Research▼Watch Fate of agricultural NH3 emissions Researchers in North Carolina have found a direct correlation between ammonia (NH3) emissions from agricultural practices and atmospheric ammonium (NH4+) concentrations associated with aerosols and precipitation. The results provide information about the fate of gaseous NH3 emissions and could help in developing models to predict the transport and deposition of atmospheric NHx (NH4+ + NH3). The fate of NH3 emissions in the United States, 90% of which come from agricultural sources, is difficult to analyze because of a lack of monitoring data on gaseous NH3 in ambient air and the complex relationships between NH3, sulfate and nitrate particles, and HNO3 gas. Acid deposition monitoring networks, however, provide large amounts of data on NH4+ concentrations in fine particulate matter. Because high concentrations of NHx at the Earth’s surface can lead to acidification of soils, loss of forests, and eutrophication of waterways, it is important to know the spatial distribution and fate of NH3 emissions. Viney Aneja of North Carolina State University and colleagues examined the seasonal and spatial trends in atmospheric NH4+ concentrations and NH3 emissions in the southeastern United States over the period 1990–1998. They found that NH4+ concentrations associated with aerosols increased with higher NH3 emissions; however, NH4+ concentrations in precipitation were only weakly correlated with NH3 emissions. The researchers saw higher atmospheric NH4+ concentrations in the summer, presumably because the warmer temperatures led to more NH3 volatilizing from soils and animal waste in lagoons. Because seasonal variations in NH3 emissions could affect ammonium nitrate and sulfate aerosol con-
centrations, the researchers believe further work is needed to investigate the dynamic NH3−aerosol relationships and the influence of NH3 on fine particulate matter. ( J. Geophys. Res. 2003, 108, DOI 10.1029/ 2002JD002271)
Endocrine disrupters defy routine extrapolations To effectively screen chemicals for hormone-disrupting effects, scientists need to begin testing them at the levels at which they are found in the environment, according to a group of scientists from the University of Missouri–Columbia. Wade Welshons and his colleagues used MCF-7 human breast cancer cells to demonstrate how varying the dose of hormone-disrupting chemicals can cause very different responses. For example, they found that 17ß-estradiol stimulated growth in the MCF-7 cells at the low parts-pertrillion level (1.0–100 pM). However, at the high parts-per-trillion and parts-per-billion levels (100 pM to
1 µM), 17ß-estradiol did not induce growth, which the researchers attribute to saturated receptors on the cell walls. At levels of parts per million (1−100 µM), 17ß-estradiol caused acute cytotoxicity that reduced cell growth. This type of nonlinear response pattern renders invalid traditional toxicology methods that rely on linear extrapolation from high-dose results to predict what happens at low doses. (For another perspective, see Environ. Sci. Technol. 2003, 37, 146–151.) The researchers also found that the growth-stimulating effects of estradiol in the low-dose range could be obliterated by the presence of another estrogen such as diethylstilbestrol (DES). Exposing the MCF-7 cells to 3 parts per trillion of DES completely obscured the low-dose effects of estradiol, but it did not impair detection at the high-dose range. For this reason, they argue that studies should include positive and negative controls when evaluating estrogenic activity to ensure that the test system is not contaminated.
MCF-7 dose-response to estradiol The MCF-7 breast cancer cells in this experiment responded very differently to varying levels of the hormone estradiol.
350 300 Breast cancer cell DNA per well, percentage of control
250
Low-dose range
200
High-dose range
150 Control
100 50 0
1 10 100 fg/mL (ppq)
1 10 100 pg/mL (ppt)
1 10 100 ng/mL (ppb)
1 10 100 µg/mL (ppm)
Estradiol concentration (mass per milliliter) Source: Environ. Health Perspect.
MAY 1, 2003 / ENVIRONMENTAL SCIENCE & TECHNOLOGY ■ 173 A
Does ocean methane pose a risk? Methane trapped as hydrates in ocean floor sediments represents an important reservoir of carbon, an untapped energy source, and a potential “time bomb”. There is growing evidence that this methane has been and could again be released during times of rapid climate warming. Now, using a new biomarker to examine historical records, researchers from the University of Bremen in Germany suggest that continuous and widespread methane release could have a profound and lasting effect on aquatic ecosystems and the carbon cycle. Kai-Uwe Hinrichs and co-workers have identified diplopterol, a compound synthesized by aerobic bacteria, including methanotrophic ones, as a biomarker for methane release in water. Diplopterol that is specifically made from methane has lower 13C isotope levels, say the researchers. This gauge of methane activity complements another, albeit controversial, approach that is based on 13C levels in certain fossil records in ocean sediments.
