for a deeper understanding of the phenomenon of high-temperature superconductivity, a topic which is at the core of condensed matter research since more than 30 years. The paper by Nicoletti et al has been published in the PNAS.

Since the beginning of the 20th century, superconductivity had been observed in some metals at temperatures only a few degrees above the absolute zero (minus...

Im Focus: Scientists improve forecast of increasing hazard on Ecuadorian volcano

Researchers from the University of Miami (UM) Rosenstiel School of Marine and Atmospheric Science, the Italian Space Agency (ASI), and the Instituto Geofisico--Escuela Politecnica Nacional (IGEPN) of Ecuador, showed an increasing volcanic danger on Cotopaxi in Ecuador using a powerful technique known as Interferometric Synthetic Aperture Radar (InSAR).

The Andes region in which Cotopaxi volcano is located is known to contain some of the world's most serious volcanic hazard. A mid- to large-size eruption has...

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

Call for Papers – ICNFT 2018, 5th International Conference on New Forming Technology

16.08.2017 | Event News

Sustainability is the business model of tomorrow

04.08.2017 | Event News

Clash of Realities 2017: Registration now open. International Conference at TH Köln

26.07.2017 | Event News

 
Latest News

New thruster design increases efficiency for future spaceflight

16.08.2017 | Physics and Astronomy

Transporting spin: A graphene and boron nitride heterostructure creates large spin signals

16.08.2017 | Materials Sciences

A new method for the 3-D printing of living tissues

16.08.2017 | Interdisciplinary Research

VideoLinks
B2B-VideoLinks
More VideoLinks >>>