Improving exposure assessment in environmental epidemiology: Application of spatio-temporal visualization tools

A thorough assessment of human exposure to environmental agents should incorporate mobility patterns and temporal changes in human behaviors and concentrations of contaminants; yet the temporal dimension is often under-emphasized in exposure assessment endeavors, due in part to insufficient tools for visualizing and examining temporal datasets. Spatio-temporal visualization tools are valuable for integrating a temporal component, thus allowing for examination of continuous exposure histories in environmental epidemiologic investigations. An application of these tools to a bladder cancer case-control study in Michigan illustrates continuous exposure life-lines and maps that display smooth, continuous changes over time. Preliminary results suggest increased risk of bladder cancer from combined exposure to arsenic in drinking water (>25 g/day) and heavy smoking (>30 cigarettes/day) in the 1970s and 1980s, and a possible cancer cluster around automotive, paint, and organic chemical industries in the early 1970s. These tools have broad application for examining spatially- and temporally-specific relationships between exposures to environmental risk factors and disease.This study was supported by grant R01 CA96002-10, Geographic-Based Research in Cancer Control and Epidemiology, from the National Cancer Institute. Development of the STIS^TM software was funded by grants R43 ES10220 from the National Institutes of Environmental Health Sciences and R01 CA92669 from the National Cancer Institute. Access to cancer case records was provided by Michigan Cancer Surveillance Program within the Division for Vital Records and Health Statistics, Michigan Department of Community Health. The authors thank Michigan Public Health Institute for conducting the telephone interview and Stacey Fedewa and Lisa Bailey for entering written surveys into a database. The authors thank 3 anonymous reviewers for their helpful comments.     

Incipient hydrothermal alteration of basalts and the origin of martian soil

The martian soil is a fine-grained regolith that is chemically basaltic in character with evidence for both gains and losses of volatile and mobile elements compared to martian basalt compositions. These chemical fractionations provide clues to geochemical processes on the surface of Mars. Geochemical processes contributing to the soil proposed in the past include the chemical and mechanical breakdown of rocks under surface conditions, the addition of volcanic aerosols containing S and Cl compounds, and the alteration of basaltic glass to palagonite. Our studies of terrestrial analogs suggest that hydrothermal alteration processes involving impact craters and volcanism could also contribute to the major element trends observed in martian soil. Data from Viking, Pathfinder, and the current MER missions consistently show that relative to basaltic martian meteorite compositions, the major element compositions of the soils are (1) depleted in the fluid-mobile element calcium, (2) generally similar or somewhat enriched in iron oxide and magnesium but MgO depleted compared to Gusev rocks, (3) locally variable in potassium, (4) possibly poorer in aluminum, and (6) very enriched in chlorine and sulfur. The major element trends, aside from the Cl and S enrichment, could be explained by the formation or addition of palagonite according to McSween and Keil (2000), but the missing CaO remains a problem. The chlorine and sulfur are probably derived from other processes such as volcanic aerosols and hydrothermal fluids. McSween and Keil (2000) also argued that hydrothermal alteration of basalts produce alteration trends that are inconsistent with the Mars soil, but this study concludes otherwise. We have used quantitative mass balance mixing models to investigate possible models involving mixtures of basaltic compositions with different types of alteration materials, including palagonite. We show that the Mars soil composition can be matched with a combination of unweathered basaltic martian meteorites with basaltic FeO-rich, CaO-poor alteration products. Palagonite is a possible, but not a necessary component of successful model mixtures. The hydrothermal alteration materials that form successful model mixtures are formed in low temperature, low water/rock ratio environments, and they can reproduce the required geochemical trends because they are poorer in CaO but not in FeO compared to their respective protoliths. These results argue that material altered by hydrothermal processes could be a plausible component of the soil, and that removal of CaO from the soil into some undiscovered reservoir after its formation is not required. The current soil on Mars, therefore, did not have to undergo an episode of in situ aqueous alteration but could represent a sink for materials that experienced aqueous processes in a different setting before erosion to form the soil. The soil can also represent a sink for mobile elements (e.g., S, Cl, and Br) derived from other sources such as volcanic aerosols and hydrothermal fluids.     

