Atrazine levels threaten frog populations

A recent US study established that levels of atrazine as low as 0.1 µg/litre (equivalent to 0.1 parts per billion) in water are sufficient to demasculinise frogs(1). An analysis performed by the Environment Agency shows that 10 sites in England and Wales had concentrations of atrazine higher than this between March and June 2000. Computer modelling predicted a further 13 catchment sites affected. 

Atrazine is one of the most widely used herbicides in the US and worldwide. Certain crops (most importantly maize) are tolerant of its effects and consequently atrazine is used to control weeds in these fields. However, there has been considerable concern over atrazine both due to its persistence in groundwater and soil, and to its potential to damage human health and the environment(2). 
    The major health and environmental concerns over atrazine are due to its ability to interfere with a range of hormone systems(3). Most studies document effects on sexual development and the ability to reproduce. While these studies are convincing they have mainly used high concentrations of atrazine. This has left uncertainty over whether atrazine can be detrimental at the concentrations normally found in the environment and in drinking water (3 µg/litre is the maximum for drinking water in the US).
    A new laboratory study carried out in the US found that atrazine can influence fundamental biological processes at concentrations much lower than previously thought. Tadpoles of the South African clawed frog, Xenopus laevis, were allowed to develop in different concentrations of atrazine and the effects studied. Concentrations as low as 0.1 µg/litre (30 times lower than the maximum allowed in US drinking water) were found to cause hermaphroditism (animals had both male and female sex organs) and concentrations of 1 µg/litre reduced the size of the male vocal organ which is vital to the frog mating ritual. The same effects have been found in wild frogs from six different locations in the Midwest(4). It is not hard to imagine that both these effects could significantly impair the ability of these frogs to breed. 
    Maize is grown extensively in the US, particularly in the Midwest where atrazine usage is so heavy that concentrations in rainwater can exceed 40 µg/litre(5). Even in areas where atrazine is used infrequently it has been detected in rainwater at 1 µg/litre. Most atrazine is applied in the spring and consequently is most concentrated in rainwater at this time. This is also the time when tadpoles are developing and so is the most sensitive time for frog populations. 
    Use of atrazine in the UK is considerably less than in the US. However, it increased from 24,120 spray hectares in 1989, to 109,602 spray hectares in 1997(6). The Environment Agency regularly monitor the concentrations of pesticides in rivers. They have a number test sites distributed throughout England and Wales and in addition have designed a computer-modelling programme Prediction of Pesticides Pollution in the Environment (POPPIE), which can predict likely concentrations for different catchment areas. In response to this new study they have reanalysed their monitoring data for spring 2000, the time when tadpoles are developing. They have found concentrations of atrazine exceeding 0.1 µg/litre at 10 sites. In addition, POPPIE modelling predicts concentrations exceeding 0.1 µg/litre at an additional 13 sites. While frogs prefer to breed in still waters such as ponds, the levels in rivers may be indicative of the concentrations that could be found at breeding sites.
    Amphibian populations have been declining worldwide and the UK is no exception. There are likely to be many different factors influencing this decline including disease and climate change. This study presents us with compelling evidence that use of herbicides such as atrazine could be contributing to this decline. 
    Atrazine use is currently being reviewed by the EU. The Pesticide Action Network are alarmed at the implications of this study. We call upon the EU to carefully consider these new data and to ban the use of atrazine in Europe. (RM)

References
1. Hayes, T.B., Collins, A.C., Lee, M., Mendoza, M., Noriega, N., Stuart, A.A. and Vonk, A., Hermaphroditic, demasculinized frogs after exposure to the herbicide atrazine at low ecologically relevant doses. Proceedings of the. National Academy of Sciences of the USA, 2002, 99 (8): 5476-5480.
2. Cox, C., Atrazine, Global Pesticide Campaigner, 2001, 11 (3): 18-25.
3. Cox, Ibid.
4. Dalton, R., Frogs put in the gender blender by America’s favorite herbicide, Nature, 2002, 416: 665-666. 
5. Dalton, Ibid.
6. Pesticides 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. 57, September 2002, page 10]