Tuesday, May 25, 2010

Atrazine still shown to be toxic to amphibians

Oddly, the post we’ve gotten the most comments on here is my atrazine article awhile back. So I figure now would be a good time to see if there have been any new research in support of or in opposition to atrazine’s (ATZ) toxicity to amphibians.

And in last month’s EHP ( I tend to stick to this journal for a lot of my posts since its readily available and deals with the “big” environmental issues that are easier to blog about) there was another paper linking atrazine exposure to sexual disruption in frogs. Interesting. So what makes this paper stand out? Well since a lot of the conflicting reports on ATZ toxicity are between laboratory studies this new paper analyzes a commercially prepared ATZ mixture and with exposure at environmentally relevant concentrations using outdoor mesocosms. And in addition, the study analyzed a native frog, R. pipiens, to the region where the study was performed. So from all that, looks like whatever the results might be, they will better mimic the potential toxic effects to amphibians compared to the laboratory results which have been so controversial. There were further lab exposures as part of this study but I’ll just focus on the mesocosms since I find that portion then most novel.

Using 100gallon containers furnished with leaves and other organics and filled with groundwater, tadpoles reared from locally collected egg mats were added to each mesocosm. ATZ was tested at a both 0.1ug/L and 1.8ug/L concentration and against 1.5ug/L 17α-ethinylestradiol (EE2) which serves as a positive control. ATZ concentrations tested were selected to mimic the concentration measured in the local river and streams (and it was detected in every stream tested) which ranged from 0.01-1.6ug/L. And even at these very low concentrations, tadpoles were affected by the presence of the herbicide. In the high concentration ATZ group, survival rate was significantly less compared to the control, 66% and 79% respectively. So that shows ATZ is toxic, but is it the notorious endocrine disruptor its made out to be?

There are some indications, that yes, ATZ exposure induces sexual disruption. The first being metamorphosis. Whereas 76% of control tadpoles achieved metamorphic success, only 45% of the low ATZ group and 50% of high ATZ group were successful. Surprisingly in this measurement, ATZ seems to be a more potent estrogen mimic compared to the positive control, in which 55% of EE2 treated tadpoles completed metamorphosis. Furthermore, the high ATZ group shifted the sex ratio to a female bias (1:1.4 male: female) while the control embryos exhibited a male bias population (1:0.6) which is comparable to sex ratios of adult frogs populations at the collection sites.

Now, here is where things get a little tricky and authors are sure to hedge their results. Unlike my last post on atrazine, no frogs from either ATZ treatment showed signs of intersex while 22% of EE2 treated frogs did. But differences between gonadal studies the authors suggest, may come down to differences in experimental design and choice of frog species tested. The authors also tested for a variety of gene expression and enzyme levels but many showed no difference from the control. Chronic low level ATZ exposure did however alter brain estrogen receptor activity and altered activity of liver enzyme that is thought to be related to feminization. These two changes may be responsible for the metamorphic interference observed, but it is still unclear.

So looks like atrazine will remain somewhat controversial. There have been some definite observations of function responses to environmentally relevant concentrations of ATZ but the mechanisms which induce endocrine disruption by way of ATZ cannot yet be confirmed. But, this study does offer a picture of real world chronic exposures which are experienced by amphibians. Atrazine, once again, has been shown to be toxic and should be of serious environmental concern.

Langlois VS, Carew AC, Pauli BD, Wade MG, Cooke GM, et al. 2009 Low Levels of the Herbicide Atrazine Alter Sex Ratios and Reduce Metamorphic Success in Rana pipiens Tadpoles Raised in Outdoor Mesocosms. Environ Health Perspect 118(4): doi:10.1289/ehp.0901418


  1. Since the 1950s, Atrazine has been favored in the fight against weeds that prevent abundant yields, or harvests. It also doesn't cause injury to crops and is adaptable to most soil systems. More than 65 percent of America's corn crops are treated with Atrazine. Herbicide workers also spray the chemical over highways and railroad paths.

  2. Except that doesn't address the issue of whether it's toxic. Just because something works incredibly well doesn't mean we should use it. PCBs worked great as coolants and insulators but you see how well that turned out.

  3. Life without atrazine would complicate weed management in corn, especially for sweet corn growers. A study at the University of Illinois looked at 175 sweet corn fields in the Midwest to find out just how important this 50-year-old, broad-spectrum herbicide is in sweet corn grown for processing.

  4. Three cheers for atrazine then for boosting sweet corn crop! Again, just because something is effective doesn't mean we should use it unquestionably. History has repeatedly shown, whether its CFC's or TEL or any other phased-out chemical, effectiveness can come at a serious environmental cost.

    Chemicals are being manufactured and incorporated into products at a rate that far exceeds the time it takes to perform thorough studies by environmental biologists,chemists and toxicologists (I guess these are those darn "eco-activists" mentioned in the link contained in your user name). So yes, some toxicity results are controversial for AZT - but the fact we can show toxic effects of AZT at environmentally relevant concentrations through multiple experimental designs should be signaling the alarms in your heads that, hey, maybe this isn't the best thing we should be spraying.

    In other words, don't come to this blog if you're just going to taut how extensively we use ATZ, because that's no excuse to not do anything nor is it a logical response to these scientific studies.

    Anyways, while doing some more ATZ research, I came across this old post* by Ed Yong that summarizes a study linking amphibian decline to ATZ exposure but through indirect means. ATZ altered local food webs allowing proliferation of parasites which in turn increased infection rates in amphibians. So this is not just direct toxicity we're dealing with. I'll have to read the paper when I get a chance.

    * http://scienceblogs.com/notrocketscience/2008/10/common_pesticide_is_good_news_for_parasites_bad_news_for_fro.php

  5. When using atrazine products, farmers in the United States are turning more to conservation tillage and no-till systems. In 2008, atrazine was applied to more than 60 percent of conservation tillage and no-till corn acres.

  6. /facepalm

    Why do I feel like I'm just getting automated responses from pro-atrazine groups.

  7. The report by the Natural Resources Defense Council released Tuesday shows the Big Blue River watershed in upper Gage County had the highest maximum peak concentration of atrazine of 20 watersheds in five farm states monitored in 2007 and 2008.