Uptake rates of thorium progeny in a semiarid environment

The release rates and transformation processes that influence the mobility, biological uptake, and transfer of radionuclides are essential to the assessment of the health effects in the food chain and ecosystem. This study examined concentrations of 222Th in both soil and vegetation at a closed military training site, Kirtland Air Force Base (KAFB), New Mexico. Brazilian sludge was intentionally introduced into the topsoil in the early 1960s to simulate nuclear weapon accidents. Soil (60) and vegetation (120) samples were collected from 1996 to 2000 and analyzed for radionuclides and progeny. High-resolution gamma-ray spectroscopy was used to determine radionuclide activities. The results indicate that the thorium progeny were the predominant contaminant in soil and vegetation. Concentration ratios (CRs) were calculated based on actinium levels.     

Discrimination of flicker frequency rates in the reptile tuatara (Sphenodon )

By investigating the mechanisms that underlie the perception of environmental cues, we may begin to understand how the sensory system governs behavioral responses. This is the first empirical study to examine learning and visual sensitivity in a reptile species, the tuatara (Sphenodon punctatus). We established a non-intrusive psychophysical method by employing an instrumental paradigm in order to examine discrimination learning and the ability to distinguish different flicker frequencies in the tuatara. Seventeen tuatara were trained under an operant conditioning task to respond to various discriminative stimuli flickering between 2.65 and 65.09 Hz. Tuatara were able to learn the operant task and discriminate between a constant light and flicker frequency rates between 2.65 and 45.61 Hz, but not at 65.09 Hz. We demonstrated a reliable psychophysical method where these reptiles could learn a basic operant task and discriminate visual stimuli in the form of flicker frequency rates. The tuatara’s ability to perceive flickering light is comparable to that of avian, mammalian, and other reptilian species. This method is thus suitable for more comprehensive examinations of vision and additional sensory abilities in other reptiles. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Emergence cues of a mayfly in a high-altitude stream ecosystem: potential response to climate change.

To understand the consequences of human accelerated environmental change, it is important to document the effects on natural populations of an increasing frequency of extreme climatic events. In stream ecosystems, recent climate change has resulted in extreme variation in both thermal and hydrological regimes. From 2001 to 2004, a severe drought in western United States corresponded with earlier emergence of the adult stage of the high-altitude stream mayfly, Baetis bicaudatus. Using a long-term database from a western Colorado stream, the peak emergence date of this mayfly population was predicted by both the magnitude and date of peak stream flow, and by the mean daily water temperature, suggesting that Baetis may respond to declining stream flow or increasing water temperature as proximate cues for early metamorphosis. However, in a one-year survey of multiple streams from the same drainage basin, only water temperature predicted spatial variation in the onset of emergence of this mayfly. To decouple the effects of temperature and flow, we separately manipulated these factors in flow-through microcosms and measured the timing of B. bicaudatus metamorphosis to the adult stage. Mayflies emerged sooner in a warmed-water treatment than an ambient-water treatment; but reducing flow did not accelerate the onset of mayfly emergence. Nonetheless, using warming temperatures to cue metamorphosis enables mayflies to time their emergence during the descending limb of the hydrograph when oviposition sites (protruding rocks) are becoming available. We speculate that large-scale climate changes involving warming and stream drying could cause significant shifts in the timing of mayfly metamorphosis, thereby having negative effects on populations that play an important role in stream ecosystems.     

Patterns of organochlorine pesticide contamination in neotropical migrant passerines in relation to diet and winter habitat

Eleven species of Neotropical migrant passerines collected in Illinois (USA) during May 1996, were analyzed for the presence of organochlorine (OC) pesticides. At least one of five OC pesticide residues was detected in 66 of 72 birds, representing all species examined. The contaminants most frequently detected were p,p'-DDE, dieldrin and heptachlor epoxide, all of which were present in the 10-30 ng/g range. Insectivores had significantly higher levels of these compounds than did non-insectivores, while there was no significant main effect of winter habitat (forest and scrub). Future research on OC pesticide contamination in resident New World passerines may allow more accurate predictions regarding the sources of contamination in Neotropical migrants.     

