Rigor Vitae: Life Unyielding

Friday, February 17, 2006


In a recent post, I discussed some of the factors implicated in the current startling global decline of frogs. In two papers in the February edition of the online journal Environmental Health Perspectives, Tyrone Hayes and his colleagues, of UC Berkeley, have added some interesting new pieces to the puzzle.

The first paper provides strong evidence that, while tiny concentrations of many chemical pesticides have deleterious effects on frogs, mixtures of the compounds may be far worse than the sum of their parts. In a four-year study which raised tadpoles of Northern Leopard Frogs (Rana pipiens) in water with various combinations of pesticides typical of waters near midwestern cornfields, mixtures showed far greater effects than did single chemicals. When a mixture of all nine chemicals (four popular herbicides, three insecticides and two fungicides) was present at 0.1 ppb (one of the lowest concentrations measured in the field), tadpoles took 30% longer to metamorphose, and a 35% mortality rate was measured. While the metamorphosis period was longer, the affected adult frogs were considerably smaller than average, making them dependent on new prey, and vulnerable to new predators. The pesticide cocktails also caused thymic damage, making the frogs particularly susceptible to bacterial meningitis. In a separate study of African Clawed Frogs (Xenopus laevius), the thymic damage was shown to be caused by elevated levels of the stress hormone corticosterone.

Hayes has studied the feminizing effect of minute concentrations of Atrazine, the most popular agricultural herbicide used in America, on male frogs for years. In his second paper, he shows further details of how the powerful endocrine disrupter blocks the effects of androgen, and stimulates estrogen production.
illustration: SOUTHERN LEOPARD FROG & TRICOLORED HERON (2000) acrylic 13.5" x 7"


Anonymous Anonymous said...

The best thing about the work Hayes is doing is his honesty. So many biologists are out to find evidence for a hypothesis, but Hayes has several times allowed as how the reality was far more complicated than he expected. Unfortunately, the complexity allows Syngenta, the manufacturer of atrazine, and other like-minded companies to delay real intervention so long as the jury is out. With the pandemic amphibian decline in high gear, I hope we're not going "all in" with these species as collateral.

11:48 AM  
Blogger Carel Brest van Kempen said...

I couldn't agree more, Hungry. Hayes is a good guy, and Atrazine a powerful nemesis. There's presently lots of well-funded research going on designed to make Atrazine appear innocuous.

3:06 PM  
Anonymous Anonymous said...

I can't get past the painting- absolutely incredible. Many folks could paint a frog, many could paint a heron- but you've captured a moment in time that few could accomplish with such intricate realistic details.
Off to read more in regards to ordering your book, I'm hooked on your artistry. They each breathe so much life, a rare gift.

7:02 PM  
Blogger Carel Brest van Kempen said...

Wow. Thanks, Cindy!

8:04 AM  
Anonymous Anonymous said...

Amen Cindy. This painting is knocking my socks off! CPBVK, you rock!

10:57 AM  
Blogger Carel Brest van Kempen said...

Thanks, Birdmeister!

10:34 AM  
Anonymous Anonymous said...

I know this is an old post, but I've been readin backwards. Aw, I really love your work. My eldest daughter, Meadow, is well...she's a nature lover. Her first fascination was with the frogs and I am so ignorant I had no idea they were declining. Anyway, we're home educating our children and use the web as a way of gathering some information about the subjects the children are into. Thanks for your site and your links...and we think sixty odd dollars is a small price to pay for your book (hmm and the leather bound edition would be more practical). Hope it goes well, and I'll link to your site from mine because it is soooooo impressive. Best wishes to you and good luck with the book - it looks like it deserves to be a success.

12:58 PM  
Blogger Carel Brest van Kempen said...

Thanks very much for your kind remarks, E.F.! I hope to live up to your expectations.

11:22 AM  

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