DDT environmental effects

By Allison Jess
October 11 2007;  Australian Broadcasting Company
http://www.abc.net.au/goulburnmurray/stories/s2054547.htm

The use of DDT or Dichlorodiphenyltrichloroethane has been banned in Australia since 1987. Twenty years on, Glen Johnson from the Department of Sustainability and Environment says its effects are still being felt on the environment.

Johnson says DDT was used in Australia as an insecticide. "It's got an interesting history. It was first produced back in the 1800's and came to the fore just around and prior to the war years. It was used by the U.S. on its army because they had lots of head lice and body lice issues with their soldiers overseas. It was used from about that 1943 period onwards in the States and a little bit earlier in other countries."

"It obviously has had a huge beneficial impact from controlling of malaria and other agricultural pests so it was widespread in its use and probably at its peak in the 1960's when there was 80 million kilograms being produced and used annually. Johnson says during that time it evolved from a pest control to being used for broader agricultural applications.

Johnson says it was shortly after the end of the Second World War that the U.S. Fish and Wildlife Service started to express their concerns of DDT in literature; "At that stage Brown Pelicans dramatically declined and there was a decline in the Bald Eagle population almost to extinction."

"It's in those species which are perhaps at the higher end of the food chain where there is this magnificent term called bio-cumulation that occurs. What happens is there is a gradual accumulation of the pesticide in prey items that are then accumulated and absorbed into the fatty tissues of animals. So particularly things like whales and dolphins that have got large fatty tissues, they end up storing and accumulating a concentrated amount over time that is way beyond the external environmental levels at that time. There have been things associated with wildlife in Australia such as Peregrine Falcons and a whole raft of other species due to egg shell thinning. This resulted in the loss of reproductive output from a whole range of animals so it's been pretty dramatic right throughout the world."

Johnson says pesticides such as DDT's are long lived and have a long half-life. "Perhaps up to half a century on some and they are highly toxic and have the ability to persist and spread throughout the environment. For instance in the Arctic and Antarctic where we haven't had the application of some of these things, they are nevertheless in the environment. They are spread by the air and water and do end up in places where they weren't originally applied and have an extremely long potency period."

"Some people might remember The Silent Spring by Rachel Carson in 1962; it was an incredible document at that time which illustrated these concerns. Around that time there was a recognition of concerns and a lot of these were put into long term dumps and it's now unfortunate that some of these historical dumps from Russia and through other parts of the world are breaking down and being mobilised in the waterway systems; it's quite a pronounced long term problem."

However twenty years since its ban in Australia, Johnson says there are signs of recovery from the effects of DDT; "There has been a dramatic increase in the reproductive success of a whole range of birds like Peregrine Falcons in Australia."