Assessing workplace chemical exposures: the role of exposure monitoring

Occupational exposure is the condition of being subjected through employment to a chemical, physical, or biological agent, or to a specific process, practice, behavior, or organization of work. Exposure to a chemical agent is typically the contact of that agent with the outer boundary of a subject, such as the respiratory system, skin, or digestive system. In occupational hygiene we are most concerned with exposure through the respiratory system, although, increasingly we are concerned with the results of dermal exposures, including those exposures to the skin that can be transferred to the mouth and digestive system. This presentation will detail methods available for assessing personal exposures to chemicals through monitoring. The results from monitoring can then be compared to established guidelines and regulations, although this is not the only rationale for making measurements. These monitoring methods are currently used around the world to establish the benchmark hazard from which risk to the worker can be predicted. The presentation will describe the general techniques for assessing exposures to the respiratory system from chemical gases and vapors, chemical dusts, and exposures to the skin from bulk chemicals or chemical contamination of surfaces. For respiratory exposures, direct-reading instruments are available for spot measurements, and for monitoring short-term fluctuations in concentration. However, most standards and regulations are based on time-integrated (time-weighted average) exposures, requiring longer-term integrative methods. Therefore, the specific focus of this review will be the methods available for full work-shift sampling. For gases and vapors this will include taking whole-air samples in canisters or polymer bags, or concentration of chemicals by absorption in liquids or adsorption on solid sorbents, with subsequent chemical analysis. Chemical concentration can take place by pumping air through the sorbing media, or by allowing molecules to diffuse to the sorbent surface. Transfer of the collected chemicals to the analytical instrumentation can be accomplished using solvent displacement and injection, or through the application of heat to bring the collected molecules back into the vapor phase. For particles, the particle size is important as this determines the site of deposition in the lungs, and so time-integrated sampling on filters using various types of size-selective samplers is preferred. Finally, some techniques that have been used to assess the potential for chemical contamination of the skin are presented. Biomonitoring is another tool that can be used to assess exposure, and the results are more relevant to dosimetric considerations than exposure. Biomonitoring is a complex subject worthy of a separate review, and will be considered only briefly here.     

Common ectomycorrhizal networks may maintain monodominance in a tropical rain forest

Most tropical rain forests contain diverse arrays of tree species that form arbuscular mycorrhizae. In contrast, the less common monodominant rain forests, in which one tree species comprises more than 50% of the canopy, frequently contain ectomycorrhizal (ECM) associates. In this study, I explored the potential for common ECM networks, created by aggregations of ECM trees, to enhance seedling survivorship near parent trees. I determined the benefit conferred by the common ECM network on seedling growth and survivorship of an ECM monodominant species in Guyana. Seedlings with access to an ECM network had greater growth (73% greater), leaf number (55% more), and survivorship (47% greater) than seedlings without such access, suggesting that the ECM network provides a survivorship advantage. A survey of wild seedlings showed positive distance-dependent distribution and survival with respect to conspecific adults. These experimental and survey results suggest that the negative distance-dependent mechanisms at the seedling stage thought to maintain tropical rain forest diversity are reversed for ECM seedlings, which experience positive feedbacks from the ECM network. These results may in part explain the local monodominance of an ECM tree species within the matrix of high-diversity, tropical rain forest.     

Sulfuric acid at workplaces--applicability of the new Indicative Occupational Exposure Limit Value (IOELV) to thoracic particles

Until 2009, the limit values for airborne sulfuric acid in Europe were based on the inhalable particle fraction (e.g. MAK (Maximum allowed concentration at workplace) value 0.1 mg m(-3) as the inhalable fraction). With the publication of the Commission Directive 2009/161/EU, an Indicative Occupational Exposure Limit Value (IOELV) of 0.05 mg m(-3) for sulfuric acid aerosols was based for the first time on the thoracic particle fraction. To permit a comparison of the measured values for the inhalable fraction with those of the thoracic fraction and to quantify the thoracic fraction, a cyclone was fabricated out of sulfuric-acid-resistant stainless steel that achieves suitable collection characteristics (PM(10)) at a flow rate of 5.34 L min(-1). 49 measurements were carried out in parallel in 21 companies. At concentrations well below the IOELV, there is little difference between the thoracic and inhalable particle concentrations. At higher concentrations (>0.1 mg m(-3) inhalable aerosol), larger droplets have a marked effect on the measured values and the thoracic fraction accounts for only 32.1 ± 12.5% of the inhalable fraction. The EU's IOELV and the proposal of the MAK Commission therefore provide a comparable level of protection. In the transposition of the IOELV into national law, an air limit of 0.1 mg m(-3) could therefore be implemented for the inhalable fraction.     

A Hydrologic Drying Bias in Water‐Resource Impact Analyses of Anthropogenic Climate Change

For water‐resource planning, sensitivity of freshwater availability to anthropogenic climate change (ACC) often is analyzed with “offline” hydrologic models that use precipitation and potential evapotranspiration (E_p) as inputs. Because E_p is not a climate‐model output, an intermediary model of E_p must be introduced to connect the climate model to the hydrologic model. Several E_p methods are used. The suitability of each can be assessed by noting a credible E_p method for offline analyses should be able to reproduce climate models’ ACC‐driven changes in actual evapotranspiration in regions and seasons of negligible water stress (E_w). We quantified this ability for seven commonly used E_p methods and for a simple proportionality with available energy (“energy‐only” method). With the exception of the energy‐only method, all methods tend to overestimate substantially the increase in E_p associated with ACC. In an offline hydrologic model, the E_p‐change biases produce excessive increases in actual evapotranspiration (E), whether the system experiences water stress or not, and thence strong negative biases in runoff change, as compared to hydrologic fluxes in the driving climate models. The runoff biases are comparable in magnitude to the ACC‐induced runoff changes themselves. These results suggest future hydrologic drying (wetting) trends likely are being systematically and substantially overestimated (underestimated) in many water‐resource impact analyses.