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Croaking it - a new threat from atrazine

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In this International Year of the Frog, Dr Arthur White outlines some disturbing evidence about declining frog populations in agricultural areas, and, whilst the setting is the United States of America, the ramifications will be felt around the world.
Pesticides and frogs have a chequered history, beginning with the wonder pesticide known as DDT. From the 1930s to the 1960s DDT was the mainstay (and main spray) of broad scale agricultural production and it was so effective against insect pests that widespread crop dusting was a feature of its use. Unfortunately DDT, used indiscriminately, also entered water sources and now has a reputation as one of the “dirty dozen”, organochlorides that do not break down in soil and stay poisonously active for long periods. The disappearance of frogs was one of the many alarm bells that alerted people to the possible bad side effects DDT, the others being the rise of illness, death, sterility and malformed babies, especially notable in the farm belt of the American Midwest. The evidence was insurmountable and DDT was eventually banned in many countries.

Then along came another organochloride, atrazine. Extensively tested in laboratories at spray concentration levels, atrazine showed no effects on frogs or other aquatic organisms. It also effectively killed all target insects and broke down quickly in the soil. Scientifically, it was given the green light, was widely taken up and used in modern broad scale agriculture and was thought to be the answer that farmers were looking for. Everyone was content until…

A few years ago frog fieldworkers in the USA noticed that frog populations were declining in areas where atrazine was used and in some areas, frogs had disappeared altogether.

Puzzled, they began testing frog tissues. This testing revealed some organ malfunctions and one startling and totally inexplicable surprise - virtually ALL of the frogs tested by this random sampling method were male!
Disturbed, they tested for the presence of atrazine which was found to be in the tissue at incredibly low levels and also found to be also present in the water at levels almost impossible to detect.

Above: Rana pipiens - the first frog in the USA shown to be affected by atrazine, with disappearing populations and others where only males were found. Photo from Arthur White.     

It was clear that further testing was required, so atrazine-free tadpoles were introduced into water with trace amounts of atrizine. All of the tadpoles became male and all had secondary, minor organ damage. These extraordinary results were further tested at various universities including the Universities of California and Berkeley, where it was discovered that, at very low dosage levels, atrazine interferes with sexual hormone production.

Whilst previously tested high spray concentrations showed no ill effects on frogs, these very low concentrations can go undetected by the frog's immune system with devastating consequences.
Right: atrazine is not the only insecticide to impact on frogs.  The tumour shown on an Australian tree frog is typical of the effects observed in Australian agricultural areas. Photo from Arthur White.

Obviously the defence mechanisms of other vertebrates needed to be tested, including people.  In the midwest agricultural region of the USA where atrazine was found to be affecting frogs, researchers workers have trawled through case studies, records of births and deaths, as well as testing local water sources. While there has been no change in the sex ratio for the human population in the areas, since the commencement of use of atrazine, some communities have showed increasing rates of miscarriage that are now ten times higher than the national average.  In addition, it has also been established that active sperm rates in the male population are as low as 1% in designated areas.


Clearly the manufacturers are not impressed and some of their own research has failed to replicate the findings of atrazine as a harmful substance. It is still not banned anywhere in the world but all eight independent studies so far conducted by American universities all point the finger at the poisoned chalice laced with atrazine.

Atrazine is used widely in Australia and it can only be hoped that the findings in the USA will spur on the rapid and generous allocation of research funds before we have an amphibian replication of the Silent Spring!

Text: V.B. Feb 2008   

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