International accreditation of sandwich hybridisation assay format DNA probes for micro‐algae

The sandwich hybridisation assay (SHA) is a DNA probe‐based method for rapid identification and enumeration of toxic micro‐algae which uses species specific oligonucleotide probes targeted at ribosomal RNA. It is suited to fragile micro‐algal cells which commonly collapse during the fixation stage of sample collection, compromising identification by traditional microscopy. The assay has been available for research for several years, but was validated and accepted for international accreditation for commercial laboratory use in New Zealand in May 2004 (International Accreditation New Zealand: ISO 17025). During the validation of the raphidophyte assay, some discrepancies were noted between SHA cell concentration estimates and traditional light microscope cell counts. Higher SHA estimates were recorded when blooms had collapsed but rRNA was still present in sea water. Conversely, higher traditional cell counts occurred when sample delivery was delayed more than 48 h, presumably owing to degradation of rRNA in the live cultures used for the SHA. SHA cell concentration estimates of the toxic diatom bloom‐former Pseudo‐nitzschia australis were also compared with whole cell format DNA probe counts and traditional microscope counts; SHA counts were comparable for the three methods tested.     

Decadal temperature changes in the Tasman Sea

Ocean temperature changes between 1991 and 2005 in the eastern Tasman Sea were analysed. This area was chosen because of a combination of data availability, low mesoscale variability and because of its importance in determining the climate of the downwind New Zealand landmass. A large warming extending to the full depth of the water column (c. 800 m) was found to have occurred between 1996 and 2002. This warming was seen in measurements by expendable bathythermographs and also in satellite sea surface temperature and sea surface height products, and has a clear impact on New Zealand's terrestrial temperature. The nature of the warming is discussed, together with likely forcing mechanisms. No local forcing mechanisms are consistent with the observed warming, leading to the conclusion that the signal seen in the Tasman Sea is part of a larger South Pacific‐wide phenomenon.     

Radar imagery of Mercury’s putative polar ice: 1999-2005 Arecibo results

We present an updated survey of Mercury’s putative polar ice deposits, based on high-resolution (1.5-km) imaging with the upgraded Arecibo S-band radar during 1999-2005. The north pole has now been imaged over a full range of longitude aspects, making it possible to distinguish ice-free areas from radar-shadowed areas and thus better map the distribution of radar-bright ice. The new imagery of the south pole, though derived from only a single pair of dates in 2005, improves on the pre-upgrade Arecibo imagery and reveals many additional ice features. Some medium-size craters located within 3° of the north pole show near-complete ice coverage over their floors, central peaks, and southern interior rim walls and little or no ice on their northern rim walls, while one large (90 km) crater at 85°N shows a sharp ice-cutoff line running across its central floor. All of this is consistent with the estimated polar extent of permanent shading from direct sunlight. Some craters show ice in regions that, though permanently shaded, should be too warm to maintain unprotected surface ice owing to indirect heating by reflected and reradiated sunlight. However, the ice distribution in these craters is in good agreement with models invoking insulation by a thin dust mantle. Comparisons with Goldstone X-band radar imagery indicate a wavelength dependence that could be consistent with such a dust mantle. More than a dozen small ice features have been found at latitudes between 67° and 75°. All of this low-latitude ice is probably sheltered in or under steep pole-facing crater rim walls, although, since most is located in the Mariner-unimaged hemisphere, confirmation must await imaging by the MESSENGER orbiter. These low-latitude features are concentrated toward the “cold longitudes,” possibly indicating a thermal segregation effect governed by indirect heating. The radar imagery places the corrected locations of the north and south poles at 7°W, 88.35°N and 90°W, 88.7°S, respectively, on the original Mariner-based maps.     