OH
Diplopterol
The researchers searched for the biomarker in sediments from the Santa Barbara Basin and found evidence that ocean levels of methane, which they believe were released from the hydrates, have indeed varied over the past 60,000 years. Similar signals were seen in the fossil record. Significantly, ocean methane levels currently are too low to generate the biomarker signal. Because methanotrophic bacteria consume oxygen, if the methane releases during any of the past events
had been widespread, it might have led to broad suboxic conditions. How much of this methane, which is itself a powerful greenhouse gas, escaped into the atmosphere is not known. (Science 2003, 299, 1214–1217)
Pfiesteria and causes fishkills simultaneously, also fits the data and therefore is worthy of further consideration. (Ecosystems 2003, 6, 11–19)
Humans influence sea-level pressure
Fishkills stimulate Pfiesteria toxicity According to a novel statistical assessment of field data conducted by Duke University researchers, the dinoflagellate Pfiesteria piscicida does not cause NATIONAL OCEANIC AND ATMOSPHERIC ADMIN.
The researchers focused on the mechanisms of action of endocrinedisrupting chemicals with estrogenic activity because they are the most widely studied hormonally active chemicals, but they say the results are applicable for all endocrine disrupters. (Environ. Health Perspect. 2003, DOI 10.1289/ehp.5494)
Pfiesteria piscicida, a dinoflagellate that produces toxins associated with fishkills, has multiple life stages. It is shown here in its zoospore stage.
fishkills; rather, fishkills stimulate Pfiesteria to become toxic. This interpretation may have important implications for water quality management strategies for reducing fishkills and restoring the health of river ecosystems. Craig Stow and Mark Borsuk at Duke University used methods that encompass mathematical advances— namely, introducing a third element into direct cause-and-effect relationships—to analyze data published by Joann Burkholder and other researchers for the Neuse River Estuary in North Carolina. Stow and Borsuk determined that it is statistically implausible for toxic Pfiesteria to cause fishkills. They believe that Pfiesteria are present at some level in the estuary at all times and fishkills promote the growth of the toxic form, which would explain why toxic Pfiesteria are absent under nonfishkill conditions. The researchers caution that Pfiesteria toxin can kill fish in controlled environments, but this does not mean it will do so in nature. They also point out that a model in which fishkills promote toxic Pfiesteria is not the only model consistent with current data. Another model, in which an unidentified variable triggers toxic
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Anthropogenic greenhouse gases and sulfate aerosols have influenced sealevel pressure, according to new research that combines simulations from four climate models. The results provide the first evidence of human influence on climate that is independent of temperature change measurements and suggest that current climate models underestimate the impacts of climate change, particularly on European climate. Nathan Gillett of the University of Victoria in Canada and colleagues at the Meteorological Service of Canada and the Hadley Centre for Climate Prediction and Research in the United Kingdom used sea-level pressure data collected during winter over the period 1948–1998 from three data sets. Decreases in sea-level pressure were observed over the Arctic, Antarctic, and North Pacific Ocean, whereas increases were observed over the subtropical North Atlantic Ocean, southern Europe, and North Africa. The researchers used an approach to compare model simulations and sea-level pressure observations that involved more spatio-temporal information than previous methods. Until now, most comparisons have used indices such as the North Atlantic Oscillation to determine whether observed changes are due to natural variability or anthropogenic sources. Using the new approach, the observed pattern of sea-level pressure trends was similar to that predicted by the four models; however, the results suggest that current climate models substantially underpredict this sea-level pressure response. For example, the effects of the trend in the North Atlantic Oscillation index, which is associated with Eurasian winter warming, increased rainfall in Scotland, decreased rainfall in Spain, and extreme cold events in France, are likely to be underestimated. The authors believe that more realistic predictions of climate change impacts will only be possible if this discrepancy between observations and models is reconciled. (Nature 2003, 422, 292−294)
