New Scientist 27 June 1998 4: An unnamed primitive fungus of the chytrid genus has struck down 10 Australian frog species and may be affecting the world amphibian populations. It could also be spread by frog ecologists seeking to protect species.
Frog song New Scientist 14 Feb 98
Are agricultural chemicals poisoning amphibians?
THE worldwide decline in amphibians has perplexed researchers for more than a decade. It has been blamed on many things, including synthetic chemicals, viral infections and the thinning of the ozone layer (This Week, 13 September 1997, p 18). Now a Swiss study on the effect of fungicides on tadpoles suggests that agricultural chemicals may be a major culprit. A team led by Heinz-Ulrich Reyer of the Zoological Institute at the co University of Zurich has found that triphenyltin, which is used as a fungicide, causes deformity and death in several species of frog even at concentrations below those found around farmland. The findings are published in Environmental Toxicology and Chemistry (vol 16, p 1940). Triphenvltin is mainly used to control blight in sugar beet and potatoes, but is also used on celery, carrots, onions, rice, pecan nuts, peanuts, hops and coffeeand in antifouling paints for ships. It has contaminated many aquatic environments, either directly as in rice fields, or as runoff when it flows into ditches, lakes and temporary pools. Triphenyltin degrades slowly in water and has been shown to be highly toxic to a range of aquatic organisms, from dragonfly larvae and snails to fish. Earlier research had found triphenyltin concentrations of up to 0.2 micrograms per litre in harbours and rivers, and up to 146 micrograms per litre in rice fields. The Swiss team subjected tadpoles of two species of water frogs (Rana lessonae and R. ridibunda) and various hybrids to concentrations ranging from 0.09 to 1.82 micrograms per litre. They found that not only did the tadpoles' Iffe spans shorten, but they also grew more slowly and took longer to reach metamorphosis. Their swimming and feeding were severely affected. The researchers believe that the chemical disrupts tadpoles' central nervous systems. The higher the concentration of fungicide, the worse the damage. For amphibians, any delay in development is especially hazardous since it makes them more vulnerable to predators. Reyer believes the damage could drive local frog populations to extinction. Tim Halliday, international director of the World Conservation Union's working group on amphibians, says the Swiss study may provide an explanation for amphibian decline at a local level. 'But it doesn't help to explain it on a bigger scale, or in pristine areas where chemicals are absent," he notes. Oliver Klaffke, Basel