posed toad embryos in the lab to healthy rainbow trout, infected trout, and trout raised in a hatchery. About 15% of the embryos died of fungal infections when exposed to infected and hatchery-raised fish, suggesting that seemingly healthy hatchery fish may transmit the fungus directly to toad embryos. Toad embryos exposed to experimental soil developed fungal infections only from soil that had been in contact with heavily infected fish. Although only 15% of the toad embryos in the lab developed infections, that number is expected to jump in the field, where low water levels are exposing eggs to stressful UV-B radiation, Kiesecker says. His previous research (Nature 2001, 410, 681–683) has shown that more than 50% of toad embryos die of fungal infections in waters made shallow by climateinduced drops in rain and snowfall. (Conserv. Bio. 2001, 15, 1–8)
Hatchery fish contribute to frog and toad declines
COREL
Global frog, toad, and salamander declines in recent decades have been linked to climate change, increased exposure to UV-B radiation, and pathogens (Environ. Sci. Technol. 1998, 32, 352A). This list of threats now includes hatcheryreared fish, which may be infecting toads in the Cascade Mountains of Oregon with a lethal fungus, according to new research from Joe Kiesecker, a biologist at Pennsylvania State University. Mountain lakes in Oregon are annually stocked with more than 10.5 million rainbow, brook, and brown trout raised in hatcheries, Kiesecker says. Reared in unnaturally crowded conditions, the fish are susceptible to infections by the water fungus Saprolegnia ferax, which is lethal to western toad embryos.
Kiesecker and his colleagues hypothesized that western toad (Bufo boreas) embryos may pick up the fungus directly from infected fish or from lake and stream soil carrying fungus left by sick fish. They ex-
Wind energy’s competitive edge The costs of energy produced by wind-driven turbines are now less than those of energy generated from burning coal in power plants, say Mark Jacobson and Gilbert Masters of California’s Stanford University in a Science Policy Forum article. Although countries such as Germany and Denmark have made extensive commitments to using wind energy—2554 and 2300 MW, respectively—the United States has failed to maximize its wind potential, they say. Under the 1997 Kyoto Protocol, the United States proposed to reduce greenhouse gas emissions by 7% below 1990 levels. This goal can be achieved, the researchers suggest, by replacing 59% (1.11 × 1012 kWh/yr) of existing coal energy with approximately one-quarter million 1500-kW wind energy turbines, spaced at six turbines per square kilometer over farmland or ocean having an area of about 38,000 km2. This is equivalent
BRITT ERICKSON
Research M Watch
to the combined land area covered by the states of Maryland and Connecticut. There are concerns about possible harm to migrating birds by rotating turbine propellers. But this problem can be addressed, say the scientists, by siting turbines out of bird migration paths, thereby minimizing collateral damages. They also note that another problem, the costs of adding transmission lines to provide energy from remotely sited turbines, can be significantly reduced by massproducing the turbines. (Science 2001, 293, 1438)
Tomato plants tolerate high salt Twenty-five percent of irrigated farmland, representing 60 million hectares worldwide, has been damaged by salt and is therefore unsuitable for growing most plants. Rather than removing salt from the land, Hong-Xia Zhang of the University of Toronto (Canada) and Eduardo Blumwald at the University of California–Davis have taken another approach—genetically engineering plants to make them more tolerant of salt. The researchers demonstrate that transgenic tomato plants can thrive in salty conditions by storing salt in the leaves of the plant, while the fruit remains salt-free. Excess sodium ions disrupt vital plant biochemistry and water transport through membranes. Salt tolerance is a complex trait, but some researchers have accomplished the
OCTOBER 1, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
I
402 A
EDUARDO BLUMWALD
demonstrated sodium−proton exchange at rates 7 times higher than wild-type exchanges. Potassium ion exchanges were also affected. On the basis of content analysis, transgenic plants have apparently overcome the nutrient acquisition impairment induced by toxic levels of sodium by forcing more potassium into the fruit and retaining the sodium in the leaves. Transgenic leaves were found to have up to 28 times the sodium of wild-type leaves. Proline levels, a documented osmotic pressure adjustment chemical and scavenger for hydroxyl radicals to protect macromolecules, increased up to fivefold in the transgenic plants. (Nature Biotechnol. 2001, 19, 765–768)
Rainfall + runoff = disease
(Top)Controland (bottom)transgenic tomato plantsgrow ing in the presence of200mM NaCl.