Comparison of Lower-Tropospheric Temperature Climatologies and Trends at Low and High Elevation Radiosonde Sites

Observations of rapid retreat of tropical mountain glaciers over the past two decades seem superficially at odds with observations of little or no warming of the tropical lower troposphere during this period. To better understand the nature of temperature and atmospheric freezing level variability in mountain regions, on seasonal to multidecadal time scales, this paper examines long-term surface and upper-air temperature observations from a global network of 26 pairs of radiosonde stations. Temperature data from high and low elevation stations are compared at four levels: the surface, the elevation of the mountain station surface, 1 km above the mountain station, and 2 km above the mountain station. Climatological temperature differences between mountain and low elevation sites show diurnal and seasonal structure, as well as latitudinal and elevational differences. Atmospheric freezing-level heights tend to decrease with increasing latitude, although maximum heights are found well north of the equator, over the Tibetan Plateau. Correlations of interannual anomalies of temperature between paired high and low elevation sites are relatively high at 1 or 2 km above the mountain station. But at the elevation of the station, or at the two surface elevations, correlations are lower, indicating decoupling of the boundary layer air from the free troposphere.Trends in temperature and freezing-level height are generally upward, both during 1979–2000 and during longer periods extending back to the late 1950s. However, some negative trends were found at extratropical locations. In many cases, statistically significant differences were found in trends at paired high and low elevation stations, with tropical pairs revealing more warming (and greater increases in freezing-level height) at mountain stations than at low elevations. This result is consistent with both the observed retreat of tropical glaciers and the minimal change in tropics-wide tropospheric temperatures over the past two decades.Overall, the analysis suggests that, on diurnal, seasonal, interannual, and multidecadal time scales, temperature variations at mountain locations differ significantly from those at relatively nearby (a few hundred kilometers) low elevation stations. These differences are greatest at the two surface levels, but can persist up to 2 km above the mountain site. Therefore, to determine the nature of climate variability at high elevation sites requires local observations, since large-scale patterns derived from low elevation observations may not be representative of the mountain regions. Conversely, temperature change in mountain regions should not be viewed as necessarily representative of global surface or tropospheric trends.     

Diagenetic controls on the isotopic composition of carbonate‐associated sulphate in the Permian Capitan Reef Complex,West Texas

Late Palaeozoic‐age strata from the Capitan Reef in west Texas show facies‐dependent heterogeneity in the sulphur isotopic composition of carbonate‐associated sulphate, which is trace sulphate incorporated into carbonate minerals that is often used to reconstruct the sulphur isotopic composition of ancient seawater. However, diagenetic pore fluid processes may influence the sulphur isotopic composition of carbonate‐associated sulphate. These processes variously modify the sulphur isotopic composition of incorporated sulphate from syndepositional seawater in shelf crest, outer shelf, shelf margin and slope depositional settings. This study used a new multicollector inductively‐coupled plasma mass spectrometry technique to determine the sulphur isotopic composition of samples of individual depositional and diagenetic textures. Carbonate rocks representing peritidal facies in the Yates and Tansill formations preserve the sulphur isotopic composition of Guadalupian seawater sulphate despite alteration of the carbon and oxygen isotopic compositions by meteoric and dolomitizing diagenetic processes. However, sulphur isotopic data indicate that limestones deposited in reef and slope facies in the Capitan and Bell Canyon formations largely incorporate sulphate from anoxic marine‐phreatic pore fluids isotopically modified from seawater by microbial sulphate reduction, despite generally preserving the carbon and oxygen isotopic compositions of Permian seawater. Some early and all late meteoric calcite cements have carbonate‐associated sulphate with a sulphur isotopic composition distinct from that of Permian seawater. Detailed petrographic and sedimentary context for carbonate‐associated sulphate analyses will allow for improved reconstructions of ancient seawater composition and diagenetic conditions in ancient carbonate platforms. The results of this study indicate that carbonate rocks that diagenetically stabilize in high‐energy environments without pore fluid sulphate gradients can provide a robust archive of ancient seawater's sulphur isotopic composition.