Atrazine water menace

Dramatic decreases in frog populations have been documented by wildlife biologists for several decades. A new US field study provides compelling evidence that the widely used herbicide atrazine is playing a significant role in this decline(1). 

Northern leopard frog Photo: Brad Shaffer

A recent laboratory study found feminising effects of atrazine on male frogs (see PN 57 p16). In this study Tyrone Hayes, a researcher at the University of California, allowed tadpoles of the ‘lab frog’ Xenopus laevis to develop in different concentrations of atrazine (0, 0.1, or 25 parts per billion). Even the lowest concentration used in his study (0.1 parts per billion) was able to feminise male frogs. Feminised males had smaller voice organs than normal and had ovary tissue in their testes. Although the ability of atrazine to impair sexual development had been documented before, this study observed effects at concentrations much lower than those observed previously and at concentrations routinely found in the US environment.

Startling findings
While this study clearly sounded alarm bells it also left two major questions to be answered. Are other frog species as sensitive to atrazine, or is this effect an anomaly of X. laevis? If these effects occur at atrazine concentrations lower than those found in many areas of the US can we find affected wild frogs at these locations?
    Professor Hayes has now published his latest research which answers both of these questions. He has carried out a laboratory study on the leopard frog, Rana pipiens. As before he allowed tadpoles to develop in 0, 0.1 or 25 parts per billion atrazine, and observed the same dramatic effects at even the lowest concentration of atrazine. Atrazine-treated males (0.1 and 25 ppb) suffered from under-developed testes (36% and 12% respectively), and also suffered from sex reversal, in particular the presence of ovary tissue in the testes (29% and 8% respectively).
    Leopard frogs are one of the most common native frogs in the US and the ability of atrazine to feminise the males of this species at such low levels is quite startling. The effective concentration in this study (0.1 ppb) is 30 times lower than the drinking water standard in the US (3 ppb), and atrazine usage in the US is so widespread that ground and surface waters exceed this concentration in most areas(2). 
    Armed with knowledge about the types of defects caused by atrazine in the laboratory Professor Hayes collected 100 leopard frogs from each of eight sites located in a transect across the US. He studied the male frogs to determine whether any carried defects similar to those caused by atrazine in the laboratory. The results were astounding. Between 10% and 92% male leopard frogs were found to be feminised depending on the site, and the abnormalities exhibited by the frogs were the same as those caused by atrazine in the lab. The only site where no effects were noted was a site chosen as a control on the basis of low atrazine sales figures (less than 0.4 kg/km2), and also was the only site with atrazine concentrations below the 0.2 ppb at the time the frog were collected.
    Atrazine has been the subject of controversy for over a decade. The United States Environmental Protection Agency initiated a special review of the triazine herbicides, including atrazine, simazine, and cyanazine in November 1994, a process only initiated when there are particular concerns about human or environmental health. Their initial focus was on the possibility that atrazine could cause cancer but these concerns have since been supplemented by an increasing number of studies pointing to the impact of atrazine on sexual development. 

Manufacturer casts doubt 
Syngenta, one of the main manufacturers of atrazine is keen to see its products re-registered at the end of the EPA’s special review next year. They, and a number of researchers funded by them, have voiced criticisms of Hayes’s work. Firstly, they suggest that hermaphroditism is a natural phenomenon and argue that the effects Hayes observed in the field may also be natural. They cite a 1929 study documenting hermaphrodites of frog Rana temporaria(3). While it is likely that frog hermaphrodites occur at a low frequency in natural populations (as they do indeed in human populations), according to Hayes ‘it is extremely unlikely they would occur at the frequencies observed in this study’. Perhaps more importantly the precise defects caused by atrazine in the laboratory and observed by Hayes in wild caught leopard frogs are quite distinct from those documented in natural R. temporaria hermaphrodites. 
    Secondly, they cite the work of Professors Carr and Smith at Texas Tech University who carried out a similar study but were unable to reproduce the low dose effects on the vocal organs and testes. Hayes is critical of their attempts to reproduce his work pointing out that in the Carr and Smith study frogs were overcrowded and underfed, and the majority failed to metamorphose within 80 days, a sign of stress. In addition, rather than completely refreshing the water plus atrazine mix in the tank every three days (as in the Hayes study), they only refreshed a portion each time. Hayes believes this resulted in a gradual dilution of the atrazine concentrations(4). 

Atrazine in the UK and Europe
In the UK atrazine is the pesticide most frequently found contaminating groundwater(5). Concern about this led to a ban on its use on non-cropped land in 1992 (except for home and garden use). The numbers of groundwater samples contaminated with atrazine have declined since then; however, there are areas of the country where atrazine contamination still persists (see PN 57, p16). These sites are likely to be associated with agricultural and horticultural uses of atrazine, some of which have increased(6). 
    Frogs and other amphibians may be particularly sensitive to environmental contaminants. Their lifestyle, partly in water and partly on land, makes them susceptible to both waterborne and to airborne contamination and they are regarded by many as sentinels of harm that could affect human populations. Atrazine has already been banned in several countries in Europe (Sweden, Austria, Slovenia, Italy, Germany, Denmark and Norway) and is not registered for use in several others. PAN UK calls upon the UK government to consider these new studies and ban all uses of atrazine. (RM)

References
1. Hayes T, Haston K, Tsui M, Hoang A, Haeffele C, Vonk A, Feminisation of male frogs in the wild, 2002, Nature 419, 895-6; Hayes T, Haston K, Tsui M, Hoang A, Haeffele C, Vonk A, Atrazine-induced hermaphroditism at 0.1 ppb in American leopard frogs (Rana pipiens): Laboratory and Field Evidence. Environmental Health Perspectives, doi:10.1289/ehp.5932 (available at http://dx.doi.org).
2. Hayes TB, Collins AC, Lee M, Mendoza M, Noriega N, Stuart AA, and Vonk A, Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses, Proceedings of the National Academy of Sciences U.S.A., 2002, 99, 5476-5480.
3. Witschi E, Rudimentary hermaphroditism and Y chromosome in Rana temporaria, Journal of Experimental Zoology 54, 157-223, 1929.
4. Hayes T, pers comm., 9 December 2002.
5. Pesticides in the Aquatic Environment 1997. Environment Agency, 1999.
6. Pesticide Usage Survey Report, Grassland and Fodder Crops, Number 151, ministry of Agriculture, Fisheries and Food and Scottish Office Agriculture, Environment and Fisheries Department, 1997.

[This article first appeared in Pesticides News No. 58, December 2002, page 19]