atrazine and the threat to frogs

[jcummins <jcummins@UWO.CA>]

The article below deals with the threat of continued atrazine use. 
Interestingly, even though atrazine resistant crops and weeds are 
appearing there have been no commercial GM  atrazine resistant crops. 
Here-to-fore GM atrazine resistant crops experience significant yield 
decline but that problem may soon be overcome by genetic engineers. 
Atrazine is one of the most inexpensive herbicides to employ and a real 
temptation to genetic engineers (an application that must be prevented 
at any cost).
Nature 419, 895 - 896 (2002); doi:10.1038/419895a

Herbicides: Feminization of male frogs in the wild

Water-borne herbicide threatens amphibian populations in parts of the 
United States.

Atrazine is the most commonly used herbicide in the United States and 
probably in the world1. Here we investigate the effects of exposure to 
water-borne atrazine contamination on wild leopard frogs (Rana pipiens) 
in different regions of the United States and find that 10–92% of males 
show gonadal abnormalities such as retarded development and 
hermaphroditism. These results are supported by laboratory observations, 
which together highlight concerns over the biological effects of 
environmental atrazine on amphibians.

We exposed R. pipiens larvae to different concentrations of atrazine (0, 
0.1 or 25 parts per billion, p.p.b.) in the laboratory by immersion (30 
larvae per treatment; n = 3) from just after hatching until tail 
resorption was complete. Only exposed males developed testicular oocytes 
(29% and 8%, respectively, at 0.1 and 25 p.p.b.); retarded gonadal 
development (gonadal dysgenesis) was evident in 36% and 12% of exposed 
males, respectively, and in one control animal (results not shown).

These findings are consistent with the more marked effects reported for 
endocrine-disrupters at lower doses (see ref. 2, for example). They also 
support previous indications that atrazine can cause gonadal 
abnormalities in males of Xenopus laevis3, 4 and Acris crepitans5 in the 
laboratory. As its effects are not restricted to a single species, it is 
possible that this herbicide may pose a threat to amphibians in general.

We also examined leopard frogs, sampled from eight different sites in a 
transect running from Utah to Iowa, for abnormalities comparable to 
those seen under laboratory conditions. We used records of atrazine 
sales to identify potentially contaminated sites (Fig. 1). As control 
sites, we used various non-agricultural regions in Utah, Wisconsin and 
Nebraska that reported atrazine sales of less than 0.4 kg km-2, as well 
as a non-agricultural area in Iowa. A golf-course pond in Cache county, 
Utah (the only county reporting atrazine sales of more than 0.4 kg 
km-2), and cornfields in Nebraska and Iowa were considered to be likely 
sites of contamination. Water sampling revealed that only one site (Juab 
county, Utah) had atrazine levels below our detection limit (0.1 p.p.b.).

Figure 1 Use of the herbicide atrazine in the United States, on the 
basis of sales11.   Full legend

High resolution image and legend (74k)

This site was the only locality where testicular oocytes were not 
observed in the local population of leopard frogs. All sites associated 
with atrazine sales exceeding 0.4 kg km-2 and with water-borne atrazine 
contamination above 0.2 p.p.b. were found to contain males with 
testicular oocytes (Fig. 2a, b). These abnormalities were of similar 
morphology to those induced by atrazine in the same species in the 
laboratory. This hermaphroditism was not evident in the absence of 
atrazine exposure. We conclude that atrazine is responsible for these 
effects in wild populations, even though other contaminants may be 
present that could produce similar effects.

Figure 2 Testicular oogenesis in wild leopard frogs.   Full legend

High resolution image and legend (29k)

Atrazine may affect sex differentiation by inducing aromatase, the 
enzyme that converts androgens into oestrogens, and can cause 
inappropriate synthesis and secretion of oestrogens in males at the 
expense of androgens. This occurs in fish6, reptiles7 and mammals6, 8, 
with inhibition of spermatogenesis probably being a secondary effect 
associated with the depletion of androgens and synthesis of oestrogens 
in exposed males, rather than a direct effect of atrazine. Evidence for 
this mechanism of toxicity in three out of five vertebrate classes, and 
possibly in amphibians as well, generalizes the possible environmental 
risk associated with atrazine.