effect by overexpressing a single gene responsible for the coupling of sodium and proton ion transport balance across the vacuolar membrane in Arabidopsis thaliana, a commonly used plant model. Zhang and Blumwald introduced the particular A. thaliana gene that codes for the vacuolar transporter into the genome of a tomato plant (Lycopersicon esculentum). Wild-type and two independent lines of transgenic tomato plants were grown hydroponically. The wild types died or were severely stunted after exposure to 200 mM sodium chloride, yet the transgenic types grew, flowered, and produced fruit. After confirming the transgenic presence, tonoplast (vacuolar membrane) vesicles from the leaves
More than half of the U.S. waterborne disease outbreaks that occurred over the past 50 years were preceded by extreme precipitation, according to researchers at Johns Hopkins University (JHU). Their study is the first to quantify the relationship between heavy rainfall events and waterborne disease outbreaks at the national level over an extended period. Plotting data from the U.S. EPA’s waterborne disease database and the National Climatic Center’s precipitation database in geographic information systems format, JHU’s Jonathan Patz and colleagues report that approximately 24% of the 548 reported outbreaks from 1948 to 1994 resulted from surface water contamination and 36% from groundwater contamination. The researchers determined more than half of the outbreaks to be “acute gastrointestinal illness”, 13% of which were attributed to Giardia. The number of outbreaks was highest during the summer months. Sources of contamination include leaky septic tanks and agricultural runoff. Moreover, in many communities, sewer systems and treatment plants are designed to discharge excess wastewater directly into surface water bodies when treatment capacity is exceeded during periods of heavy rainfall or snowmelt. Under conditions of high soil saturation, the rapid transport of microbial organisms can be enhanced, according to the study. The researchers note that increased turbidity loads caused by heavy rainfall and
runoff compromised the drinking water treatment plant’s efficiency in the 1993 Cryptosporidium outbreak in Milwaukee, WI—the largest waterborne disease outbreak ever documented. With projections of more intense rainfall accompanying global warming, the researchers warn that it is biologically plausible for these increases in rainfall and runoff intensity to result in more contamination of source waters. (Am. J. Public Health 2001, 91, 1–7)
Designer metal-accumulating plants The genes that allow a wild mustard plant to accumulate nickel have been identified by a Purdue University scientist. The discovery could lead to new crop plants that can clean up polluted industrial sites and new foods that provide essential micronutrients. More than 350 species of plants are known to accumulate metals, such as nickel, zinc, copper, cadmium, selenium, and manganese, in high levels. The mustard plant, Thlaspi goesingense, which is only found in the Austrian Alps, has the rare ability to take up large amounts of nickel. It can accumulate 10,000 parts per million (ppm) of nickel compared with 10–100 ppm in an ordinary nonmetal-accumulating plant. Metal-“hyperaccumulating” plants found in nature are small and slowgrowing, which make them impractical for use in cleaning up large metal-contaminated sites. But now that the genes responsible for metal absorption have been found, they could be inserted into fast-growing, large plants, such as grasses. “This is really one of the first tools that we’ve got to manipulate this process of metal hyperaccumulation,” says project leader David Salt. “So what we’re going to do now is to start expressing these genes in nonaccumulating plants to see if we can turn them into metal-accumulating plants.” The hyperaccumulating genes could also be used to produce foods that contain metal micronutrients. Some metals are essential for health in small quantities but are missing from the diet of people living in certain regions. (Proc. Natl. Acad. Sci. U.S.A. 2001, 98, 9995–10,000)
OCTOBER 1, 2001 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
I
403 A
