ENHS Nature Trails November 2002 Article 3

Frozen Fall, Silent Spring
by Reida Kimmel

The sight of our little pond completely frozen for four days has filled us all with amazement. Of course, with water levels lower than I have ever seen them, this freeze cannot compare with the really big freezes of winter when, in the old days, the pond was a magnet for neighborhood ice skaters. Still, the ice and the drought have made me worry about our resident frogs. Our "house frog," an otherwise ordinary Hyla that has learned to use the front door, has been silent for many weeks. I evicted him from our living room twice this summer and carefully placed him in the geraniums on the deck both times. The plants went into the greenroom well before the big frost, but as it is very cold in there now, we don't expect to hear his calls until spring. Still, it would be nice to catch a glimpse of him, just to know that he is all right.

Two papers which appeared in the Proceedings of the National Academy of Sciences this year, and which were discussed in our own local and excellent Journal of Pesticide Reform, published by the Northwest Coalition for Alternatives to Pesticides in the Summer and Fall 2002 issues, have made me think more globally about frogs. T.B.Hayes and his colleagues at Berkeley did very careful studies using African clawed frogs, Xenopus laevis, in the laboratory and discovered that the herbicide atrazine, which is probably the most commonly used herbicide in the world, causes exposed male tadpoles to become hermaphrodites because it boosts levels of the enzyme aromatase that normally converts testosterone into estrogen; thus, exposed frogs have lower testosterone levels and high estrogen levels (PNAS 99:5476-5480). This results in male tadpoles often with three testes and three ovaries, and with hormone levels so incredibly disturbed that these hermaphrodites produce eggs as tadpoles! The EPA sets the standard for safe levels of atrazine in drinking water at 3 ppb (parts per billion), but levels as low as 0.1 ppb of atrazine in water turned Xenopus tadpoles into hermaphrodites, and doses of 1 ppb had the effect of producing frogs with extremely reduced muscles in the larynx, rendering them unable to call to attract mates.

With this knowledge, Hayes then turned his attention to the real world where he and his colleagues studied leopard frogs, Rana pipiens, from California to Illinois. They found the same types of malformations, ones that the casual observer would not notice, but which cause infertility and hence population decline. The more contaminated the water with atrazine, the worse the sexual deformities.

Could atrazine be the cause of worldwide amphibian decline? Atrazine is used in over eighty countries, most of it on corn, sugar and sorghum. In the U.S. alone, farmers use over sixty million pounds of it annually, and they use it in the spring when tadpoles are developing. Atrazine breaks down fast, but before it does, it gets into streams and rivers and even into the rain water. According to a review in October's Natural History Magazine, levels of atrazine in the water in farming areas may contain as much as 100 to 2,300 ppb. Rainwater in the same areas may have up to 40 ppb. Even in nonagricultural areas, 1 ppb, ten times the dose which produced hermaphrodism in frogs, may be raining down on us.

In the past few years there have been many findings in the wild of malformed frogs with extra digits and limbs. It appeared that the frequency of these malformations was increasing and that these frogs were found in seemingly unpolluted water. The work of Jim Kezer's colleague Stan Sessions proved that the malformations were caused by a trematode infection. Now J.M.Kiesecker from Pennsylvania State University has published a study of wood frogs in Pennsylvania that shows that although trematode infection was always present in frogs with deformities, those frogs living in areas with higher levels of agricultural runoff had a higher incidence of leg deformities (PNAS 99:9900-9904). Laboratory experiments showed that frogs exposed to the EPA's "safe drinking water" standard of 3 ppb of atrazine had increased incidents of trematode infection and subsequent limb deformities. Kiesecker also exposed his laboratory frogs to low levels of the pesticides Malathion and Estenvalerate with the same results. Clearly exposure to agricultural chemicals, even in very low levels, disrupts the immune response in amphibians. It seems that very low levels of our agricultural poisons are probably contributing more than other factors, such as habitat loss or increased levels of UVB in the sunlight, to the long observed worldwide decline in amphibians.

Are we close to experiencing a silent spring, or is it here already? Costa Rica's golden toads have been gone for over a decade. What other species have been lost? Is atrazine responsible for the less publicized reductions in salamander populations in the Pacific Northwest? What can we do? Buy organic products. Write to members of the House and Senate Agriculture Committees. Most importantly, spread the word. Talk to people about what you know about frogs and subtle poisons. Get people energized. Remember DDT and Rachel Carson's Silent Spring? Maybe it's not too late for the frogs either.

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