Cameo

Kermit to Kermette? by Frank J. Dinan

Part III—More from Hayes

Shortly after the work that we considered in Part II of this case study was reported, Hayes published a study in which he used a species of frog (Rana pipiens) that he collected in the wild at a variety of sites in the Midwestern U.S. (Hayes, 2003). In this study, Hayes used sales figures for atrazine in the various collection regions to estimate the extent to which the sites were likely to be contaminated with atrazine. The graph shown below compares the percent of frogs having gonadal abnormalities to the experimentally measured atrazine concentration in the water at each site.

Figure 6

Measured atrazine concentration present at each site in parts per billion (micrograms per liter): S1, 0.14; S2, 0.20; S3, 0.20; S4, 0.30; S5, 0.80; S6, 0.70; S7, 0.5

Both Hayes (Hayes, 2003) and a Syngenta supported group (Hecker, 2003) conducted laboratory studies to determine whether the testosterone level in the blood of male frogs was altered by the presence of atrazine in the water in which they grew. In these studies, larvae were grown until they reached sexual maturity in water containing an atrazine concentration of 25 ug/L. For control purposes, both of these studies grew larvae in water containing a nominal (supposed) atrazine concentration of zero ppb. The graph shown below indicates the results obtained in the two studies:

Figure 7

In its evaluation of the data reported in the MSU (Hecker) study, the EPA noted that the controls used in this study were not free of atrazine but were in fact found to contain “atrazine at levels comparable to those in the 0.1 ppb treatment level” (Steeger, 2003). No atrazine was found in the controls used in the Hayes study (Hayes, 2004).

Questions

  1. What do the Hayes results indicate about the effect of atrazine on the testosterone concentration in the blood of exposed male frogs?
  2. What do the MSU results indicate about the effect of atrazine on the testosterone concentration in the blood of exposed male frogs?
  3. Consider the EPA’s observation about the presence of atrazine in the controls used in the MSU study. Could this observation explain how Hayes and Hecker could both have accurately reported their experimental observations?
  4. In 2003, the EPA recommended that Syngenta’s license to continue the use of atrazine in the United States be approved. If one assumes that the data presented here are valid, what factor or combination of factors might have led to this recommendation?
  5. Search for two web sites that support the continued use of atrazine and two web sites opposed to its continued use. Prepare an assessment of the validity of these web sites and be prepared to share your observations in class. Useful guidelines for the evaluation of the credibility of web postings may be found at the following URL:
    http://www.virtualchase.com/quality/checklist_print.html.

References

Agency for Toxic Substances and Disease Registry, Centers for Disease Control, 2003, “ToxFAQs for Atrazine.”
http://www.atsdr.cdc.gov/tfacts153.html. Last accessed: 2/17/06.
Carr J. A., et al. 2003. Response of larval Xenopus laevis to atrazine: assessment of growth, metamorphosis, and gonadal and laryngeal morphology. Environmental Toxicology and Chemistry 22(2): 396–405.
Hayes, T. B, et al. 2002. Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses. Proceedings of the National Academy of Science 99(8): 5476–80.
Hayes, T. B., et al. 2003. Atrazine-induced hermaphroditism at 0.1 ppb in American leopard frogs (Rana pipens): laboratory and field evidence. Environmental Health Perspectives 111(4): 568–73.
Hayes, T. B. 2004. There is no denying this: defusing the confusion about atrazine. Bioscience 54(12): 1138–49.
Hecker, M. J., et al. 2003. Response of Xenopus laevis to atrazine exposure: assessment of the mechanism of action of atrazine. Ferndale, WA. Ekorisk, Interim Report MSU-04 (in Hayes 2004).
Steeger, T. M. 2004. Data evaluation report on the response of Xenopus laevis to atrazine exposure: assessment of mechanism of action of atrazine. EPA MRID no. 458677-04 (10 November 2004).
http://www.epa.gov/oscpmont/sap/2003/june/dataevaluationreports.htm. Last accessed: 2/17/06.


Originally published at http://www.sciencecases.org/kermit/kermit3.asp

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