Most water sources in the United States, including rain, contain more 
atrazine than the effective doses determined in laboratory studies1. 
Although the locality in Wyoming (North Platte River) with the highest 
frequency of sex reversal (92% of males) is not in the vicinity of farms 
and is not in a county that reports significant atrazine usage, 
hermaphrodite frogs are prevalent there because the North Platte River 
is fed by atrazine-contaminated9 streams that originate in Colorado.

The frequency of abnormalities at site 2 is much lower than at site 3, 
although the contamination measured at these sites was comparable. It 
may be that intermittently exposed populations are more susceptible to 
atrazine-induced hermaphroditism, whereas continuously exposed 
populations undergo adaptive resistance.

Applied to crop fields as a pre-emergent, atrazine contamination in 
water sources peaks with spring rains, which also coincide with breeding 
activity in many amphibians. Given the adverse effects of atrazine on 
the gonads of male frogs, this pattern of atrazine application may 
increase its impact on amphibian populations. In the light of growing 
evidence that these populations are in decline10, the contribution of 
atrazine to this decline warrants further investigation.

TYRONE HAYES, KELLY HASTON, MABLE TSUI, ANHTHU HOANG, CATHRYN HAEFFELE & 
AARON VONK
Laboratory for Integrative Studies in Amphibian Biology, Museum of 
Vertebrate Zoology, and Department of Integrative Biology, University of 
California, Berkeley, California 94720-3140, USA

e-mail: tyrone@socrates.berkeley.edu
------------------

References
1. US Environmental Protection Agency. Federal Register 59, 60412-60443 
(1994).
2. Akingbemi, B. T. & Hardy, M. P. Ann. Med. 33, 391-403 (2001). | PubMed |
3. Hayes, T. B. et al. Proc. Natl Acad. Sci. USA 99, 5476-5480 (2002). | 
Article | PubMed |
4. Tevera-Mendoza, L. et al. Environ. Toxicol. Chem. 21, 527-531 (2002). 
| PubMed |
5. Reeder, A. L. et al. Environ. Health Perspect. 106, 261-266 (1998). | 
PubMed |
6. Sanderson, J. T., Letcher, R. J., Heneweer, M., Giesy, J. P. & van 
den Berg, M. Environ. Health Perspect. 109, 1027-1031 (2001). | PubMed |
7. Crain, D. A., Guillette, L. J. Jr, Rooney, A. A. & Pickford, D. B. 
Environ. Health Perspect. 105, 528-533 (1997). | PubMed |
8. Sanderson, J. T., Seinen, W., Giesy, J. P. & van den Berg, M. 
Toxicol. Sci. 54, 121-127 (2000). | Article | PubMed |
9. Kimbrough, R. A. & Litke, D. W. Pesticides in Surface Water in 
Agricultural and Urban Areas of the South Platte River Basin from 
Denver, Colorado to North Platte, Nebraska, 1993-94 (NAWQA Program, 
South Platte River Basin Study, Denver, Colorado, 1995).
10. Wake, D. B. Science 253, 860 (1991).
11. Battaglin, W. A. & Goolsby, D. A. Water-Resources Invest. Rep. 
94-4176 (US Geol. Surv., Denver, Colorado, 1995).
12. Stebbins, R. A Field Guide to Western Reptiles and Amphibians: Field 
Marks of All Species in Western North America, Including Baja California 
(Houghton-Mifflin, Boston, 1985).
13. Conant, R. A Field Guide to Reptiles and Amphibians: Eastern and 
Central North America (Houghton-Mifflin, Boston, 1998).

.