No defence

Frogs’ immune systems affected by pesticides

source: Kurt Kleiner
New Scientist May 4 2002 p12

Frogs’ immune systems can be affected by small amounts of pesticides, according to Brian Dixon from Canada’s University of Waterloo, Ontario. He injected DDT, dieldrin and malathion into northern leopard frogs, and discovered that their antibody production fell dramatically, sometimes to zero, following these injections, which were nearly as powerful as immunosuppressants as a drug used for this purpose, cyclophosphamide.

Dixon also studied wild frogs in polluted locations in Ontario. These frogs suffered the same sort of immune system damage as the injected froms, and the psticide levels are similar. Canada has banned usage of dieldrin and DDT, but these pesticides break down slowly, while malathion is still in use.

The wild frogs were still able to produce antibodies in response to antigens they had been in contact with prior to their exposure to pesticides, and they also underwent some recovery eight weeks after a transfer to clean water.

These findings, which are to be published in Environmental Toxicology and Chemistry, may help explain a world-wide drop in frog numbers. Affected frogs may also be more susceptible to infection by parasites.