Environmental ▼ News is for one hind limb to be more affected than the other (unilateral and asymmetric), hinting that perhe first quantitative assessment southern latitudes in South America haps UV is not playing a role in these of the relationship between exwhere the stratospheric ozone layer malformations, Sparling says. posure to solar ultraviolet (UV) is thinner than for most of North Ankley’s colleagues also mearadiation and frog malformations America. sured UV penetration in 26 wetfound that as the intensity of sunAnkley and his colleagues generlands in Minnesota and Wisconsin light increases, so does mortality ated the UV dose–response relationand found that 99% of UV-B never and the number of malformations. ship by exposing northern leopard makes it past the top 5–20 cm of Published in three papers in this frogs (Rana pipiens) at all stages of the water column, thanks to high issue (pp. 2853–2874), the dose– their development to natural light, levels of dissolved organic carbon response studies yield a UV risk ranging in intensity from 25 to 100% (DOC) strongly absorbing UV light. assessment framework that Field measurements of could help scientists untangle DOC and UV-B light were the multiple causes behind used to generate a model that the rise in frog malformations predicts light levels, says Steve over the last decade. Diamond, environmental The research shows that toxicologist at EPA’s research about half of larval frogs die laboratory in Duluth. When when subjected to “full” suncombined with their UV light and that the number of dose–response relationship malformed frogs increases for northern leopard frogs, steadily from none with a the model indicates that UV dose of 25% sunlight to 97% light is not a big threat to with exposure to 100% sunMinnesota frogs, where most light. Although previous wetlands are rich in DOC. studies have associated UV However, UV could still play exposure with limb malformaa role in wetlands with clear tions in amphibians (frogs water and in mountainous and salamanders), the UV habitats low in DOC, says dose was never measured Steve Corn, USGS zoologist EPA toxicologist Greg Peterson and his colleagues under controlled conditions in Missoula, Mont. New refound that Minnesota frogs are protected by UV-absorbor related to effects, says Gary search by Sparling and his ing dissolved organic carbon at the water’s surface. Ankley, toxicologist at EPA’s recolleagues suggests that the search laboratory in Duluth, Minn. of unaltered outdoor sunlight. They UV-type of bilateral and symmetric Elevated levels of UV light due to also exposed the frogs to sunlight filmalformations are found in high, thinning of the stratospheric ozone tered through glass or acrylamide clear lakes in the Rocky Mountains. layer, combined with chemicals and plastic to screen out the UV-B (290– In addition, global warming is foreparasitic infections, are suspected to 320 nm) and UV-B plus UV-A (290– casted to reduce DOC, which could be causes of the worldwide increase 380 nm) portions of the spectrum. increase the threat to amphibians, in amphibian malformations and The experiments demonstrate that says Corn. declining populations. Although no UV-B is largely responsible for the The new studies, together with hard numbers are available, scienmalformations. recent research linking amphibian tists agree it is a real trend, with as Because nearly all the malformamalformations in the western United many as 80% of the frogs in some tions in the study consisted of identiStates with parasitic infections Minnesota wetlands having malforcal missing or shortened hind limb (Ecol. Monogr. 2002, 72, 151–168), mations, says Don Sparling, research bones (bilateral and symmetric), it is represent a real breakthrough, acbiologist with the U.S. Geological tempting to speculate that this patcording to Sparling. What hasn’t Survey (USGS). Moreover, because tern constitutes a fingerprint for been looked at are the complex these measurements were made in UV-caused malformations, Sparling ways that UV and chemical polluMinnesota, researchers suspect that says. But the malformation pattern tants, such as pesticides, could inthe UV risk ought to be higher for of most wild frogs in Minnesota teract to cause malformations, he locations such as montane lakes at (Environ. Sci. Technol. 1997, 31, 552A) adds. —JANET PELLEY
New light on frog malformations
GEORGIA RIEDEL
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ENVIRONMENTAL SCIENCE & TECHNOLOGY / JULY 1, 2002
© 2002 American Chemical Society
